Mac OS X Manual Page For postconf(5)

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POSTCONF(5) POSTCONF(5)

NAME
postconf - Postfix configuration parameters

SYNOPSIS
postconf parameter ...

postconf -e "parameter=value" ...

DESCRIPTION
The Postfix main.cf configuration file specifies a small subset of all the parameters that control
the operation of the Postfix mail system. Parameters not specified in main.cf are left at their
default values.

The general format of the main.cf file is as follows:

Each logical line has the form "parameter = value". Whitespace around the "=" is ignored, as
is whitespace at the end of a logical line.

Empty lines and whitespace-only lines are ignored, as are lines whose first non-whitespace
character is a `#'.

A logical line starts with non-whitespace text. A line that starts with whitespace continues a
logical line.

A parameter value may refer to other parameters.

The expressions "$name", "${name}" or "$(name)" are recursively replaced by the value
of the named parameter.

The expression "${name?value}" expands to "value" when "$name" is non-empty. This form
is supported with Postfix version 2.2 and later.

The expression "${name:value}" expands to "value" when "$name" is empty. This form is
supported with Postfix version 2.2 and later.

When the same parameter is defined multiple times, only the last instance is remembered.

Otherwise, the order of main.cf parameter definitions does not matter.

The remainder of this document is a description of all Postfix configuration parameters. Default val-ues values
ues are shown after the parameter name in parentheses, and can be looked up with the "postconf -d"
command.

Note: this is not an invitation to make changes to Postfix configuration parameters. Unnecessary
changes can impair the operation of the mail system.

2bounce_notice_recipient (default: postmaster)
The recipient of undeliverable mail that cannot be returned to the sender. This feature is enabled
with the notify_classes parameter.

access_map_reject_code (default: 554)
The numerical Postfix SMTP server response code when a client is rejected by an access(5) map
restriction.

Do not change this unless you have a complete understanding of RFC 821.

address_verify_default_transport (default: $default_transport)
Overrides the default_transport parameter setting for address verification probes.

This feature is available in Postfix 2.1 and later.

address_verify_local_transport (default: $local_transport)
Overrides the local_transport parameter setting for address verification probes.

This feature is available in Postfix 2.1 and later.

address_verify_map (default: empty)
Optional lookup table for persistent address verification status storage. The table is maintained by
the verify(8) service, and is opened before the process releases privileges.

By default, the information is kept in volatile memory, and is lost after "postfix reload" or "post-fix "postfix
fix stop".

Specify a location in a file system that will not fill up. If the database becomes corrupted, the
world comes to an end. To recover delete the file and do "postfix reload".

Examples:

address_verify_map = hash:/etc/postfix/verify
address_verify_map = btree:/etc/postfix/verify

This feature is available in Postfix 2.1 and later.

address_verify_negative_cache (default: yes)
Enable caching of failed address verification probe results. When this feature is enabled, the cache
may pollute quickly with garbage. When this feature is disabled, Postfix will generate an address
probe for every lookup.

This feature is available in Postfix 2.1 and later.

address_verify_negative_expire_time (default: 3d)
The time after which a failed probe expires from the address verification cache.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

This feature is available in Postfix 2.1 and later.

address_verify_negative_refresh_time (default: 3h)
The time after which a failed address verification probe needs to be refreshed.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

This feature is available in Postfix 2.1 and later.

address_verify_poll_count (default: 3)
How many times to query the verify(8) service for the completion of an address verification request
in progress.

The default poll count is 3.

Specify 1 to implement a crude form of greylisting, that is, always defer the first delivery request
for a never seen before address.

Example:

address_verify_poll_count = 1

This feature is available in Postfix 2.1 and later.

address_verify_poll_delay (default: 3s)
The delay between queries for the completion of an address verification request in progress.

The default polling delay is 3 seconds.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

This feature is available in Postfix 2.1 and later.

address_verify_positive_expire_time (default: 31d)
The time after which a successful probe expires from the address verification cache.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

This feature is available in Postfix 2.1 and later.

address_verify_positive_refresh_time (default: 7d)
The time after which a successful address verification probe needs to be refreshed. The address ver-ification verification
ification status is not updated when the probe fails (optimistic caching).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

This feature is available in Postfix 2.1 and later.

address_verify_relay_transport (default: $relay_transport)
Overrides the relay_transport parameter setting for address verification probes.

This feature is available in Postfix 2.1 and later.

address_verify_relayhost (default: $relayhost)
Overrides the relayhost parameter setting for address verification probes. This information can be
overruled with the transport(5) table.

This feature is available in Postfix 2.1 and later.

address_verify_sender (default: postmaster)
The sender address to use in address verification probes. To avoid problems with address probes that
are sent in response to address probes, the Postfix SMTP server excludes the probe sender address
from all SMTPD access blocks.

Specify an empty value (address_verify_sender =) or <> if you want to use the null sender address.
Beware, some sites reject mail from <>, even though RFCs require that such addresses be accepted.

Examples:

address_verify_sender = <>
address_verify_sender = postmaster@my.domain

This feature is available in Postfix 2.1 and later.

address_verify_sender_dependent_relayhost_maps (default: empty)
Overrides the sender_dependent_relayhost_maps parameter setting for address verification probes.

This feature is available in Postfix 2.3 and later.

address_verify_service_name (default: verify)
The name of the verify(8) address verification service. This service maintains the status of sender
and/or recipient address verification probes, and generates probes on request by other Postfix pro-cesses. processes.
cesses.

address_verify_transport_maps (default: $transport_maps)
Overrides the transport_maps parameter setting for address verification probes.

This feature is available in Postfix 2.1 and later.

address_verify_virtual_transport (default: $virtual_transport)
Overrides the virtual_transport parameter setting for address verification probes.

This feature is available in Postfix 2.1 and later.

alias_database (default: see postconf -d output)
The alias databases for local(8) delivery that are updated with "newaliases" or with "sendmail -bi".

This is a separate configuration parameter because not all the tables specified with $alias_maps have
to be local files.

Examples:

alias_database = hash:/etc/aliases
alias_database = hash:/etc/mail/aliases

alias_maps (default: see postconf -d output)
The alias databases that are used for local(8) delivery. See aliases(5) for syntax details.

The default list is system dependent. On systems with NIS, the default is to search the local alias
database, then the NIS alias database.

If you change the alias database, run "postalias /etc/aliases" (or wherever your system stores the
mail alias file), or simply run "newaliases" to build the necessary DBM or DB file.

The local(8) delivery agent disallows regular expression substitution of $1 etc. in alias_maps,
because that would open a security hole.

The local(8) delivery agent will silently ignore requests to use the proxymap(8) server within
alias_maps. Instead it will open the table directly. Before Postfix version 2.2, the local(8) deliv-ery delivery
ery agent will terminate with a fatal error.

Examples:

alias_maps = hash:/etc/aliases, nis:mail.aliases
alias_maps = hash:/etc/aliases

allow_mail_to_commands (default: alias, forward)
Restrict local(8) mail delivery to external commands. The default is to disallow delivery to "|com-mand" "|command"
mand" in :include: files (see aliases(5) for the text that defines this terminology).

Specify zero or more of: alias, forward or include, in order to allow commands in aliases(5), .for-ward .forward
ward files or in :include: files, respectively.

Example:

allow_mail_to_commands = alias,forward,include

allow_mail_to_files (default: alias, forward)
Restrict local(8) mail delivery to external files. The default is to disallow "/file/name" destina-tions destinations
tions in :include: files (see aliases(5) for the text that defines this terminology).

Specify zero or more of: alias, forward or include, in order to allow "/file/name" destinations in
aliases(5), .forward files and in :include: files, respectively.

Example:

allow_mail_to_files = alias,forward,include

allow_min_user (default: no)
Allow a recipient address to have `-' as the first character. By default, this is not allowed, to
avoid accidents with software that passes email addresses via the command line. Such software would
not be able to distinguish a malicious address from a bona fide command-line option. Although this
can be prevented by inserting a "--" option terminator into the command line, this is difficult to
enforce consistently and globally.

allow_percent_hack (default: yes)
Enable the rewriting of the form "user%domain" to "user@domain". This is enabled by default.

Note: with Postfix version 2.2, message header address rewriting happens only when one of the follow-ing following
ing conditions is true:

The message is received with the Postfix sendmail(1) command,

The message is received from a network client that matches $local_header_rewrite_clients,

The message is received from the network, and the remote_header_rewrite_domain parameter spec-ifies specifies
ifies a non-empty value.

To get the behavior before Postfix version 2.2, specify "local_header_rewrite_clients = static:all".

Example:

allow_percent_hack = no

allow_untrusted_routing (default: no)
Forward mail with sender-specified routing (user[@%!]remote[@%!]site) from untrusted clients to des-tinations destinations
tinations matching $relay_domains.

By default, this feature is turned off. This closes a nasty open relay loophole where a backup MX
host can be tricked into forwarding junk mail to a primary MX host which then spams it out to the
world.

This parameter also controls if non-local addresses with sender-specified routing can match Postfix
access tables. By default, such addresses cannot match Postfix access tables, because the address is
ambiguous.

alternate_config_directories (default: empty)
A list of non-default Postfix configuration directories that may be specified with "-c config_direc-tory" config_directory"
tory" on the command line, or via the MAIL_CONFIG environment parameter.

This list must be specified in the default Postfix configuration directory, and is used by set-gid
Postfix commands such as postqueue(1) and postdrop(1).

always_bcc (default: empty)
Optional address that receives a "blind carbon copy" of each message that is received by the Postfix
mail system.

Note: if mail to the BCC address bounces it will be returned to the sender.

Note: automatic BCC recipients are produced only for new mail. To avoid mailer loops, automatic BCC
recipients are not generated for mail that Postfix forwards internally, nor for mail that Postfix
generates itself.

anvil_rate_time_unit (default: 60s)
The time unit over which client connection rates and other rates are calculated.

This feature is implemented by the anvil(8) service which is available in Postfix version 2.2 and
later.

The default interval is relatively short. Because of the high frequency of updates, the anvil(8)
server uses volatile memory only. Thus, information is lost whenever the process terminates.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

anvil_status_update_time (default: 600s)
How frequently the anvil(8) connection and rate limiting server logs peak usage information.

This feature is available in Postfix 2.2 and later.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

append_at_myorigin (default: yes)
With locally submitted mail, append the string "@$myorigin" to mail addresses without domain informa-tion. information.
tion. With remotely submitted mail, append the string "@$remote_header_rewrite_domain" instead.

Note 1: this feature is enabled by default and must not be turned off. Postfix does not support
domain-less addresses.

Note 2: with Postfix version 2.2, message header address rewriting happens only when one of the fol-lowing following
lowing conditions is true:

The message is received with the Postfix sendmail(1) command,

The message is received from a network client that matches $local_header_rewrite_clients,

The message is received from the network, and the remote_header_rewrite_domain parameter spec-ifies specifies
ifies a non-empty value.

To get the behavior before Postfix version 2.2, specify "local_header_rewrite_clients = static:all".

append_dot_mydomain (default: yes)
With locally submitted mail, append the string ".$mydomain" to addresses that have no ".domain"
information. With remotely submitted mail, append the string ".$remote_header_rewrite_domain"
instead.

Note 1: this feature is enabled by default. If disabled, users will not be able to send mail to
"user@partialdomainname" but will have to specify full domain names instead.

Note 2: with Postfix version 2.2, message header address rewriting happens only when one of the fol-lowing following
lowing conditions is true:

The message is received with the Postfix sendmail(1) command,

The message is received from a network client that matches $local_header_rewrite_clients,

The message is received from the network, and the remote_header_rewrite_domain parameter spec-ifies specifies
ifies a non-empty value.

To get the behavior before Postfix version 2.2, specify "local_header_rewrite_clients = static:all".

application_event_drain_time (default: 100s)
How long the postkick(1) command waits for a request to enter the server's input buffer before giving
up.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

This feature is available in Postfix 2.1 and later.

authorized_flush_users (default: static:anyone)
List of users who are authorized to flush the queue.

By default, all users are allowed to flush the queue. Access is always granted if the invoking user
is the super-user or the $mail_owner user. Otherwise, the real UID of the process is looked up in
the system password file, and access is granted only if the corresponding login name is on the access
list. The username "unknown" is used for processes whose real UID is not found in the password file.

Specify a list of user names, "/file/name" or "type:table" patterns, separated by commas and/or
whitespace. The list is matched left to right, and the search stops on the first match. A
"/file/name" pattern is replaced by its contents; a "type:table" lookup table is matched when a name
matches a lookup key (the lookup result is ignored). Continue long lines by starting the next line
with whitespace. Specify "!pattern" to exclude a name from the list. The form "!/file/name" is sup-ported supported
ported only in Postfix version 2.4 and later.

This feature is available in Postfix 2.2 and later.

authorized_mailq_users (default: static:anyone)
List of users who are authorized to view the queue.

By default, all users are allowed to view the queue. Access is always granted if the invoking user
is the super-user or the $mail_owner user. Otherwise, the real UID of the process is looked up in
the system password file, and access is granted only if the corresponding login name is on the access
list. The username "unknown" is used for processes whose real UID is not found in the password file.

Specify a list of user names, "/file/name" or "type:table" patterns, separated by commas and/or
whitespace. The list is matched left to right, and the search stops on the first match. A
"/file/name" pattern is replaced by its contents; a "type:table" lookup table is matched when a name
matches a lookup key (the lookup result is ignored). Continue long lines by starting the next line
with whitespace. Specify "!pattern" to exclude a user name from the list. The form "!/file/name" is
supported only in Postfix version 2.4 and later.

This feature is available in Postfix 2.2 and later.

authorized_submit_users (default: static:anyone)
List of users who are authorized to submit mail with the sendmail(1) command (and with the privileged
postdrop(1) helper command).

By default, all users are allowed to submit mail. Otherwise, the real UID of the process is looked
up in the system password file, and access is granted only if the corresponding login name is on the
access list. The username "unknown" is used for processes whose real UID is not found in the pass-word password
word file. To deny mail submission access to all users specify an empty list.

Specify a list of user names, "/file/name" or "type:table" patterns, separated by commas and/or
whitespace. The list is matched left to right, and the search stops on the first match. A
"/file/name" pattern is replaced by its contents; a "type:table" lookup table is matched when a name
matches a lookup key (the lookup result is ignored). Continue long lines by starting the next line
with whitespace. Specify "!pattern" to exclude a user name from the list. The form "!/file/name" is
supported only in Postfix version 2.4 and later.

Example:

authorized_submit_users = !www, static:all

This feature is available in Postfix 2.2 and later.

authorized_verp_clients (default: $mynetworks)
What SMTP clients are allowed to specify the XVERP command. This command requests that mail be
delivered one recipient at a time with a per recipient return address.

By default, only trusted clients are allowed to specify XVERP.

This parameter was introduced with Postfix version 1.1. Postfix version 2.1 renamed this parameter
to smtpd_authorized_verp_clients and changed the default to none.

Specify a list of network/netmask patterns, separated by commas and/or whitespace. The mask specifies
the number of bits in the network part of a host address. You can also specify hostnames or \&.domain
names (the initial dot causes the domain to match any name below it), "/file/name" or "type:table"
patterns. A "/file/name" pattern is replaced by its contents; a "type:table" lookup table is matched
when a table entry matches a lookup string (the lookup result is ignored). Continue long lines by
starting the next line with whitespace. Specify "!pattern" to exclude an address or network block
from the list. The form "!/file/name" is supported only in Postfix version 2.4 and later.

Note: IP version 6 address information must be specified inside [] in the authorized_verp_clients
value, and in files specified with "/file/name". IP version 6 addresses contain the ":" character,
and would otherwise be confused with a "type:table" pattern.

backwards_bounce_logfile_compatibility (default: yes)
Produce additional bounce(8) logfile records that can be read by Postfix versions before 2.0. The
current and more extensible "name = value" format is needed in order to implement more sophisticated
functionality.

This feature is available in Postfix 2.1 and later.

berkeley_db_create_buffer_size (default: 16777216)
The per-table I/O buffer size for programs that create Berkeley DB hash or btree tables. Specify a
byte count.

This feature is available in Postfix 2.0 and later.

berkeley_db_read_buffer_size (default: 131072)
The per-table I/O buffer size for programs that read Berkeley DB hash or btree tables. Specify a
byte count.

This feature is available in Postfix 2.0 and later.

best_mx_transport (default: empty)
Where the Postfix SMTP client should deliver mail when it detects a "mail loops back to myself" error
condition. This happens when the local MTA is the best SMTP mail exchanger for a destination not
listed in $mydestination, $inet_interfaces, $proxy_interfaces, $virtual_alias_domains, or $vir-tual_mailbox_domains. $virtual_mailbox_domains.
tual_mailbox_domains. By default, the Postfix SMTP client returns such mail as undeliverable.

Specify, for example, "best_mx_transport = local" to pass the mail from the Postfix SMTP client to
the local(8) delivery agent. You can specify any message delivery "transport" or "transport:nexthop"
that is defined in the master.cf file. See the transport(5) manual page for the syntax and meaning of
"transport" or "transport:nexthop".

However, this feature is expensive because it ties up a Postfix SMTP client process while the
local(8) delivery agent is doing its work. It is more efficient (for Postfix) to list all hosted
domains in a table or database.

biff (default: yes)
Whether or not to use the local biff service. This service sends "new mail" notifications to users
who have requested new mail notification with the UNIX command "biff y".

For compatibility reasons this feature is on by default. On systems with lots of interactive users,
the biff service can be a performance drain. Specify "biff = no" in main.cf to disable.

body_checks (default: empty)
Optional lookup tables for content inspection as specified in the body_checks(5) manual page.

Note: with Postfix versions before 2.0, these rules inspect all content after the primary message
headers.

body_checks_size_limit (default: 51200)
How much text in a message body segment (or attachment, if you prefer to use that term) is subjected
to body_checks inspection. The amount of text is limited to avoid scanning huge attachments.

This feature is available in Postfix 2.0 and later.

bounce_notice_recipient (default: postmaster)
The recipient of postmaster notifications with the message headers of mail that Postfix did not
deliver and of SMTP conversation transcripts of mail that Postfix did not receive. This feature is
enabled with the notify_classes parameter.

bounce_queue_lifetime (default: 5d)
The maximal time a bounce message is queued before it is considered undeliverable. By default, this
is the same as the queue life time for regular mail.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is d
(days).

Specify 0 when mail delivery should be tried only once.

This feature is available in Postfix 2.1 and later.

bounce_service_name (default: bounce)
The name of the bounce(8) service. This service maintains a record of failed delivery attempts and
generates non-delivery notifications.

This feature is available in Postfix 2.0 and later.

bounce_size_limit (default: 50000)
The maximal amount of original message text that is sent in a non-delivery notification. Specify a
byte count. If you increase this limit, then you should increase the mime_nesting_limit value propor-tionally. proportionally.
tionally.

bounce_template_file (default: empty)
Pathname of a configuration file with bounce message templates. These override the built-in tem-plates templates
plates of delivery status notification (DSN) messages for undeliverable mail, for delayed mail, suc-cessful successful
cessful delivery, or delivery verification. The bounce(5) manual page describes how to edit and test
template files.

Template message body text may contain $name references to Postfix configuration parameters. The
result of $name expansion can be previewed with "postconf -b file_name" before the file is placed
into the Postfix configuration directory.

This feature is available in Postfix 2.3 and later.

broken_sasl_auth_clients (default: no)
Enable inter-operability with SMTP clients that implement an obsolete version of the AUTH command
(RFC 2554). Examples of such clients are MicroSoft Outlook Express version 4 and MicroSoft Exchange
version 5.0.

Specify "broken_sasl_auth_clients = yes" to have Postfix advertise AUTH support in a non-standard
way.

canonical_classes (default: envelope_sender, envelope_recipient, header_sender, header_recipient)
What addresses are subject to canonical_maps address mapping. By default, canonical_maps address
mapping is applied to envelope sender and recipient addresses, and to header sender and header recip-ient recipient
ient addresses.

Specify one or more of: envelope_sender, envelope_recipient, header_sender, header_recipient

This feature is available in Postfix 2.2 and later.

canonical_maps (default: empty)
Optional address mapping lookup tables for message headers and envelopes. The mapping is applied to
both sender and recipient addresses, in both envelopes and in headers, as controlled with the canoni-cal_classes canonical_classes
cal_classes parameter. This is typically used to clean up dirty addresses from legacy mail systems,
or to replace login names by Firstname.Lastname. The table format and lookups are documented in
canonical(5). For an overview of Postfix address manipulations see the ADDRESS_REWRITING_README docu-ment. document.
ment.

If you use this feature, run "postmap /etc/postfix/canonical" to build the necessary DBM or DB file
after every change. The changes will become visible after a minute or so. Use "postfix reload" to
eliminate the delay.

Note: with Postfix version 2.2, message header address mapping happens only when message header
address rewriting is enabled:

The message is received with the Postfix sendmail(1) command,

The message is received from a network client that matches $local_header_rewrite_clients,

The message is received from the network, and the remote_header_rewrite_domain parameter spec-ifies specifies
ifies a non-empty value.

To get the behavior before Postfix version 2.2, specify "local_header_rewrite_clients = static:all".

Examples:

canonical_maps = dbm:/etc/postfix/canonical
canonical_maps = hash:/etc/postfix/canonical

cleanup_service_name (default: cleanup)
The name of the cleanup(8) service. This service rewrites addresses into the standard form, and per-forms performs
forms canonical(5) address mapping and virtual(5) aliasing.

This feature is available in Postfix 2.0 and later.

command_directory (default: see postconf -d output)
The location of all postfix administrative commands.

command_execution_directory (default: empty)
The local(8) delivery agent working directory for delivery to external command. Failure to change
directory causes the delivery to be deferred.

The following $name expansions are done on command_execution_directory before the directory is
changed. Expansion happens in the context of the delivery request. The result of $name expansion is
filtered with the character set that is specified with the execution_directory_expansion_filter
parameter.

$user The recipient's username.

$shell The recipient's login shell pathname.

$home The recipient's home directory.

$recipient
The full recipient address.

$extension
The optional recipient address extension.

$domain
The recipient domain.

$local The entire recipient localpart.

$recipient_delimiter
The system-wide recipient address extension delimiter.

${name?value}
Expands to value when $name is non-empty.

${name:value}
Expands to value when $name is empty.

Instead of $name you can also specify ${name} or $(name).

This feature is available in Postfix 2.2 and later.

command_expansion_filter (default: see postconf -d output)
Restrict the characters that the local(8) delivery agent allows in $name expansions of $mailbox_com-mand. $mailbox_command.
mand. Characters outside the allowed set are replaced by underscores.

command_time_limit (default: 1000s)
Time limit for delivery to external commands. This limit is used by the local(8) delivery agent, and
is the default time limit for delivery by the pipe(8) delivery agent.

Note: if you set this time limit to a large value you must update the global ipc_timeout parameter as
well.

config_directory (default: see postconf -d output)
The default location of the Postfix main.cf and master.cf configuration files. This can be overruled
via the following mechanisms:

The MAIL_CONFIG environment variable (daemon processes and commands).

The "-c" command-line option (commands only).

With Postfix command that run with set-gid privileges, a config_directory override requires either
root privileges, or it requires that the directory is listed with the alternate_config_directories
parameter in the default main.cf file.

connection_cache_protocol_timeout (default: 5s)
Time limit for connection cache connect, send or receive operations. The time limit is enforced in
the client.

This feature is available in Postfix 2.3 and later.

connection_cache_service (default: scache)
The name of the scache(8) connection cache service. This service maintains a limited pool of cached
sessions.

connection_cache_status_update_time (default: 600s)
How frequently the scache(8) server logs usage statistics with connection cache hit and miss rates
for logical destinations and for physical endpoints.

connection_cache_ttl_limit (default: 2s)
The maximal time-to-live value that the scache(8) connection cache server allows. Requests that spec-ify specify
ify a larger TTL will be stored with the maximum allowed TTL. The purpose of this additional control
is to protect the infrastructure against careless people. The cache TTL is already bounded by
$max_idle.

content_filter (default: empty)
The name of a mail delivery transport that filters mail after it is queued.

This parameter uses the same syntax as the right-hand side of a Postfix transport(5) table. This set-ting setting
ting has a lower precedence than a content filter that is specified with an access(5) table or in a
header_checks(5) or body_checks(5) table.

daemon_directory (default: see postconf -d output)
The directory with Postfix support programs and daemon programs. These should not be invoked
directly by humans. The directory must be owned by root.

daemon_timeout (default: 18000s)
How much time a Postfix daemon process may take to handle a request before it is terminated by a
built-in watchdog timer.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

debug_peer_level (default: 2)
The increment in verbose logging level when a remote client or server matches a pattern in the
debug_peer_list parameter.

debug_peer_list (default: empty)
Optional list of remote client or server hostname or network address patterns that cause the verbose
logging level to increase by the amount specified in $debug_peer_level.

Specify domain names, network/netmask patterns, "/file/name" patterns or "type:table" lookup tables.
The right-hand side result from "type:table" lookups is ignored.

Pattern matching of domain names is controlled by the parent_domain_matches_subdomains parameter.

Examples:

debug_peer_list = 127.0.0.1
debug_peer_list = some.domain

debugger_command (default: empty)
The external command to execute when a Postfix daemon program is invoked with the -D option.

Use "command .. & sleep 5" so that the debugger can attach before the process marches on. If you use
an X-based debugger, be sure to set up your XAUTHORITY environment variable before starting Postfix.

Example:

debugger_command =
PATH=/usr/bin:/usr/X11R6/bin
xxgdb $daemon_directory/$process_name $process_id & sleep 5

default_database_type (default: see postconf -d output)
The default database type for use in newaliases(1), postalias(1) and postmap(1) commands. On many
UNIX systems the default type is either dbm or hash. The default setting is frozen when the Postfix
system is built.

Examples:

default_database_type = hash
default_database_type = dbm

default_delivery_slot_cost (default: 5)
How often the Postfix queue manager's scheduler is allowed to preempt delivery of one message with
another.

Each transport maintains a so-called "available delivery slot counter" for each message. One message
can be preempted by another one when the other message can be delivered using no more delivery slots
(i.e., invocations of delivery agents) than the current message counter has accumulated (or will
eventually accumulate - see about slot loans below). This parameter controls how often is the counter
incremented - it happens after each default_delivery_slot_cost recipients have been delivered.

The cost of 0 is used to disable the preempting scheduling completely. The minimum value the sched-uling scheduling
uling algorithm can use is 2 - use it if you want to maximize the message throughput rate. Although
there is no maximum, it doesn't make much sense to use values above say 50.

The only reason why the value of 2 is not the default is the way this parameter affects the delivery
of mailing-list mail. In the worst case, their delivery can take somewhere between (cost+1/cost) and
(cost/cost-1) times more than if the preemptive scheduler was disabled. The default value of 5 turns
out to provide reasonable message response times while making sure the mailing-list deliveries are
not extended by more than 20-25 percent even in the worst case.

Examples:

default_delivery_slot_cost = 0
default_delivery_slot_cost = 2

default_delivery_slot_discount (default: 50)
The default value for transport-specific _delivery_slot_discount settings.

This parameter speeds up the moment when a message preemption can happen. Instead of waiting until
the full amount of delivery slots required is available, the preemption can happen when trans-port_delivery_slot_discount transport_delivery_slot_discount
port_delivery_slot_discount percent of the required amount plus transport_delivery_slot_loan still
remains to be accumulated. Note that the full amount will still have to be accumulated before
another preemption can take place later.

default_delivery_slot_loan (default: 3)
The default value for transport-specific _delivery_slot_loan settings.

default_destination_concurrency_limit (default: 20)
The default maximal number of parallel deliveries to the same destination. This is the default limit
for delivery via the lmtp(8), pipe(8), smtp(8) and virtual(8) delivery agents.

default_destination_recipient_limit (default: 50)
The default maximal number of recipients per message delivery. This is the default limit for deliv-ery delivery
ery via the lmtp(8), pipe(8), smtp(8) and virtual(8) delivery agents.

Setting this parameter to a value of 1 changes the meaning of the corresponding per-destination con-currency concurrency
currency limit from concurrency per domain into concurrency per recipient.

default_extra_recipient_limit (default: 1000)
The default value for the extra per-transport limit imposed on the number of in-memory recipients.
This extra recipient space is reserved for the cases when the Postfix queue manager's scheduler pre-empts preempts
empts one message with another and suddenly needs some extra recipients slots for the chosen message
in order to avoid performance degradation.

default_minimum_delivery_slots (default: 3)
How many recipients a message must have in order to invoke the Postfix queue manager's scheduling
algorithm at all. Messages which would never accumulate at least this many delivery slots (subject
to slot cost parameter as well) are never preempted.

default_privs (default: nobody)
The default rights used by the local(8) delivery agent for delivery to external file or command.
These rights are used when delivery is requested from an aliases(5) file that is owned by root, or
when delivery is done on behalf of root. DO NOT SPECIFY A PRIVILEGED USER OR THE POSTFIX OWNER.

default_process_limit (default: 100)
The default maximal number of Postfix child processes that provide a given service. This limit can be
overruled for specific services in the master.cf file.

default_rbl_reply (default: see postconf -d output)
The default SMTP server response template for a request that is rejected by an RBL-based restriction.
This template can be overruled by specific entries in the optional rbl_reply_maps lookup table.

This feature is available in Postfix 2.0 and later.

The template is subject to exactly one level of $name substitution:

$client
The client hostname and IP address, formatted as name[address].

$client_address
The client IP address.

$client_name
The client hostname or "unknown". See reject_unknown_client_hostname for more details.

$reverse_client_name
The client hostname from address->name lookup, or "unknown". See
reject_unknown_reverse_client_hostname for more details.

$helo_name
The hostname given in HELO or EHLO command or empty string.

$rbl_class
The blacklisted entity type: Client host, Helo command, Sender address, or Recipient address.

$rbl_code
The numerical SMTP response code, as specified with the maps_rbl_reject_code configuration
parameter. Note: The numerical SMTP response code is required, and must appear at the start of
the reply. With Postfix version 2.3 and later this information may be followed by an RFC 3463
enhanced status code.

$rbl_domain
The RBL domain where $rbl_what is blacklisted.

$rbl_reason
The reason why $rbl_what is blacklisted, or an empty string.

$rbl_what
The entity that is blacklisted (an IP address, a hostname, a domain name, or an email address
whose domain was blacklisted).

$recipient
The recipient address or <> in case of the null address.

$recipient_domain
The recipient domain or empty string.

$recipient_name
The recipient address localpart or <> in case of null address.

$sender
The sender address or <> in case of the null address.

$sender_domain
The sender domain or empty string.

$sender_name
The sender address localpart or <> in case of the null address.

${name?text}
Expands to `text' if $name is not empty.

${name:text}
Expands to `text' if $name is empty.

Instead of $name you can also specify ${name} or $(name).

Note: when an enhanced status code is specified in an RBL reply template, it is subject to modifica-tion. modification.
tion. The following transformations are needed when the same RBL reply template is used for client,
helo, sender, or recipient access restrictions.

When rejecting a sender address, the Postfix SMTP server will transform a recipient DSN status
(e.g., 4.1.1-4.1.6) into the corresponding sender DSN status, and vice versa.

When rejecting non-address information (such as the HELO command argument or the client host-name/address), hostname/address),
name/address), the Postfix SMTP server will transform a sender or recipient DSN status into a
generic non-address DSN status (e.g., 4.0.0).

default_recipient_limit (default: 20000)
The default per-transport upper limit on the number of in-memory recipients. These limits take pri-ority priority
ority over the global qmgr_message_recipient_limit after the message has been assigned to the respec-tive respective
tive transports. See also default_extra_recipient_limit and qmgr_message_recipient_minimum.

default_recipient_refill_delay (default: 5s)
The default per-transport maximum delay between recipients refills. When not all message recipients
fit into the memory at once, keep loading more of them at least once every this many seconds. This
is used to make sure the recipients are refilled in timely manner even when $default_recipi-ent_refill_limit $default_recipient_refill_limit
ent_refill_limit is too high for too slow deliveries.

default_recipient_refill_limit (default: 100)
The default per-transport limit on the number of recipients refilled at once. When not all message
recipients fit into the memory at once, keep loading more of them in batches of at least this many at
a time. See also $default_recipient_refill_delay, which may result in recipient batches lower than
this when this limit is too high for too slow deliveries.

default_transport (default: smtp)
The default mail delivery transport and next-hop destination for destinations that do not match
$mydestination, $inet_interfaces, $proxy_interfaces, $virtual_alias_domains, $virtual_mail-box_domains, $virtual_mailbox_domains,
box_domains, or $relay_domains. In order of decreasing precedence, the nexthop destination is taken
from $default_transport, $sender_dependent_relayhost_maps, $relayhost, or from the recipient domain.
This information can be overruled with the transport(5) table.

Specify a string of the form transport:nexthop, where transport is the name of a mail delivery trans-port transport
port defined in master.cf. The :nexthop part is optional. For more details see the transport(5)
manual page.

Example:

default_transport = uucp:relayhostname

default_verp_delimiters (default: +=)
The two default VERP delimiter characters. These are used when no explicit delimiters are specified
with the SMTP XVERP command or with the "sendmail -V" command-line option. Specify characters that
are allowed by the verp_delimiter_filter setting.

This feature is available in Postfix 1.1 and later.

defer_code (default: 450)
The numerical Postfix SMTP server response code when a remote SMTP client request is rejected by the
"defer" restriction.

Do not change this unless you have a complete understanding of RFC 821.

defer_service_name (default: defer)
The name of the defer service. This service is implemented by the bounce(8) daemon and maintains a
record of failed delivery attempts and generates non-delivery notifications.

This feature is available in Postfix 2.0 and later.

defer_transports (default: empty)
The names of message delivery transports that should not deliver mail unless someone issues "sendmail
-q" or equivalent. Specify zero or more names of mail delivery transports names that appear in the
first field of master.cf.

Example:

defer_transports = smtp

delay_logging_resolution_limit (default: 2)
The maximal number of digits after the decimal point when logging sub-second delay values. Specify a
number in the range 0..6.

Large delay values are rounded off to an integral number seconds; delay values below the delay_log-ging_resolution_limit delay_logging_resolution_limit
ging_resolution_limit are logged as "0", and small delay values are logged with at most two-digit
precision.

The format of the "delays=a/b/c/d" logging is as follows:

a = time from message arrival to last active queue entry

b = time from last active queue entry to connection setup

c = time in connection setup, including DNS, EHLO and TLS

d = time in message transmission

This feature is available in Postfix 2.3 and later.

delay_notice_recipient (default: postmaster)
The recipient of postmaster notifications with the message headers of mail that cannot be delivered
within $delay_warning_time time units.

This feature is enabled with the delay_warning_time parameter.

delay_warning_time (default: 0h)
The time after which the sender receives the message headers of mail that is still queued.

To enable this feature, specify a non-zero time value (an integral value plus an optional one-letter
suffix that specifies the time unit).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is h
(hours).

deliver_lock_attempts (default: 20)
The maximal number of attempts to acquire an exclusive lock on a mailbox file or bounce(8) logfile.

deliver_lock_delay (default: 1s)
The time between attempts to acquire an exclusive lock on a mailbox file or bounce(8) logfile.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

disable_dns_lookups (default: no)
Disable DNS lookups in the Postfix SMTP and LMTP clients. When disabled, hosts are looked up with the
getaddrinfo() system library routine which normally also looks in /etc/hosts.

DNS lookups are enabled by default.

disable_mime_input_processing (default: no)
Turn off MIME processing while receiving mail. This means that no special treatment is given to Con-tent-Type: Content-Type:
tent-Type: message headers, and that all text after the initial message headers is considered to be
part of the message body.

This feature is available in Postfix 2.0 and later.

Mime input processing is enabled by default, and is needed in order to recognize MIME headers in mes-sage message
sage content.

disable_mime_output_conversion (default: no)
Disable the conversion of 8BITMIME format to 7BIT format. Mime output conversion is needed when the
destination does not advertise 8BITMIME support.

This feature is available in Postfix 2.0 and later.

disable_verp_bounces (default: no)
Disable sending one bounce report per recipient.

The default, one per recipient, is what ezmlm needs.

This feature is available in Postfix 1.1 and later.

disable_vrfy_command (default: no)
Disable the SMTP VRFY command. This stops some techniques used to harvest email addresses.

Example:

disable_vrfy_command = no

dont_remove (default: 0)
Don't remove queue files and save them to the "saved" mail queue. This is a debugging aid. To
inspect the envelope information and content of a Postfix queue file, use the postcat(1) command.

double_bounce_sender (default: double-bounce)
The sender address of postmaster notifications that are generated by the mail system. All mail to
this address is silently discarded, in order to terminate mail bounce loops.

duplicate_filter_limit (default: 1000)
The maximal number of addresses remembered by the address duplicate filter for aliases(5) or vir-tual(5) virtual(5)
tual(5) alias expansion, or for showq(8) queue displays.

empty_address_recipient (default: MAILER-DAEMON)
The recipient of mail addressed to the null address. Postfix does not accept such addresses in SMTP
commands, but they may still be created locally as the result of configuration or software error.

enable_errors_to (default: no)
Report mail delivery errors to the address specified with the non-standard Errors-To: message header,
instead of the envelope sender address (this feature is removed with Postfix version 2.2, is turned
off by default with Postfix version 2.1, and is always turned on with older Postfix versions).

enable_original_recipient (default: yes)
Enable support for the X-Original-To message header. This header is needed for multi-recipient mail-boxes. mailboxes.
boxes.

When this parameter is set to yes, the cleanup(8) daemon performs duplicate elimination on distinct
pairs of (original recipient, rewritten recipient), and generates non-empty original recipient queue
file records.

When this parameter is set to no, the cleanup(8) daemon performs duplicate elimination on the rewrit-ten rewritten
ten recipient address only, and generates empty original recipient queue file records.

This feature is available in Postfix 2.1 and later. With Postfix version 2.0, support for the X-Orig-inal-To X-Original-To
inal-To message header is always turned on. Postfix versions before 2.0 have no support for the X-Original-To XOriginal-To
Original-To message header.

error_notice_recipient (default: postmaster)
The recipient of postmaster notifications about mail delivery problems that are caused by policy,
resource, software or protocol errors. These notifications are enabled with the notify_classes
parameter.

error_service_name (default: error)
The name of the error(8) pseudo delivery agent. This service always returns mail as undeliverable.

This feature is available in Postfix 2.0 and later.

execution_directory_expansion_filter (default: see postconf -d output)
Restrict the characters that the local(8) delivery agent allows in $name expansions of $command_exe-cution_directory. $command_execution_directory.
cution_directory. Characters outside the allowed set are replaced by underscores.

This feature is available in Postfix 2.2 and later.

expand_owner_alias (default: no)
When delivering to an alias "aliasname" that has an "owner-aliasname" companion alias, set the enve-lope envelope
lope sender address to the expansion of the "owner-aliasname" alias. Normally, Postfix sets the enve-lope envelope
lope sender address to the name of the "owner-aliasname" alias.

export_environment (default: see postconf -d output)
The list of environment variables that a Postfix process will export to non-Postfix processes. The TZ
variable is needed for sane time keeping on System-V-ish systems.

Specify a list of names and/or name=value pairs, separated by whitespace or comma. The name=value
form is supported with Postfix version 2.1 and later.

Example:

export_environment = TZ PATH=/bin:/usr/bin

extract_recipient_limit (default: 10240)
The maximal number of recipient addresses that Postfix will extract from message headers when mail is
submitted with "sendmail -t".

This feature was removed in Postfix version 2.1.

fallback_relay (default: empty)
Optional list of relay hosts for SMTP destinations that can't be found or that are unreachable. With
Postfix 2.3 this parameter is renamed to smtp_fallback_relay.

By default, mail is returned to the sender when a destination is not found, and delivery is deferred
when a destination is unreachable.

The fallback relays must be SMTP destinations. Specify a domain, host, host:port, [host]:port,
[address] or [address]:port; the form [host] turns off MX lookups. If you specify multiple SMTP des-tinations, destinations,
tinations, Postfix will try them in the specified order.

Note: before Postfix 2.2, do not use the fallback_relay feature when relaying mail for a backup or
primary MX domain. Mail would loop between the Postfix MX host and the fallback_relay host when the
final destination is unavailable.

In main.cf specify "relay_transport = relay",

In master.cf specify "-o fallback_relay =" (i.e., empty) at the end of the relay entry.

In transport maps, specify "relay:nexthop..." as the right-hand side for backup or primary MX
domain entries.

Postfix version 2.2 and later will not use the fallback_relay feature for destinations that it is MX
host for.

fallback_transport (default: empty)
Optional message delivery transport that the local(8) delivery agent should use for names that are
not found in the aliases(5) or UNIX password database.

The precedence of local(8) delivery features from high to low is: aliases, .forward files, mail-box_transport_maps, mailbox_transport_maps,
box_transport_maps, mailbox_transport, mailbox_command_maps, mailbox_command, home_mailbox,
mail_spool_directory, fallback_transport_maps, fallback_transport and luser_relay.

fallback_transport_maps (default: empty)
Optional lookup tables with per-recipient message delivery transports for recipients that the
local(8) delivery agent could not find in the aliases(5) or UNIX password database.

For safety reasons, this feature does not allow $number substitutions in regular expression maps.

This feature is available in Postfix 2.3 and later.

fast_flush_domains (default: $relay_domains)
Optional list of destinations that are eligible for per-destination logfiles with mail that is queued
to those destinations.

By default, Postfix maintains "fast flush" logfiles only for destinations that the Postfix SMTP
server is willing to relay to (i.e. the default is: "fast_flush_domains = $relay_domains"; see the
relay_domains parameter in the postconf(5) manual).

Specify a list of hosts or domains, "/file/name" patterns or "type:table" lookup tables, separated by
commas and/or whitespace. Continue long lines by starting the next line with whitespace. A
"/file/name" pattern is replaced by its contents; a "type:table" lookup table is matched when the
domain or its parent domain appears as lookup key.

Specify "fast_flush_domains =" (i.e., empty) to disable the feature altogether.

fast_flush_purge_time (default: 7d)
The time after which an empty per-destination "fast flush" logfile is deleted.

You can specify the time as a number, or as a number followed by a letter that indicates the time
unit: s=seconds, m=minutes, h=hours, d=days, w=weeks. The default time unit is days.

fast_flush_refresh_time (default: 12h)
The time after which a non-empty but unread per-destination "fast flush" logfile needs to be
refreshed. The contents of a logfile are refreshed by requesting delivery of all messages listed in
the logfile.

You can specify the time as a number, or as a number followed by a letter that indicates the time
unit: s=seconds, m=minutes, h=hours, d=days, w=weeks. The default time unit is hours.

fault_injection_code (default: 0)
Force specific internal tests to fail, to test the handling of errors that are difficult to reproduce
otherwise.

flush_service_name (default: flush)
The name of the flush(8) service. This service maintains per-destination logfiles with the queue file
names of mail that is queued for those destinations.

This feature is available in Postfix 2.0 and later.

fork_attempts (default: 5)
The maximal number of attempts to fork() a child process.

fork_delay (default: 1s)
The delay between attempts to fork() a child process.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

forward_expansion_filter (default: see postconf -d output)
Restrict the characters that the local(8) delivery agent allows in $name expansions of $forward_path.
Characters outside the allowed set are replaced by underscores.

forward_path (default: see postconf -d output)
The local(8) delivery agent search list for finding a .forward file with user-specified delivery
methods. The first file that is found is used.

The following $name expansions are done on forward_path before the search actually happens. The
result of $name expansion is filtered with the character set that is specified with the for-ward_expansion_filter forward_expansion_filter
ward_expansion_filter parameter.

$user The recipient's username.

$shell The recipient's login shell pathname.

$home The recipient's home directory.

$recipient
The full recipient address.

$extension
The optional recipient address extension.

$domain
The recipient domain.

$local The entire recipient localpart.

$recipient_delimiter
The system-wide recipient address extension delimiter.

${name?value}
Expands to value when $name is non-empty.

${name:value}
Expands to value when $name is empty.

Instead of $name you can also specify ${name} or $(name).

Examples:

forward_path = /var/forward/$user
forward_path =
/var/forward/$user/.forward$recipient_delimiter$extension,
/var/forward/$user/.forward

frozen_delivered_to (default: yes)
Update the local(8) delivery agent's idea of the Delivered-To: address (see prepend_delivered_header)
only once, at the start of a delivery attempt; do not update the Delivered-To: address while expand-ing expanding
ing aliases or .forward files.

This feature is available in Postfix 2.3 and later. With older Postfix releases, the behavior is as
if this parameter is set to "no". The old setting can be expensive with deeply nested aliases or
.forward files. When an alias or .forward file changes the Delivered-To: address, it ties up one
queue file and one cleanup process instance while mail is being forwarded.

hash_queue_depth (default: 1)
The number of subdirectory levels for queue directories listed with the hash_queue_names parameter.

After changing the hash_queue_names or hash_queue_depth parameter, execute the command "postfix
reload".

hash_queue_names (default: deferred, defer)
The names of queue directories that are split across multiple subdirectory levels.

Before Postfix version 2.2, the default list of hashed queues was significantly larger. Claims about
improvements in file system technology suggest that hashing of the incoming and active queues is no
longer needed. Fewer hashed directories speed up the time needed to restart Postfix.

After changing the hash_queue_names or hash_queue_depth parameter, execute the command "postfix
reload".

header_address_token_limit (default: 10240)
The maximal number of address tokens are allowed in an address message header. Information that
exceeds the limit is discarded. The limit is enforced by the cleanup(8) server.

header_checks (default: empty)
Optional lookup tables for content inspection of primary non-MIME message headers, as specified in
the header_checks(5) manual page.

header_size_limit (default: 102400)
The maximal amount of memory in bytes for storing a message header. If a header is larger, the
excess is discarded. The limit is enforced by the cleanup(8) server.

helpful_warnings (default: yes)
Log warnings about problematic configuration settings, and provide helpful suggestions.

This feature is available in Postfix 2.0 and later.

home_mailbox (default: empty)
Optional pathname of a mailbox file relative to a local(8) user's home directory.

Specify a pathname ending in "/" for qmail-style delivery.

Examples:

home_mailbox = Mailbox
home_mailbox = Maildir/

hopcount_limit (default: 50)
The maximal number of Received: message headers that is allowed in the primary message headers. A
message that exceeds the limit is bounced, in order to stop a mailer loop.

html_directory (default: see postconf -d output)
The location of Postfix HTML files that describe how to build, configure or operate a specific Post-fix Postfix
fix subsystem or feature.

ignore_mx_lookup_error (default: no)
Ignore DNS MX lookups that produce no response. By default, the Postfix SMTP client defers delivery
and tries again after some delay. This behavior is required by the SMTP standard.

Specify "ignore_mx_lookup_error = yes" to force a DNS A record lookup instead. This violates the SMTP
standard and can result in mis-delivery of mail.

import_environment (default: see postconf -d output)
The list of environment parameters that a Postfix process will import from a non-Postfix parent
process. Examples of relevant parameters:

TZ Needed for sane time keeping on most System-V-ish systems.

DISPLAY
Needed for debugging Postfix daemons with an X-windows debugger.

XAUTHORITY
Needed for debugging Postfix daemons with an X-windows debugger.

MAIL_CONFIG
Needed to make "postfix -c" work.

Specify a list of names and/or name=value pairs, separated by whitespace or comma. The name=value
form is supported with Postfix version 2.1 and later.

in_flow_delay (default: 1s)
Time to pause before accepting a new message, when the message arrival rate exceeds the message
delivery rate. This feature is turned on by default (it's disabled on SCO UNIX due to an SCO bug).

With the default 100 SMTP server process limit, "in_flow_delay = 1s" limits the mail inflow to 100
messages per second above the number of messages delivered per second.

Specify 0 to disable the feature. Valid delays are 0..10.

inet_interfaces (default: all)
The network interface addresses that this mail system receives mail on. Specify "all" to receive mail
on all network interfaces (default), and "loopback-only" to receive mail on loopback network inter-faces interfaces
faces only (Postfix version 2.2 and later). The parameter also controls delivery of mail to
user@[ip.address].

Note 1: you need to stop and start Postfix when this parameter changes.

Note 2: address information may be enclosed inside [], but this form is not required here.

When inet_interfaces specifies just one IPv4 and/or IPv6 address that is not a loopback address, the
Postfix SMTP client will use this address as the IP source address for outbound mail. Support for
IPv6 is available in Postfix version 2.2 and later.

On a multi-homed firewall with separate Postfix instances listening on the "inside" and "outside"
interfaces, this can prevent each instance from being able to reach servers on the "other side" of
the firewall. Setting smtp_bind_address to 0.0.0.0 avoids the potential problem for IPv4, and setting
smtp_bind_address6 to :: solves the problem for IPv6.

A better solution for multi-homed firewalls is to leave inet_interfaces at the default value and
instead use explicit IP addresses in the master.cf SMTP server definitions. This preserves the Post-fix Postfix
fix SMTP client's loop detection, by ensuring that each side of the firewall knows that the other IP
address is still the same host. Setting $inet_interfaces to a single IPv4 and/or IPV6 address is pri-marily primarily
marily useful with virtual hosting of domains on secondary IP addresses, when each IP address serves
a different domain (and has a different $myhostname setting).

See also the proxy_interfaces parameter, for network addresses that are forwarded to Postfix by way
of a proxy or address translator.

Examples:

inet_interfaces = all (DEFAULT)
inet_interfaces = loopback-only (Postfix version 2.2 and later)
inet_interfaces = 127.0.0.1
inet_interfaces = 127.0.0.1, [::1] (Postfix version 2.2 and later)
inet_interfaces = 192.168.1.2, 127.0.0.1

inet_protocols (default: ipv4)
The Internet protocols Postfix will attempt to use when making or accepting connections. Specify one
or more of "ipv4" or "ipv6", separated by whitespace or commas. The form "all" is equivalent to
"ipv4, ipv6" or "ipv4", depending on whether the operating system implements IPv6.

This feature is available in Postfix 2.2 and later.

Note: you MUST stop and start Postfix after changing this parameter.

On systems that pre-date IPV6_V6ONLY support (RFC 3493), an IPv6 server will also accept IPv4 connec-tions, connections,
tions, even when IPv4 is turned off with the inet_protocols parameter. On systems with IPV6_V6ONLY
support, Postfix will use separate server sockets for IPv6 and IPv4, and each will accept only con-nections connections
nections for the corresponding protocol.

When IPv4 support is enabled via the inet_protocols parameter, Postfix will to DNS type A record
lookups, and will convert IPv4-in-IPv6 client IP addresses (::ffff:1.2.3.4) to their original IPv4
form (1.2.3.4). The latter is needed on hosts that pre-date IPV6_V6ONLY support (RFC 3493).

When IPv6 support is enabled via the inet_protocols parameter, Postfix will do DNS type AAAA record
lookups.

When both IPv4 and IPv6 support are enabled, the Postfix SMTP client will attempt to connect via IPv6
before attempting to use IPv4.

Examples:

inet_protocols = ipv4 (DEFAULT)
inet_protocols = all
inet_protocols = ipv6
inet_protocols = ipv4, ipv6

initial_destination_concurrency (default: 5)
The initial per-destination concurrency level for parallel delivery to the same destination. This
limit applies to delivery via smtp(8), and via the pipe(8) and virtual(8) delivery agents.

Warning: with concurrency of 1, one bad message can be enough to block all mail to a site.

internal_mail_filter_classes (default: empty)
What categories of Postfix-generated mail are subject to before-queue content inspection by
non_smtpd_milters, header_checks and body_checks. Specify zero or more of the following, separated
by whitespace or comma.

bounce Inspect the content of delivery status notifications.

notify Inspect the content of postmaster notifications by the smtp(8) and smtpd(8) processes.

NOTE: It's generally not safe to enable content inspection of Postfix-generated email messages. The
user is warned.

This feature is available in Postfix 2.3 and later.

invalid_hostname_reject_code (default: 501)
The numerical Postfix SMTP server response code when the client HELO or EHLO command parameter is
rejected by the reject_invalid_helo_hostname restriction.

Do not change this unless you have a complete understanding of RFC 821.

ipc_idle (default: version dependent)
The time after which a client closes an idle internal communication channel. The purpose is to allow
servers to terminate voluntarily after they become idle. This is used, for example, by the address
resolving and rewriting clients.

With Postfix 2.4 the default value was reduced from 100s to 5s.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

ipc_timeout (default: 3600s)
The time limit for sending or receiving information over an internal communication channel. The pur-pose purpose
pose is to break out of deadlock situations. If the time limit is exceeded the software aborts with a
fatal error.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

ipc_ttl (default: 1000s)
The time after which a client closes an active internal communication channel. The purpose is to
allow servers to terminate voluntarily after reaching their client limit. This is used, for example,
by the address resolving and rewriting clients.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

This feature is available in Postfix 2.1 and later.

line_length_limit (default: 2048)
Upon input, long lines are chopped up into pieces of at most this length; upon delivery, long lines
are reconstructed.

lmtp_bind_address (default: empty)
The LMTP-specific version of the smtp_bind_address configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_bind_address6 (default: empty)
The LMTP-specific version of the smtp_bind_address6 configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_cache_connection (default: yes)
Keep Postfix LMTP client connections open for up to $max_idle seconds. When the LMTP client receives
a request for the same connection the connection is reused.

The effectiveness of cached connections will be determined by the number of LMTP servers in use, and
the concurrency limit specified for the LMTP client. Cached connections are closed under any of the
following conditions:

The LMTP client idle time limit is reached. This limit is specified with the Postfix max_idle
configuration parameter.

A delivery request specifies a different destination than the one currently cached.

The per-process limit on the number of delivery requests is reached. This limit is specified
with the Postfix max_use configuration parameter.

Upon the onset of another delivery request, the LMTP server associated with the current ses-sion session
sion does not respond to the RSET command.

Most of these limitations will be removed after Postfix implements a connection cache that is shared
among multiple LMTP client programs.

lmtp_cname_overrides_servername (default: yes)
The LMTP-specific version of the smtp_cname_overrides_servername configuration parameter. See there
for details.

This feature is available in Postfix 2.3 and later.

lmtp_connect_timeout (default: 0s)
The LMTP client time limit for completing a TCP connection, or zero (use the operating system built-in builtin
in time limit). When no connection can be made within the deadline, the LMTP client tries the next
address on the mail exchanger list.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

Example:

lmtp_connect_timeout = 30s

lmtp_connection_cache_destinations (default: empty)
The LMTP-specific version of the smtp_connection_cache_destinations configuration parameter. See
there for details.

This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_on_demand (default: yes)
The LMTP-specific version of the smtp_connection_cache_on_demand configuration parameter. See there
for details.

This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_time_limit (default: 2s)
The LMTP-specific version of the smtp_connection_cache_time_limit configuration parameter. See there
for details.

This feature is available in Postfix 2.3 and later.

lmtp_connection_reuse_time_limit (default: 300s)
The LMTP-specific version of the smtp_connection_reuse_time_limit configuration parameter. See there
for details.

This feature is available in Postfix 2.3 and later.

lmtp_data_done_timeout (default: 600s)
The LMTP client time limit for sending the LMTP ".", and for receiving the server response. When no
response is received within the deadline, a warning is logged that the mail may be delivered multiple
times.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

lmtp_data_init_timeout (default: 120s)
The LMTP client time limit for sending the LMTP DATA command, and for receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

lmtp_data_xfer_timeout (default: 180s)
The LMTP client time limit for sending the LMTP message content. When the connection stalls for more
than $lmtp_data_xfer_timeout the LMTP client terminates the transfer.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

lmtp_defer_if_no_mx_address_found (default: no)
The LMTP-specific version of the smtp_defer_if_no_mx_address_found configuration parameter. See
there for details.

This feature is available in Postfix 2.3 and later.

lmtp_destination_concurrency_limit (default: $default_destination_concurrency_limit)
The maximal number of parallel deliveries to the same destination via the lmtp message delivery
transport. This limit is enforced by the queue manager. The message delivery transport name is the
first field in the entry in the master.cf file.

lmtp_destination_recipient_limit (default: $default_destination_recipient_limit)
The maximal number of recipients per delivery via the lmtp message delivery transport. This limit is
enforced by the queue manager. The message delivery transport name is the first field in the entry in
the master.cf file.

Setting this parameter to a value of 1 changes the meaning of lmtp_destination_concurrency_limit from
concurrency per domain into concurrency per recipient.

lmtp_discard_lhlo_keyword_address_maps (default: empty)
Lookup tables, indexed by the remote LMTP server address, with case insensitive lists of LHLO key-words keywords
words (pipelining, starttls, auth, etc.) that the LMTP client will ignore in the LHLO response from a
remote LMTP server. See lmtp_discard_lhlo_keywords for details. The table is not indexed by hostname
for consistency with smtpd_discard_ehlo_keyword_address_maps.

This feature is available in Postfix 2.3 and later.

lmtp_discard_lhlo_keywords (default: empty)
A case insensitive list of LHLO keywords (pipelining, starttls, auth, etc.) that the LMTP client will
ignore in the LHLO response from a remote LMTP server.

This feature is available in Postfix 2.3 and later.

Notes:

Specify the silent-discard pseudo keyword to prevent this action from being logged.

Use the lmtp_discard_lhlo_keyword_address_maps feature to discard LHLO keywords selectively.

lmtp_enforce_tls (default: no)
The LMTP-specific version of the smtp_enforce_tls configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_generic_maps (default: empty)
The LMTP-specific version of the smtp_generic_maps configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_host_lookup (default: dns)
The LMTP-specific version of the smtp_host_lookup configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_lhlo_name (default: $myhostname)
The hostname to send in the LMTP LHLO command.

The default value is the machine hostname. Specify a hostname or [ip.add.re.ss].

This information can be specified in the main.cf file for all LMTP clients, or it can be specified in
the master.cf file for a specific client, for example:

/etc/postfix/master.cf:
mylmtp ... lmtp -o lmtp_lhlo_name=foo.bar.com

This feature is available in Postfix 2.3 and later.

lmtp_lhlo_timeout (default: 300s)
The LMTP client time limit for sending the LHLO command, and for receiving the initial server
response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

lmtp_line_length_limit (default: 990)
The LMTP-specific version of the smtp_line_length_limit configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_mail_timeout (default: 300s)
The LMTP client time limit for sending the MAIL FROM command, and for receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

lmtp_mx_address_limit (default: 5)
The LMTP-specific version of the smtp_mx_address_limit configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_mx_session_limit (default: 2)
The LMTP-specific version of the smtp_mx_session_limit configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_pix_workaround_delay_time (default: 10s)
The LMTP-specific version of the smtp_pix_workaround_delay_time configuration parameter. See there
for details.

This feature is available in Postfix 2.3 and later.

lmtp_pix_workaround_maps (default: empty)
The LMTP-specific version of the smtp_pix_workaround_maps configuration parameter. See there for
details.

This feature is available in Postfix 2.4 and later.

lmtp_pix_workaround_threshold_time (default: 500s)
The LMTP-specific version of the smtp_pix_workaround_threshold_time configuration parameter. See
there for details.

This feature is available in Postfix 2.3 and later.

lmtp_pix_workarounds (default: empty)
The LMTP-specific version of the smtp_pix_workaround configuration parameter. See there for details.

This feature is available in Postfix 2.4 and later.

lmtp_quit_timeout (default: 300s)
The LMTP client time limit for sending the QUIT command, and for receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

lmtp_quote_rfc821_envelope (default: yes)
The LMTP-specific version of the smtp_quote_rfc821_envelope configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_randomize_addresses (default: yes)
The LMTP-specific version of the smtp_randomize_addresses configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_rcpt_timeout (default: 300s)
The LMTP client time limit for sending the RCPT TO command, and for receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

lmtp_rset_timeout (default: 20s)
The LMTP client time limit for sending the RSET command, and for receiving the server response. The
LMTP client sends RSET in order to finish a recipient address probe, or to verify that a cached con-nection connection
nection is still alive.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

lmtp_sasl_auth_enable (default: no)
Enable SASL authentication in the Postfix LMTP client.

lmtp_sasl_mechanism_filter (default: empty)
The LMTP-specific version of the smtp_sasl_mechanism_filter configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_sasl_password_maps (default: empty)
Optional LMTP client lookup tables with one username:password entry per host or domain. If a remote
host or domain has no username:password entry, then the Postfix LMTP client will not attempt to
authenticate to the remote host.

lmtp_sasl_path (default: empty)
Implementation-specific information that is passed through to the SASL plug-in implementation that is
selected with lmtp_sasl_type. Typically this specifies the name of a configuration file or ren-dezvous rendezvous
dezvous point.

This feature is available in Postfix 2.3 and later.

lmtp_sasl_security_options (default: noplaintext, noanonymous)
SASL security options; as of Postfix 2.3 the list of available features depends on the SASL client
implementation that is selected with lmtp_sasl_type.

The following security features are defined for the cyrus client SASL implementation:

noplaintext
Disallow authentication methods that use plaintext passwords.

noactive
Disallow authentication methods that are vulnerable to non-dictionary active attacks.

nodictionary
Disallow authentication methods that are vulnerable to passive dictionary attack.

noanonymous
Disallow anonymous logins.

Example:

lmtp_sasl_security_options = noplaintext

lmtp_sasl_tls_security_options (default: $lmtp_sasl_security_options)
The LMTP-specific version of the smtp_sasl_tls_security_options configuration parameter. See there
for details.

This feature is available in Postfix 2.3 and later.

lmtp_sasl_tls_verified_security_options (default: $lmtp_sasl_tls_security_options)
The LMTP-specific version of the smtp_sasl_tls_verified_security_options configuration parameter.
See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_sasl_type (default: cyrus)
The SASL plug-in type that the Postfix LMTP client should use for authentication. The available
types are listed with the "postconf -A" command.

This feature is available in Postfix 2.3 and later.

lmtp_send_xforward_command (default: no)
Send an XFORWARD command to the LMTP server when the LMTP LHLO server response announces XFORWARD
support. This allows an lmtp(8) delivery agent, used for content filter message injection, to for-ward forward
ward the name, address, protocol and HELO name of the original client to the content filter and down-stream downstream
stream queuing LMTP server. Before you change the value to yes, it is best to make sure that your
content filter supports this command.

This feature is available in Postfix 2.1 and later.

lmtp_sender_dependent_authentication (default: no)
The LMTP-specific version of the smtp_sender_dependent_authentication configuration parameter. See
there for details.

This feature is available in Postfix 2.3 and later.

lmtp_skip_5xx_greeting (default: yes)
The LMTP-specific version of the smtp_skip_5xx_greeting configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_skip_quit_response (default: no)
Wait for the response to the LMTP QUIT command.

lmtp_starttls_timeout (default: 300s)
The LMTP-specific version of the smtp_starttls_timeout configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_tcp_port (default: 24)
The default TCP port that the Postfix LMTP client connects to.

lmtp_tls_CAfile (default: empty)
The LMTP-specific version of the smtp_tls_CAfile configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_CApath (default: empty)
The LMTP-specific version of the smtp_tls_CApath configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_cert_file (default: empty)
The LMTP-specific version of the smtp_tls_cert_file configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_dcert_file (default: empty)
The LMTP-specific version of the smtp_tls_dcert_file configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_dkey_file (default: $lmtp_tls_dcert_file)
The LMTP-specific version of the smtp_tls_dkey_file configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_enforce_peername (default: yes)
The LMTP-specific version of the smtp_tls_enforce_peername configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_exclude_ciphers (default: empty)
The LMTP-specific version of the smtp_tls_exclude_ciphers configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_key_file (default: $lmtp_tls_cert_file)
The LMTP-specific version of the smtp_tls_key_file configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_loglevel (default: 0)
The LMTP-specific version of the smtp_tls_loglevel configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_ciphers (default: empty)
The LMTP-specific version of the smtp_tls_mandatory_ciphers configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_exclude_ciphers (default: empty)
The LMTP-specific version of the smtp_tls_mandatory_exclude_ciphers configuration parameter. See
there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_protocols (default: SSLv3, TLSv1)
The LMTP-specific version of the smtp_tls_mandatory_protocols configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_note_starttls_offer (default: no)
The LMTP-specific version of the smtp_tls_note_starttls_offer configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_per_site (default: empty)
The LMTP-specific version of the smtp_tls_per_site configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_policy_maps (default: empty)
The LMTP-specific version of the smtp_tls_policy_maps configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_scert_verifydepth (default: 5)
The LMTP-specific version of the smtp_tls_scert_verifydepth configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_secure_cert_match (default: nexthop)
The LMTP-specific version of the smtp_tls_secure_cert_match configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_database (default: empty)
The LMTP-specific version of the smtp_tls_session_cache_database configuration parameter. See there
for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_timeout (default: 3600s)
The LMTP-specific version of the smtp_tls_session_cache_timeout configuration parameter. See there
for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_verify_cert_match (default: hostname)
The LMTP-specific version of the smtp_tls_verify_cert_match configuration parameter. See there for
details.

This feature is available in Postfix 2.3 and later.

lmtp_use_tls (default: no)
The LMTP-specific version of the smtp_use_tls configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_xforward_timeout (default: 300s)
The LMTP client time limit for sending the XFORWARD command, and for receiving the server response.

In case of problems the client does NOT try the next address on the mail exchanger list.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

This feature is available in Postfix 2.1 and later.

local_command_shell (default: empty)
Optional shell program for local(8) delivery to non-Postfix command. By default, non-Postfix com-mands commands
mands are executed directly; commands are given to given to /bin/sh only when they contain shell meta
characters or shell built-in commands.

"sendmail's restricted shell" (smrsh) is what most people will use in order to restrict what programs
can be run from e.g. .forward files (smrsh is part of the Sendmail distribution).

Note: when a shell program is specified, it is invoked even when the command contains no shell built-in builtin
in commands or meta characters.

Example:

local_command_shell = /some/where/smrsh -c

local_destination_concurrency_limit (default: 2)
The maximal number of parallel deliveries via the local mail delivery transport to the same recipient
(when "local_destination_recipient_limit = 1") or the maximal number of parallel deliveries to the
same local domain (when "local_destination_recipient_limit > 1"). This limit is enforced by the queue
manager. The message delivery transport name is the first field in the entry in the master.cf file.

A low limit of 2 is recommended, just in case someone has an expensive shell command in a .forward
file or in an alias (e.g., a mailing list manager). You don't want to run lots of those at the same
time.

local_destination_recipient_limit (default: 1)
The maximal number of recipients per message delivery via the local mail delivery transport. This
limit is enforced by the queue manager. The message delivery transport name is the first field in the
entry in the master.cf file.

Setting this parameter to a value > 1 changes the meaning of local_destination_concurrency_limit from
concurrency per recipient into concurrency per domain.

local_header_rewrite_clients (default: permit_inet_interfaces)
Rewrite message header addresses in mail from these clients and update incomplete addresses with the
domain name in $myorigin or $mydomain; either don't rewrite message headers from other clients at
all, or rewrite message headers and update incomplete addresses with the domain specified in the
remote_header_rewrite_domain parameter.

See the append_at_myorigin and append_dot_mydomain parameters for details of how domain names are
appended to incomplete addresses.

Specify a list of zero or more of the following:

permit_inet_interfaces
Append the domain name in $myorigin or $mydomain when the client IP address matches
$inet_interfaces. This is enabled by default.

permit_mynetworks
Append the domain name in $myorigin or $mydomain when the client IP address matches any net-work network
work or network address listed in $mynetworks. This setting will not prevent remote mail
header address rewriting when mail from a remote client is forwarded by a neighboring system.

permit_sasl_authenticated
Append the domain name in $myorigin or $mydomain when the client is successfully authenticated
via the RFC 2554 (AUTH) protocol.

permit_tls_clientcerts
Append the domain name in $myorigin or $mydomain when the client TLS certificate is success-fully successfully
fully verified, and the client certificate fingerprint is listed in $relay_clientcerts.

permit_tls_all_clientcerts
Append the domain name in $myorigin or $mydomain when the client TLS certificate is success-fully successfully
fully verified, regardless of whether it is listed on the server, and regardless of the certi-fying certifying
fying authority.

check_address_map type:table

type:table
Append the domain name in $myorigin or $mydomain when the client IP address matches the speci-fied specified
fied lookup table. The lookup result is ignored, and no subnet lookup is done. This is suit-able suitable
able for, e.g., pop-before-smtp lookup tables.

Examples:

The Postfix < 2.2 backwards compatible setting: always rewrite message headers, and always append my
own domain to incomplete header addresses.

local_header_rewrite_clients = static:all

The purist (and default) setting: rewrite headers only in mail from Postfix sendmail and in SMTP mail
from this machine.

local_header_rewrite_clients = permit_inet_interfaces

The intermediate setting: rewrite header addresses and append $myorigin or $mydomain information only
with mail from Postfix sendmail, from local clients, or from authorized SMTP clients.

Note: this setting will not prevent remote mail header address rewriting when mail from a remote
client is forwarded by a neighboring system.

local_header_rewrite_clients = permit_mynetworks,
permit_sasl_authenticated permit_tls_clientcerts
check_address_map hash:/etc/postfix/pop-before-smtp

local_recipient_maps (default: proxy:unix:passwd.byname $alias_maps)
Lookup tables with all names or addresses of local recipients: a recipient address is local when its
domain matches $mydestination, $inet_interfaces or $proxy_interfaces. Specify @domain as a wild-card
for domains that do not have a valid recipient list. Technically, tables listed with $local_recipi-
ent_maps are used as lists: Postfix needs to know only if a lookup string is found or not, but it
does not use the result from table lookup.

If this parameter is non-empty (the default), then the Postfix SMTP server will reject mail for
unknown local users.

To turn off local recipient checking in the Postfix SMTP server, specify "local_recipient_maps ="
(i.e. empty).

The default setting assumes that you use the default Postfix local delivery agent for local delivery.
You need to update the local_recipient_maps setting if:

You redefine the local delivery agent in master.cf.

You redefine the "local_transport" setting in main.cf.

You use the "luser_relay", "mailbox_transport", or "fallback_transport" feature of the Postfix
local(8) delivery agent.

Details are described in the LOCAL_RECIPIENT_README file.

Beware: if the Postfix SMTP server runs chrooted, you need to access the passwd file via the prox-ymap(8) proxymap(8)
ymap(8) service, in order to overcome chroot access restrictions. The alternative, maintaining a copy
of the system password file in the chroot jail is not practical.

Examples:

local_recipient_maps =

local_transport (default: local:$myhostname)
The default mail delivery transport and next-hop destination for final delivery to domains listed
with mydestination, and for [ipaddress] destinations that match $inet_interfaces or $proxy_inter-faces. $proxy_interfaces.
faces. This information can be overruled with the transport(5) table.

By default, local mail is delivered to the transport called "local", which is just the name of a ser-vice service
vice that is defined the master.cf file.

Beware: if you override the default local delivery agent then you need to review the LOCAL_RECIPI-ENT_README LOCAL_RECIPIENT_README
ENT_README document, otherwise the SMTP server may reject mail for local recipients.

luser_relay (default: empty)
Optional catch-all destination for unknown local(8) recipients. By default, mail for unknown recipi-ents recipients
ents in domains that match $mydestination, $inet_interfaces or $proxy_interfaces is returned as unde-liverable. undeliverable.
liverable.

The following $name expansions are done on luser_relay:

$domain
The recipient domain.

$extension
The recipient address extension.

$home The recipient's home directory.

$local The entire recipient address localpart.

$recipient
The full recipient address.

$recipient_delimiter
The system-wide recipient address extension delimiter.

$shell The recipient's login shell.

$user The recipient username.

${name?value}
Expands to value when $name has a non-empty value.

${name:value}
Expands to value when $name has an empty value.

Instead of $name you can also specify ${name} or $(name).

Note: luser_relay works only for the Postfix local(8) delivery agent.

Note: if you use this feature for accounts not in the UNIX password file, then you must specify
"local_recipient_maps =" (i.e. empty) in the main.cf file, otherwise the Postfix SMTP server will
reject mail for non-UNIX accounts with "User unknown in local recipient table".

Examples:

luser_relay = $user@other.host
luser_relay = $local@other.host
luser_relay = admin+$local

mail_name (default: Postfix)
The mail system name that is displayed in Received: headers, in the SMTP greeting banner, and in
bounced mail.

mail_owner (default: postfix)
The UNIX system account that owns the Postfix queue and most Postfix daemon processes. Specify the
name of a user account that does not share a group with other accounts and that owns no other files
or processes on the system. In particular, don't specify nobody or daemon. PLEASE USE A DEDICATED
USER ID AND GROUP ID.

When this parameter value is changed you need to re-run "postfix set-permissions" (with Postfix ver-sion version
sion 2.0 and earlier: "/etc/postfix/post-install set-permissions".

mail_release_date (default: see postconf -d output)
The Postfix release date, in "YYYYMMDD" format.

mail_spool_directory (default: see postconf -d output)
The directory where local(8) UNIX-style mailboxes are kept. The default setting depends on the system
type. Specify a name ending in / for maildir-style delivery.

Note: maildir delivery is done with the privileges of the recipient. If you use the
mail_spool_directory setting for maildir style delivery, then you must create the top-level maildir
directory in advance. Postfix will not create it.

Examples:

mail_spool_directory = /var/mail
mail_spool_directory = /var/spool/mail

mail_version (default: see postconf -d output)
The version of the mail system. Stable releases are named major.minor.patchlevel. Experimental
releases also include the release date. The version string can be used in, for example, the SMTP
greeting banner.

mailbox_command (default: empty)
Optional external command that the local(8) delivery agent should use for mailbox delivery. The com-mand command
mand is run with the user ID and the primary group ID privileges of the recipient. Exception: com-mand command
mand delivery for root executes with $default_privs privileges. This is not a problem, because 1)
mail for root should always be aliased to a real user and 2) don't log in as root, use "su" instead.

The following environment variables are exported to the command:

CLIENT_ADDRESS
Remote client network address. Available in Postfix version 2.2 and later.

CLIENT_HELO
Remote client EHLO command parameter. Available in Postfix version 2.2 and later.

CLIENT_HOSTNAME
Remote client hostname. Available in Postfix version 2.2 and later.

CLIENT_PROTOCOL
Remote client protocol. Available in Postfix version 2.2 and later.

DOMAIN The domain part of the recipient address.

EXTENSION
The optional address extension.

HOME The recipient home directory.

LOCAL The recipient address localpart.

LOGNAME
The recipient's username.

RECIPIENT
The full recipient address.

SASL_METHOD
SASL authentication method specified in the remote client AUTH command. Available in Postfix
version 2.2 and later.

SASL_SENDER
SASL sender address specified in the remote client MAIL FROM command. Available in Postfix
version 2.2 and later.

SASL_USER
SASL username specified in the remote client AUTH command. Available in Postfix version 2.2
and later.

SENDER The full sender address.

SHELL The recipient's login shell.

USER The recipient username.

Unlike other Postfix configuration parameters, the mailbox_command parameter is not subjected to
$name substitutions. This is to make it easier to specify shell syntax (see example below).

If you can, avoid shell meta characters because they will force Postfix to run an expensive shell
process. If you're delivering via Procmail then running a shell won't make a noticeable difference in
the total cost.

Note: if you use the mailbox_command feature to deliver mail system-wide, you must set up an alias
that forwards mail for root to a real user.

Examples:

mailbox_command = /some/where/procmail
mailbox_command = /some/where/procmail -a "$EXTENSION"
mailbox_command = /some/where/maildrop -d "$USER"
-f "$SENDER" "$EXTENSION"

mailbox_command_maps (default: empty)
Optional lookup tables with per-recipient external commands to use for local(8) mailbox delivery.
Behavior is as with mailbox_command.

mailbox_delivery_lock (default: see postconf -d output)
How to lock a UNIX-style local(8) mailbox before attempting delivery. For a list of available file
locking methods, use the "postconf -l" command.

This setting is ignored with maildir style delivery, because such deliveries are safe without
explicit locks.

Note: The dotlock method requires that the recipient UID or GID has write access to the parent direc-tory directory
tory of the mailbox file.

Note: the default setting of this parameter is system dependent.

mailbox_size_limit (default: 51200000)
The maximal size of any local(8) individual mailbox or maildir file, or zero (no limit). In fact,
this limits the size of any file that is written to upon local delivery, including files written by
external commands that are executed by the local(8) delivery agent.

This limit must not be smaller than the message size limit.

mailbox_transport (default: empty)
Optional message delivery transport that the local(8) delivery agent should use for mailbox delivery
to all local recipients, whether or not they are found in the UNIX passwd database.

mailbox_transport_maps (default: empty)
Optional lookup tables with per-recipient message delivery transports to use for local(8) mailbox
delivery, whether or not the recipients are found in the UNIX passwd database.

For safety reasons, this feature does not allow $number substitutions in regular expression maps.

This feature is available in Postfix 2.3 and later.

mailq_path (default: see postconf -d output)
Sendmail compatibility feature that specifies where the Postfix mailq(1) command is installed. This
command can be used to list the Postfix mail queue.

manpage_directory (default: see postconf -d output)
Where the Postfix manual pages are installed.

maps_rbl_domains (default: empty)
Obsolete feature: use the reject_rbl_client feature instead.

maps_rbl_reject_code (default: 554)
The numerical Postfix SMTP server response code when a remote SMTP client request is blocked by the
reject_rbl_client, reject_rhsbl_client, reject_rhsbl_sender or reject_rhsbl_recipient restriction.

Do not change this unless you have a complete understanding of RFC 821.

masquerade_classes (default: envelope_sender, header_sender, header_recipient)
What addresses are subject to address masquerading.

By default, address masquerading is limited to envelope sender addresses, and to header sender and
header recipient addresses. This allows you to use address masquerading on a mail gateway while
still being able to forward mail to users on individual machines.

Specify zero or more of: envelope_sender, envelope_recipient, header_sender, header_recipient

masquerade_domains (default: empty)
Optional list of domains whose subdomain structure will be stripped off in email addresses.

The list is processed left to right, and processing stops at the first match. Thus,

masquerade_domains = foo.example.com example.com

strips "user@any.thing.foo.example.com" to "user@foo.example.com", but strips
"user@any.thing.else.example.com" to "user@example.com".

A domain name prefixed with ! means do not masquerade this domain or its subdomains. Thus,

masquerade_domains = !foo.example.com example.com

does not change "user@any.thing.foo.example.com" or "user@foo.example.com", but strips
"user@any.thing.else.example.com" to "user@example.com".

Note: with Postfix version 2.2, message header address masquerading happens only when message header
address rewriting is enabled:

The message is received with the Postfix sendmail(1) command,

The message is received from a network client that matches $local_header_rewrite_clients,

The message is received from the network, and the remote_header_rewrite_domain parameter spec-ifies specifies
ifies a non-empty value.

To get the behavior before Postfix version 2.2, specify "local_header_rewrite_clients = static:all".

Example:

masquerade_domains = $mydomain

masquerade_exceptions (default: empty)
Optional list of user names that are not subjected to address masquerading, even when their address
matches $masquerade_domains.

By default, address masquerading makes no exceptions.

Examples:

masquerade_exceptions = root, mailer-daemon
masquerade_exceptions = root

max_idle (default: 100s)
The maximum amount of time that an idle Postfix daemon process waits for an incoming connection
before terminating voluntarily. This parameter is ignored by the Postfix queue manager and by other
long-lived Postfix daemon processes.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

max_use (default: 100)
The maximal number of incoming connections that a Postfix daemon process will service before termi-nating terminating
nating voluntarily. This parameter is ignored by the Postfix queue manager and by other long-lived
Postfix daemon processes.

maximal_backoff_time (default: 4000s)
The maximal time between attempts to deliver a deferred message.

This parameter should be set to a value greater than or equal to $minimal_backoff_time. See also
$queue_run_delay.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

maximal_queue_lifetime (default: 5d)
The maximal time a message is queued before it is sent back as undeliverable.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is d
(days).

Specify 0 when mail delivery should be tried only once.

message_reject_characters (default: empty)
The set of characters that Postfix will reject in message content. The usual C-like escape sequences
are recognized: \a \b \f \n \r \t \v \ddd (up to three octal digits) and \\.

Example:

message_reject_characters = \0

This feature is available in Postfix 2.3 and later.

message_size_limit (default: 10240000)
The maximal size in bytes of a message, including envelope information.

message_strip_characters (default: empty)
The set of characters that Postfix will remove from message content. The usual C-like escape
sequences are recognized: \a \b \f \n \r \t \v \ddd (up to three octal digits) and \\.

Example:

message_strip_characters = \0

This feature is available in Postfix 2.3 and later.

milter_command_timeout (default: 30s)
The time limit for sending an SMTP command to a Milter (mail filter) application, and for receiving
the response.

Specify a non-zero time value (an integral value plus an optional one-letter suffix that specifies
the time unit).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

This feature is available in Postfix 2.3 and later.

milter_connect_macros (default: see postconf -n output)
The macros that are sent to Milter (mail filter) applications after completion of an SMTP connection.
See MILTER_README for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_connect_timeout (default: 30s)
The time limit for connecting to a Milter (mail filter) application, and for negotiating protocol
options.

Specify a non-zero time value (an integral value plus an optional one-letter suffix that specifies
the time unit).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

This feature is available in Postfix 2.3 and later.

milter_content_timeout (default: 300s)
The time limit for sending message content to a Milter (mail filter) application, and for receiving
the response.

Specify a non-zero time value (an integral value plus an optional one-letter suffix that specifies
the time unit).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

This feature is available in Postfix 2.3 and later.

milter_data_macros (default: see postconf -n output)
The macros that are sent to version 4 or higher Milter (mail filter) applications after the SMTP DATA
command. See MILTER_README for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_default_action (default: tempfail)
The default action when a Milter (mail filter) application is unavailable or mis-configured. Specify
one of the following:

accept Proceed as if the mail filter was not present.

reject Reject all further commands in this session with a permanent status code.

tempfail
Reject all further commands in this session with a temporary status code.

This feature is available in Postfix 2.3 and later.

milter_end_of_data_macros (default: see postconf -n output)
The macros that are sent to Milter (mail filter) applications after the message end-of-data. See MIL-TER_README MILTER_README
TER_README for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_helo_macros (default: see postconf -n output)
The macros that are sent to Milter (mail filter) applications after the SMTP HELO or EHLO command.
See MILTER_README for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_macro_daemon_name (default: $myhostname)
The {daemon_name} macro value for Milter (mail filter) applications. See MILTER_README for a list of
available macro names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_macro_v (default: $mail_name $mail_version)
The {v} macro value for Milter (mail filter) applications. See MILTER_README for a list of available
macro names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_mail_macros (default: see postconf -n output)
The macros that are sent to Milter (mail filter) applications after the SMTP MAIL FROM command. See
MILTER_README for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_protocol (default: 2)
The mail filter protocol version and optional protocol extensions for communication with a Milter
(mail filter) application. This information should match the protocol that is expected by the actual
mail filter application.

Protocol versions:

2 Use Sendmail 8 mail filter protocol version 2.

3 Use Sendmail 8 mail filter protocol version 3.

4 Use Sendmail 8 mail filter protocol version 4.

Protocol extensions:

no_header_reply
Specify this when the Milter application will not reply for each individual message header.

This feature is available in Postfix 2.3 and later.

milter_rcpt_macros (default: see postconf -n output)
The macros that are sent to Milter (mail filter) applications after the SMTP RCPT TO command. See
MILTER_README for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_unknown_command_macros (default: see postconf -n output)
The macros that are sent to version 3 or higher Milter (mail filter) applications after an unknown
SMTP command. See MILTER_README for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.

mime_boundary_length_limit (default: 2048)
The maximal length of MIME multipart boundary strings. The MIME processor is unable to distinguish
between boundary strings that do not differ in the first $mime_boundary_length_limit characters.

This feature is available in Postfix 2.0 and later.

mime_header_checks (default: $header_checks)
Optional lookup tables for content inspection of MIME related message headers, as described in the
header_checks(5) manual page.

This feature is available in Postfix 2.0 and later.

mime_nesting_limit (default: 100)
The maximal recursion level that the MIME processor will handle. Postfix refuses mail that is nested
deeper than the specified limit.

This feature is available in Postfix 2.0 and later.

minimal_backoff_time (default: 300s)
The minimal time between attempts to deliver a deferred message; prior to Postfix 2.4 the default
value was 1000s.

This parameter also limits the time an unreachable destination is kept in the short-term, in-memory,
destination status cache.

This parameter should be set greater than or equal to $queue_run_delay. See also $maximal_back-off_time. $maximal_backoff_time.
off_time.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

multi_recipient_bounce_reject_code (default: 550)
The numerical Postfix SMTP server response code when a remote SMTP client request is blocked by the
reject_multi_recipient_bounce restriction.

Do not change this unless you have a complete understanding of RFC 821.

This feature is available in Postfix 2.1 and later.

mydestination (default: $myhostname, localhost.$mydomain, localhost)
The list of domains that are delivered via the $local_transport mail delivery transport. By default
this is the Postfix local(8) delivery agent which looks up all recipients in /etc/passwd and
/etc/aliases. The SMTP server validates recipient addresses with $local_recipient_maps and rejects
non-existent recipients. See also the local domain class in the ADDRESS_CLASS_README file.

The default mydestination value specifies names for the local machine only. On a mail domain gate-way, gateway,
way, you should also include $mydomain.

The $local_transport delivery method is also selected for mail addressed to
user@[the.net.work.address] of the mail system (the IP addresses specified with the inet_interfaces
and proxy_interfaces parameters).

Warnings:

Do not specify the names of virtual domains - those domains are specified elsewhere. See VIR-TUAL_README VIRTUAL_README
TUAL_README for more information.

Do not specify the names of domains that this machine is backup MX host for. See STANDARD_CON-FIGURATION_README STANDARD_CONFIGURATION_README
FIGURATION_README for how to set up backup MX hosts.

By default, the Postfix SMTP server rejects mail for recipients not listed with the
local_recipient_maps parameter. See the postconf(5) manual for a description of the
local_recipient_maps and unknown_local_recipient_reject_code parameters.

Examples:

mydestination = $myhostname, localhost.$mydomain $mydomain
mydestination = $myhostname, localhost.$mydomain www.$mydomain, ftp.$mydomain

mydomain (default: see postconf -d output)
The internet domain name of this mail system. The default is to use $myhostname minus the first com-ponent. component.
ponent. $mydomain is used as a default value for many other configuration parameters.

Example:

mydomain = domain.tld

myhostname (default: see postconf -d output)
The internet hostname of this mail system. The default is to use the fully-qualified domain name from
gethostname(). $myhostname is used as a default value for many other configuration parameters.

Example:

myhostname = host.domain.tld

mynetworks (default: see postconf -d output)
The list of "trusted" SMTP clients that have more privileges than "strangers".

In particular, "trusted" SMTP clients are allowed to relay mail through Postfix. See the
smtpd_recipient_restrictions parameter description in the postconf(5) manual.

You can specify the list of "trusted" network addresses by hand or you can let Postfix do it for you
(which is the default). See the description of the mynetworks_style parameter for more information.

If you specify the mynetworks list by hand, Postfix ignores the mynetworks_style setting.

Specify a list of network addresses or network/netmask patterns, separated by commas and/or white-space. whitespace.
space. Continue long lines by starting the next line with whitespace.

The netmask specifies the number of bits in the network part of a host address. You can also specify
"/file/name" or "type:table" patterns. A "/file/name" pattern is replaced by its contents; a
"type:table" lookup table is matched when a table entry matches a lookup string (the lookup result is
ignored).

The list is matched left to right, and the search stops on the first match. Specify "!pattern" to
exclude an address or network block from the list. The form "!/file/name" is supported only in Post-fix Postfix
fix version 2.4 and later.

Note: IP version 6 address information must be specified inside [] in the mynetworks value, and in
files specified with "/file/name". IP version 6 addresses contain the ":" character, and would oth-erwise otherwise
erwise be confused with a "type:table" pattern.

Examples:

mynetworks = 127.0.0.0/8 168.100.189.0/28
mynetworks = !192.168.0.1, 192.168.0.0/28
mynetworks = 127.0.0.0/8 168.100.189.0/28 [::1]/128 [2001:240:587::]/64
mynetworks = $config_directory/mynetworks
mynetworks = hash:/etc/postfix/network_table

mynetworks_style (default: subnet)
The method to generate the default value for the mynetworks parameter. This is the list of trusted
networks for relay access control etc.

Specify "mynetworks_style = host" when Postfix should "trust" only the local machine.

Specify "mynetworks_style = subnet" when Postfix should "trust" SMTP clients in the same IP
subnetworks as the local machine. On Linux, this works correctly only with interfaces speci-fied specified
fied with the "ifconfig" command.

Specify "mynetworks_style = class" when Postfix should "trust" SMTP clients in the same IP
class A/B/C networks as the local machine. Don't do this with a dialup site - it would cause
Postfix to "trust" your entire provider's network. Instead, specify an explicit mynetworks
list by hand, as described with the mynetworks configuration parameter.

myorigin (default: $myhostname)
The domain name that locally-posted mail appears to come from, and that locally posted mail is deliv-ered delivered
ered to. The default, $myhostname, is adequate for small sites. If you run a domain with multiple
machines, you should (1) change this to $mydomain and (2) set up a domain-wide alias database that
aliases each user to user@that.users.mailhost.

Example:

myorigin = $mydomain

nested_header_checks (default: $header_checks)
Optional lookup tables for content inspection of non-MIME message headers in attached messages, as
described in the header_checks(5) manual page.

This feature is available in Postfix 2.0 and later.

newaliases_path (default: see postconf -d output)
Sendmail compatibility feature that specifies the location of the newaliases(1) command. This command
can be used to rebuild the local(8) aliases(5) database.

non_fqdn_reject_code (default: 504)
The numerical Postfix SMTP server reply code when a client request is rejected by the
reject_non_fqdn_helo_hostname, reject_non_fqdn_sender or reject_non_fqdn_recipient restriction.

non_smtpd_milters (default: empty)
A list of Milter (mail filter) applications for new mail that does not arrive via the Postfix
smtpd(8) server. This includes local submission via the sendmail(1) command line, new mail that
arrives via the Postfix qmqpd(8) server, and old mail that is re-injected into the queue with "post-super "postsuper
super -r". See the MILTER_README document for details.

This feature is available in Postfix 2.3 and later.

notify_classes (default: resource, software)
The list of error classes that are reported to the postmaster. The default is to report only the most
serious problems. The paranoid may wish to turn on the policy (UCE and mail relaying) and protocol
error (broken mail software) reports.

NOTE: postmaster notifications may contain confidential information such as SASL passwords or message
content. It is the system administrator's responsibility to treat such information with care.

The error classes are:

bounce (also implies 2bounce)
Send the postmaster copies of the headers of bounced mail, and send transcripts of SMTP ses-sions sessions
sions when Postfix rejects mail. The notification is sent to the address specified with the
bounce_notice_recipient configuration parameter (default: postmaster).

2bounce
Send undeliverable bounced mail to the postmaster. The notification is sent to the address
specified with the 2bounce_notice_recipient configuration parameter (default: postmaster).

delay Send the postmaster copies of the headers of delayed mail. The notification is sent to the
address specified with the delay_notice_recipient configuration parameter (default: postmas-ter). postmaster).
ter).

policy Send the postmaster a transcript of the SMTP session when a client request was rejected
because of (UCE) policy. The notification is sent to the address specified with the
error_notice_recipient configuration parameter (default: postmaster).

protocol
Send the postmaster a transcript of the SMTP session in case of client or server protocol
errors. The notification is sent to the address specified with the error_notice_recipient con-figuration configuration
figuration parameter (default: postmaster).

resource
Inform the postmaster of mail not delivered due to resource problems. The notification is
sent to the address specified with the error_notice_recipient configuration parameter
(default: postmaster).

software
Inform the postmaster of mail not delivered due to software problems. The notification is
sent to the address specified with the error_notice_recipient configuration parameter
(default: postmaster).

Examples:

notify_classes = bounce, delay, policy, protocol, resource, software
notify_classes = 2bounce, resource, software

owner_request_special (default: yes)
Give special treatment to owner-listname and listname-request address localparts: don't split such
addresses when the recipient_delimiter is set to "-". This feature is useful for mailing lists.

parent_domain_matches_subdomains (default: see postconf -d output)
What Postfix features match subdomains of "domain.tld" automatically, instead of requiring an
explicit ".domain.tld" pattern. This is planned backwards compatibility: eventually, all Postfix
features are expected to require explicit ".domain.tld" style patterns when you really want to match
subdomains.

permit_mx_backup_networks (default: empty)
Restrict the use of the permit_mx_backup SMTP access feature to only domains whose primary MX hosts
match the listed networks.

pickup_service_name (default: pickup)
The name of the pickup(8) service. This service picks up local mail submissions from the Postfix
maildrop queue.

This feature is available in Postfix 2.0 and later.

plaintext_reject_code (default: 450)
The numerical Postfix SMTP server response code when a request is rejected by the reject_plain-text_session reject_plaintext_session
text_session restriction.

This feature is available in Postfix 2.3 and later.

prepend_delivered_header (default: command, file, forward)
The message delivery contexts where the Postfix local(8) delivery agent prepends a Delivered-To:
message header with the address that the mail was delivered to. This information is used for mail
delivery loop detection.

By default, the Postfix local delivery agent prepends a Delivered-To: header when forwarding mail and
when delivering to file (mailbox) and command. Turning off the Delivered-To: header when forwarding
mail is not recommended.

Specify zero or more of forward, file, or command.

Example:

prepend_delivered_header = forward

process_id (read-only)
The process ID of a Postfix command or daemon process.

process_id_directory (default: pid)
The location of Postfix PID files relative to $queue_directory. This is a read-only parameter.

process_name (read-only)
The process name of a Postfix command or daemon process.

propagate_unmatched_extensions (default: canonical, virtual)
What address lookup tables copy an address extension from the lookup key to the lookup result.

For example, with a virtual(5) mapping of "joe@domain -> joe.user", the address "joe+foo@domain"
would rewrite to "joe.user+foo".

Specify zero or more of canonical, virtual, alias, forward, include or generic. These cause address
extension propagation with canonical(5), virtual(5), and aliases(5) maps, with local(8) .forward and
:include: file lookups, and with smtp(8) generic maps, respectively.

Note: enabling this feature for types other than canonical and virtual is likely to cause problems
when mail is forwarded to other sites, especially with mail that is sent to a mailing list exploder
address.

Examples:

propagate_unmatched_extensions = canonical, virtual, alias,
forward, include
propagate_unmatched_extensions = canonical, virtual

proxy_interfaces (default: empty)
The network interface addresses that this mail system receives mail on by way of a proxy or network
address translation unit.

This feature is available in Postfix 2.0 and later.

You must specify your "outside" proxy/NAT addresses when your system is a backup MX host for other
domains, otherwise mail delivery loops will happen when the primary MX host is down.

Example:

proxy_interfaces = 1.2.3.4

proxy_read_maps (default: see postconf -d output)
The lookup tables that the proxymap(8) server is allowed to access. Table references that don't
begin with proxy: are ignored. The proxymap(8) table accesses are read-only.

This feature is available in Postfix 2.0 and later.

qmgr_clog_warn_time (default: 300s)
The minimal delay between warnings that a specific destination is clogging up the Postfix active
queue. Specify 0 to disable.

This feature is enabled with the helpful_warnings parameter.

This feature is available in Postfix 2.0 and later.

qmgr_fudge_factor (default: 100)
Obsolete feature: the percentage of delivery resources that a busy mail system will use up for deliv-ery delivery
ery of a large mailing list message.

This feature exists only in the oqmgr(8) old queue manager. The current queue manager solves the
problem in a better way.

qmgr_message_active_limit (default: 20000)
The maximal number of messages in the active queue.

qmgr_message_recipient_limit (default: 20000)
The maximal number of recipients held in memory by the Postfix queue manager, and the maximal size of
the size of the short-term, in-memory "dead" destination status cache.

qmgr_message_recipient_minimum (default: 10)
The minimal number of in-memory recipients for any message. This takes priority over any other in-memory inmemory
memory recipient limits (i.e., the global qmgr_message_recipient_limit and the per transport _recipi-ent_limit) _recipient_limit)
ent_limit) if necessary. The minimum value allowed for this parameter is 1.

qmqpd_authorized_clients (default: empty)
What clients are allowed to connect to the QMQP server port.

By default, no client is allowed to use the service. This is because the QMQP server will relay mail
to any destination.

Specify a list of client patterns. A list pattern specifies a host name, a domain name, an internet
address, or a network/mask pattern, where the mask specifies the number of bits in the network part.
When a pattern specifies a file name, its contents are substituted for the file name; when a pattern
is a "type:table" table specification, table lookup is used instead.

Patterns are separated by whitespace and/or commas. In order to reverse the result, precede a pattern
with an exclamation point (!). The form "!/file/name" is supported only in Postfix version 2.4 and
later.

Example:

qmqpd_authorized_clients = !192.168.0.1, 192.168.0.0/24

qmqpd_error_delay (default: 1s)
How long the QMQP server will pause before sending a negative reply to the client. The purpose is to
slow down confused or malicious clients.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

qmqpd_timeout (default: 300s)
The time limit for sending or receiving information over the network. If a read or write operation
blocks for more than $qmqpd_timeout seconds the QMQP server gives up and disconnects.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

queue_directory (default: see postconf -d output)
The location of the Postfix top-level queue directory. This is the root directory of Postfix daemon
processes that run chrooted.

queue_file_attribute_count_limit (default: 100)
The maximal number of (name=value) attributes that may be stored in a Postfix queue file. The limit
is enforced by the cleanup(8) server.

This feature is available in Postfix 2.0 and later.

queue_minfree (default: 0)
The minimal amount of free space in bytes in the queue file system that is needed to receive mail.
This is currently used by the SMTP server to decide if it will accept any mail at all.

By default, the Postfix version 2.1 SMTP server rejects MAIL FROM commands when the amount of free
space is less than 1.5*$message_size_limit. To specify a higher minimum free space limit, specify a
queue_minfree value that is at least 1.5*$message_size_limit.

With Postfix versions 2.0 and earlier, a queue_minfree value of zero means there is no minimum
required amount of free space.

queue_run_delay (default: 300s)
The time between deferred queue scans by the queue manager; prior to Postfix 2.4 the default value
was 1000s.

This parameter should be set less than or equal to $minimal_backoff_time. See also $maximal_back-off_time. $maximal_backoff_time.
off_time.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

queue_service_name (default: qmgr)
The name of the qmgr(8) service. This service manages the Postfix queue and schedules delivery
requests.

This feature is available in Postfix 2.0 and later.

rbl_reply_maps (default: empty)
Optional lookup tables with RBL response templates. The tables are indexed by the RBL domain name. By
default, Postfix uses the default template as specified with the default_rbl_reply configuration
parameter. See there for a discussion of the syntax of RBL reply templates.

This feature is available in Postfix 2.0 and later.

readme_directory (default: see postconf -d output)
The location of Postfix README files that describe how to build, configure or operate a specific
Postfix subsystem or feature.

receive_override_options (default: empty)
Enable or disable recipient validation, built-in content filtering, or address mapping. Typically,
these are specified in master.cf as command-line arguments for the smtpd(8), qmqpd(8) or pickup(8)
daemons.

Specify zero or more of the following options. The options override main.cf settings and are either
implemented by smtpd(8), qmqpd(8), or pickup(8) themselves, or they are forwarded to the cleanup
server.

no_unknown_recipient_checks
Do not try to reject unknown recipients (SMTP server only). This is typically specified AFTER
an external content filter.

no_address_mappings
Disable canonical address mapping, virtual alias map expansion, address masquerading, and
automatic BCC (blind carbon-copy) recipients. This is typically specified BEFORE an external
content filter.

no_header_body_checks
Disable header/body_checks. This is typically specified AFTER an external content filter.

no_milters
Disable Milter (mail filter) applications. This is typically specified AFTER an external con-tent content
tent filter.

Note: when the "BEFORE content filter" receive_override_options setting is specified in the main.cf
file, specify the "AFTER content filter" receive_override_options setting in master.cf (and vice
versa).

Examples:

receive_override_options =
no_unknown_recipient_checks, no_header_body_checks
receive_override_options = no_address_mappings

This feature is available in Postfix 2.1 and later.

recipient_bcc_maps (default: empty)
Optional BCC (blind carbon-copy) address lookup tables, indexed by recipient address. The BCC
address (multiple results are not supported) is added when mail enters from outside of Postfix.

This feature is available in Postfix 2.1 and later.

The table search order is as follows:

Look up the "user+extension@domain.tld" address including the optional address extension.

Look up the "user@domain.tld" address without the optional address extension.

Look up the "user+extension" address local part when the recipient domain equals $myorigin,
$mydestination, $inet_interfaces or $proxy_interfaces.

Look up the "user" address local part when the recipient domain equals $myorigin, $mydestina-tion, $mydestination,
tion, $inet_interfaces or $proxy_interfaces.

Look up the "@domain.tld" part.

Specify the types and names of databases to use. After change, run "postmap /etc/postfix/recipi-ent_bcc". /etc/postfix/recipient_bcc".
ent_bcc".

Note: if mail to the BCC address bounces it will be returned to the sender.

Example:

recipient_bcc_maps = hash:/etc/postfix/recipient_bcc

recipient_canonical_classes (default: envelope_recipient, header_recipient)
What addresses are subject to recipient_canonical_maps address mapping. By default, recipient_canon-ical_maps recipient_canonical_maps
ical_maps address mapping is applied to envelope recipient addresses, and to header recipient
addresses.

Specify one or more of: envelope_recipient, header_recipient

This feature is available in Postfix 2.2 and later.

recipient_canonical_maps (default: empty)
Optional address mapping lookup tables for envelope and header recipient addresses. The table format
and lookups are documented in canonical(5).

Note: $recipient_canonical_maps is processed before $canonical_maps.

Example:

recipient_canonical_maps = hash:/etc/postfix/recipient_canonical

recipient_delimiter (default: empty)
The separator between user names and address extensions (user+foo). See canonical(5), local(8),
relocated(5) and virtual(5) for the effects this has on aliases, canonical, virtual, relocated and on
.forward file lookups. Basically, the software tries user+foo and .forward+foo before trying user
and .forward.

Example:

recipient_delimiter = +

reject_code (default: 554)
The numerical Postfix SMTP server response code when a remote SMTP client request is rejected by the
"reject" restriction.

Do not change this unless you have a complete understanding of RFC 821.

relay_clientcerts (default: empty)
The list of remote SMTP client certificates for which the Postfix SMTP server will allow access with
the permit_tls_clientcerts feature. This feature does not use certificate names, because Postfix
list manipulation routines treat whitespace and some other characters as special. Instead we use
certificate fingerprints as they are difficult to fake but easy to use for lookup.

Postfix lookup tables are in the form of (key, value) pairs. Since we only need the key, the value
can be chosen freely, e.g. the name of the user or host:
D7:04:2F:A7:0B:8C:A5:21:FA:31:77:E1:41:8A:EE:80 lutzpc.at.home

Example:

relay_clientcerts = hash:/etc/postfix/relay_clientcerts

For more fine-grained control, use check_ccert_access to select an appropriate access(5) policy for
each client. See RESTRICTION_CLASS_README.

This feature is available with Postfix version 2.2.

relay_destination_concurrency_limit (default: $default_destination_concurrency_limit)
The maximal number of parallel deliveries to the same destination via the relay message delivery
transport. This limit is enforced by the queue manager. The message delivery transport name is the
first field in the entry in the master.cf file.

This feature is available in Postfix 2.0 and later.

relay_destination_recipient_limit (default: $default_destination_recipient_limit)
The maximal number of recipients per delivery via the relay message delivery transport. This limit is
enforced by the queue manager. The message delivery transport name is the first field in the entry in
the master.cf file.

Setting this parameter to a value of 1 changes the meaning of relay_destination_concurrency_limit
from concurrency per domain into concurrency per recipient.

This feature is available in Postfix 2.0 and later.

relay_domains (default: $mydestination)
What destination domains (and subdomains thereof) this system will relay mail to. Subdomain matching
is controlled with the parent_domain_matches_subdomains parameter. For details about how the
relay_domains value is used, see the description of the permit_auth_destination and
reject_unauth_destination SMTP recipient restrictions.

Domains that match $relay_domains are delivered with the $relay_transport mail delivery transport.
The SMTP server validates recipient addresses with $relay_recipient_maps and rejects non-existent
recipients. See also the relay domains address class in the ADDRESS_CLASS_README file.

Note: Postfix will not automatically forward mail for domains that list this system as their primary
or backup MX host. See the permit_mx_backup restriction in the postconf(5) manual page.

Specify a list of host or domain names, "/file/name" patterns or "type:table" lookup tables, sepa-rated separated
rated by commas and/or whitespace. Continue long lines by starting the next line with whitespace. A
"/file/name" pattern is replaced by its contents; a "type:table" lookup table is matched when a (par-ent) (parent)
ent) domain appears as lookup key. Specify "!pattern" to exclude a domain from the list. The form
"!/file/name" is supported only in Postfix version 2.4 and later.

relay_domains_reject_code (default: 554)
The numerical Postfix SMTP server response code when a client request is rejected by the
reject_unauth_destination recipient restriction.

Do not change this unless you have a complete understanding of RFC 821.

relay_recipient_maps (default: empty)
Optional lookup tables with all valid addresses in the domains that match $relay_domains. Specify
@domain as a wild-card for domains that have no valid recipient list, and become a source of
backscatter mail: Postfix accepts spam for non-existent recipients and then floods innocent people
with undeliverable mail. Technically, tables listed with $relay_recipient_maps are used as lists:
Postfix needs to know only if a lookup string is found or not, but it does not use the result from
table lookup.

If this parameter is non-empty, then the Postfix SMTP server will reject mail to unknown relay users.
This feature is off by default.

See also the relay domains address class in the ADDRESS_CLASS_README file.

Example:

relay_recipient_maps = hash:/etc/postfix/relay_recipients

This feature is available in Postfix 2.0 and later.

relay_transport (default: relay)
The default mail delivery transport and next-hop destination for remote delivery to domains listed
with $relay_domains. In order of decreasing precedence, the nexthop destination is taken from
$relay_transport, $sender_dependent_relayhost_maps, $relayhost, or from the recipient domain. This
information can be overruled with the transport(5) table.

See also the relay domains address class in the ADDRESS_CLASS_README file.

This feature is available in Postfix 2.0 and later.

relayhost (default: empty)
The next-hop destination of non-local mail; overrides non-local domains in recipient addresses. This
information is overruled with relay_transport, default_transport, sender_dependent_relayhost_maps and
with the transport(5) table.

On an intranet, specify the organizational domain name. If your internal DNS uses no MX records,
specify the name of the intranet gateway host instead.

In the case of SMTP, specify a domain name, hostname, hostname:port, [hostname]:port, [hostaddress]
or [hostaddress]:port. The form [hostname] turns off MX lookups.

If you're connected via UUCP, see the UUCP_README file for useful information.

Examples:

relayhost = $mydomain
relayhost = [gateway.my.domain]
relayhost = uucphost
relayhost = [an.ip.add.ress]

relocated_maps (default: empty)
Optional lookup tables with new contact information for users or domains that no longer exist. The
table format and lookups are documented in relocated(5).

If you use this feature, run "postmap /etc/postfix/relocated" to build the necessary DBM or DB file
after change, then "postfix reload" to make the changes visible.

Examples:

relocated_maps = dbm:/etc/postfix/relocated
relocated_maps = hash:/etc/postfix/relocated

remote_header_rewrite_domain (default: empty)
Don't rewrite message headers from remote clients at all when this parameter is empty; otherwise, re-write rewrite
write message headers and append the specified domain name to incomplete addresses. The
local_header_rewrite_clients parameter controls what clients Postfix considers local.

Examples:

The safe setting: append "domain.invalid" to incomplete header addresses from remote SMTP clients, so
that those addresses cannot be confused with local addresses.

remote_header_rewrite_domain = domain.invalid

The default, purist, setting: don't rewrite headers from remote clients at all.

remote_header_rewrite_domain =

require_home_directory (default: no)
Whether or not a local(8) recipient's home directory must exist before mail delivery is attempted. By
default this test is disabled. It can be useful for environments that import home directories to the
mail server (NOT RECOMMENDED).

resolve_dequoted_address (default: yes)
Resolve a recipient address safely instead of correctly, by looking inside quotes.

By default, the Postfix address resolver does not quote the address localpart as per RFC 822, so that
additional @ or % or ! operators remain visible. This behavior is safe but it is also technically
incorrect.

If you specify "resolve_dequoted_address = no", then the Postfix resolver will not know about addi-tional additional
tional @ etc. operators in the address localpart. This opens opportunities for obscure mail relay
attacks with user@domain@domain addresses when Postfix provides backup MX service for Sendmail sys-tems. systems.
tems.

resolve_null_domain (default: no)
Resolve an address that ends in the "@" null domain as if the local hostname were specified, instead
of rejecting the address as invalid.

This feature is available in Postfix 2.1 and later. Earlier versions always resolve the null domain
as the local hostname.

The Postfix SMTP server uses this feature to reject mail from or to addresses that end in the "@"
null domain, and from addresses that rewrite into a form that ends in the "@" null domain.

resolve_numeric_domain (default: no)
Resolve "user@ipaddress" as "user@[ipaddress]", instead of rejecting the address as invalid.

This feature is available in Postfix 2.3 and later.

rewrite_service_name (default: rewrite)
The name of the address rewriting service. This service rewrites addresses to standard form and
resolves them to a (delivery method, next-hop host, recipient) triple.

This feature is available in Postfix 2.0 and later.

sample_directory (default: /etc/postfix)
The name of the directory with example Postfix configuration files.

sender_based_routing (default: no)
This parameter should not be used. It was replaced by sender_dependent_relayhost_maps in Postfix ver-sion version
sion 2.3.

sender_bcc_maps (default: empty)
Optional BCC (blind carbon-copy) address lookup tables, indexed by sender address. The BCC address
(multiple results are not supported) is added when mail enters from outside of Postfix.

This feature is available in Postfix 2.1 and later.

The table search order is as follows:

Look up the "user+extension@domain.tld" address including the optional address extension.

Look up the "user@domain.tld" address without the optional address extension.

Look up the "user+extension" address local part when the sender domain equals $myorigin,
$mydestination, $inet_interfaces or $proxy_interfaces.

Look up the "user" address local part when the sender domain equals $myorigin, $mydestination,
$inet_interfaces or $proxy_interfaces.

Look up the "@domain.tld" part.

Specify the types and names of databases to use. After change, run "postmap /etc/post-fix/sender_bcc". /etc/postfix/sender_bcc".
fix/sender_bcc".

Note: if mail to the BCC address bounces it will be returned to the sender.

Example:

sender_bcc_maps = hash:/etc/postfix/sender_bcc

sender_canonical_classes (default: envelope_sender, header_sender)
What addresses are subject to sender_canonical_maps address mapping. By default, sender_canoni-cal_maps sender_canonical_maps
cal_maps address mapping is applied to envelope sender addresses, and to header sender addresses.

Specify one or more of: envelope_sender, header_sender

This feature is available in Postfix 2.2 and later.

sender_canonical_maps (default: empty)
Optional address mapping lookup tables for envelope and header sender addresses. The table format
and lookups are documented in canonical(5).

Example: you want to rewrite the SENDER address "user@ugly.domain" to "user@pretty.domain", while
still being able to send mail to the RECIPIENT address "user@ugly.domain".

Note: $sender_canonical_maps is processed before $canonical_maps.

Example:

sender_canonical_maps = hash:/etc/postfix/sender_canonical

sender_dependent_relayhost_maps (default: empty)
A sender-dependent override for the global relayhost parameter setting. The tables are searched by
the envelope sender address and @domain. This information is overruled with relay_transport,
default_transport and with the transport(5) table.

For safety reasons, this feature does not allow $number substitutions in regular expression maps.

This feature is available in Postfix 2.3 and later.

sendmail_path (default: see postconf -d output)
A Sendmail compatibility feature that specifies the location of the Postfix sendmail(1) command. This
command can be used to submit mail into the Postfix queue.

service_throttle_time (default: 60s)
How long the Postfix master(8) waits before forking a server that appears to be malfunctioning.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

setgid_group (default: postdrop)
The group ownership of set-gid Postfix commands and of group-writable Postfix directories. When this
parameter value is changed you need to re-run "postfix set-permissions" (with Postfix version 2.0 and
earlier: "/etc/postfix/post-install set-permissions".

show_user_unknown_table_name (default: yes)
Display the name of the recipient table in the "User unknown" responses. The extra detail makes
trouble shooting easier but also reveals information that is nobody elses business.

This feature is available in Postfix 2.0 and later.

showq_service_name (default: showq)
The name of the showq(8) service. This service produces mail queue status reports.

This feature is available in Postfix 2.0 and later.

smtp_always_send_ehlo (default: yes)
Always send EHLO at the start of an SMTP session.

With "smtp_always_send_ehlo = no", Postfix sends EHLO only when the word "ESMTP" appears in the
server greeting banner (example: 220 spike.porcupine.org ESMTP Postfix).

smtp_bind_address (default: empty)
An optional numerical network address that the Postfix SMTP client should bind to when making an IPv4
connection.

This can be specified in the main.cf file for all SMTP clients, or it can be specified in the mas-ter.cf master.cf
ter.cf file for a specific client, for example:

/etc/postfix/master.cf:
smtp ... smtp -o smtp_bind_address=11.22.33.44

Note 1: when inet_interfaces specifies no more than one IPv4 address, and that address is a non-loop-back non-loopback
back address, it is automatically used as the smtp_bind_address. This supports virtual IP hosting,
but can be a problem on multi-homed firewalls. See the inet_interfaces documentation for more detail.

Note 2: address information may be enclosed inside [], but this form is not required here.

smtp_bind_address6 (default: empty)
An optional numerical network address that the Postfix SMTP client should bind to when making an IPv6
connection.

This feature is available in Postfix 2.2 and later.

This can be specified in the main.cf file for all SMTP clients, or it can be specified in the mas-ter.cf master.cf
ter.cf file for a specific client, for example:

/etc/postfix/master.cf:
smtp ... smtp -o smtp_bind_address6=1:2:3:4:5:6:7:8

Note 1: when inet_interfaces specifies no more than one IPv6 address, and that address is a non-loop-back non-loopback
back address, it is automatically used as the smtp_bind_address6. This supports virtual IP hosting,
but can be a problem on multi-homed firewalls. See the inet_interfaces documentation for more detail.

Note 2: address information may be enclosed inside [], but this form is not recommended here.

smtp_cname_overrides_servername (default: version dependent)
Allow DNS CNAME records to override the servername that the Postfix SMTP client uses for logging,
SASL password lookup, TLS policy decisions, or TLS certificate verification. The value "no" hardens
Postfix smtp_tls_per_site hostname-based policies against false hostname information in DNS CNAME
records, and makes SASL password file lookups more predictable. This is the default setting as of
Postfix 2.3.

This feature is available in Postfix 2.2.9 and later.

smtp_connect_timeout (default: 30s)
The SMTP client time limit for completing a TCP connection, or zero (use the operating system built-in builtin
in time limit).

When no connection can be made within the deadline, the Postfix SMTP client tries the next address on
the mail exchanger list. Specify 0 to disable the time limit (i.e. use whatever timeout is imple-mented implemented
mented by the operating system).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

smtp_connection_cache_destinations (default: empty)
Permanently enable SMTP connection caching for the specified destinations. With SMTP connection
caching, a connection is not closed immediately after completion of a mail transaction. Instead, the
connection is kept open for up to $smtp_connection_cache_time_limit seconds. This allows connections
to be reused for other deliveries, and can improve mail delivery performance.

Specify a comma or white space separated list of destinations or pseudo-destinations:

if mail is sent without a relay host: a domain name (the right-hand side of an email address,
without the [] around a numeric IP address),

if mail is sent via a relay host: a relay host name (without [] or non-default TCP port), as
specified in main.cf or in the transport map,

if mail is sent via a UNIX-domain socket: a pathname (without the unix: prefix),

a /file/name with domain names and/or relay host names as defined above,

a "type:table" with domain names and/or relay hosts name on the left-hand side. The right-hand righthand
hand side result from "type:table" lookups is ignored.

This feature is available in Postfix 2.2 and later.

smtp_connection_cache_on_demand (default: yes)
Temporarily enable SMTP connection caching while a destination has a high volume of mail in the
active queue. With SMTP connection caching, a connection is not closed immediately after completion
of a mail transaction. Instead, the connection is kept open for up to $smtp_connec-tion_cache_time_limit $smtp_connection_cache_time_limit
tion_cache_time_limit seconds. This allows connections to be reused for other deliveries, and can
improve mail delivery performance.

This feature is available in Postfix 2.2 and later.

smtp_connection_cache_reuse_limit (default: 10)
When SMTP connection caching is enabled, the number of times that an SMTP session may be reused
before it is closed.

This feature is available in Postfix 2.2. In Postfix 2.3 it is replaced by $smtp_connection_re-use_time_limit. $smtp_connection_reuse_time_limit.
use_time_limit.

smtp_connection_cache_time_limit (default: 2s)
When SMTP connection caching is enabled, the amount of time that an unused SMTP client socket is kept
open before it is closed. Do not specify larger values without permission from the remote sites.

This feature is available in Postfix 2.2 and later.

smtp_connection_reuse_time_limit (default: 300s)
The amount of time during which Postfix will use an SMTP connection repeatedly. The timer starts
when the connection is initiated (i.e. it includes the connect, greeting and helo latency, in addi-tion addition
tion to the latencies of subsequent mail delivery transactions).

This feature addresses a performance stability problem with remote SMTP servers. This problem is not
specific to Postfix: it can happen when any MTA sends large amounts of SMTP email to a site that has
multiple MX hosts.

The problem starts when one of a set of MX hosts becomes slower than the rest. Even though SMTP
clients connect to fast and slow MX hosts with equal probability, the slow MX host ends up with more
simultaneous inbound connections than the faster MX hosts, because the slow MX host needs more time
to serve each client request.

The slow MX host becomes a connection attractor. If one MX host becomes N times slower than the
rest, it dominates mail delivery latency unless there are more than N fast MX hosts to counter the
effect. And if the number of MX hosts is smaller than N, the mail delivery latency becomes effec-tively effectively
tively that of the slowest MX host divided by the total number of MX hosts.

The solution uses connection caching in a way that differs from Postfix version 2.2. By limiting the
amount of time during which a connection can be used repeatedly (instead of limiting the number of
deliveries over that connection), Postfix not only restores fairness in the distribution of simulta-neous simultaneous
neous connections across a set of MX hosts, it also favors deliveries over connections that perform
well, which is exactly what we want.

The default reuse time limit, 300s, is comparable to the various smtp transaction timeouts which are
fair estimates of maximum excess latency for a slow delivery. Note that hosts may accept thousands
of messages over a single connection within the default connection reuse time limit. This number is
much larger than the default Postfix version 2.2 limit of 10 messages per cached connection. It may
prove necessary to lower the limit to avoid interoperability issues with MTAs that exhibit bugs when
many messages are delivered via a single connection. A lower reuse time limit risks losing the bene-fit benefit
fit of connection reuse when the average connection and mail delivery latency exceeds the reuse time
limit.

This feature is available in Postfix 2.3 and later.

smtp_data_done_timeout (default: 600s)
The SMTP client time limit for sending the SMTP ".", and for receiving the server response.

When no response is received within the deadline, a warning is logged that the mail may be delivered
multiple times.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

smtp_data_init_timeout (default: 120s)
The SMTP client time limit for sending the SMTP DATA command, and for receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

smtp_data_xfer_timeout (default: 180s)
The SMTP client time limit for sending the SMTP message content. When the connection makes no
progress for more than $smtp_data_xfer_timeout seconds the Postfix SMTP client terminates the trans-fer. transfer.
fer.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

smtp_defer_if_no_mx_address_found (default: no)
Defer mail delivery when no MX record resolves to an IP address.

The default (no) is to return the mail as undeliverable. With older Postfix versions the default was
to keep trying to deliver the mail until someone fixed the MX record or until the mail was too old.

Note: Postfix always ignores MX records with equal or worse preference than the local MTA itself.

This feature is available in Postfix 2.1 and later.

smtp_destination_concurrency_limit (default: $default_destination_concurrency_limit)
The maximal number of parallel deliveries to the same destination via the smtp message delivery
transport. This limit is enforced by the queue manager. The message delivery transport name is the
first field in the entry in the master.cf file.

smtp_destination_recipient_limit (default: $default_destination_recipient_limit)
The maximal number of recipients per delivery via the smtp message delivery transport. This limit is
enforced by the queue manager. The message delivery transport name is the first field in the entry in
the master.cf file.

Setting this parameter to a value of 1 changes the meaning of smtp_destination_concurrency_limit from
concurrency per domain into concurrency per recipient.

smtp_discard_ehlo_keyword_address_maps (default: empty)
Lookup tables, indexed by the remote SMTP server address, with case insensitive lists of EHLO key-words keywords
words (pipelining, starttls, auth, etc.) that the Postfix SMTP client will ignore in the EHLO
response from a remote SMTP server. See smtp_discard_ehlo_keywords for details. The table is not
indexed by hostname for consistency with smtpd_discard_ehlo_keyword_address_maps.

This feature is available in Postfix 2.2 and later.

smtp_discard_ehlo_keywords (default: empty)
A case insensitive list of EHLO keywords (pipelining, starttls, auth, etc.) that the Postfix SMTP
client will ignore in the EHLO response from a remote SMTP server.

This feature is available in Postfix 2.2 and later.

Notes:

Specify the silent-discard pseudo keyword to prevent this action from being logged.

Use the smtp_discard_ehlo_keyword_address_maps feature to discard EHLO keywords selectively.

smtp_enforce_tls (default: no)
Enforcement mode: require that remote SMTP servers use TLS encryption, and never send mail in the
clear. This also requires that the remote SMTP server hostname matches the information in the remote
server certificate, and that the remote SMTP server certificate was issued by a CA that is trusted by
the Postfix SMTP client. If the certificate doesn't verify or the hostname doesn't match, delivery is
deferred and mail stays in the queue.

The server hostname is matched against all names provided as dNSNames in the SubjectAlternativeName.
If no dNSNames are specified, the CommonName is checked. The behavior may be changed with the
smtp_tls_enforce_peername option.

This option is useful only if you are definitely sure that you will only connect to servers that sup-port support
port RFC 2487 _and_ that provide valid server certificates. Typical use is for clients that send all
their email to a dedicated mailhub.

This feature is available in Postfix 2.2 and later. With Postfix 2.3 and later use smtp_tls_secu-rity_level smtp_tls_security_level
rity_level instead.

smtp_fallback_relay (default: $fallback_relay)
Optional list of relay hosts for SMTP destinations that can't be found or that are unreachable. With
Postfix 2.2 and earlier this parameter is called fallback_relay.

By default, mail is returned to the sender when a destination is not found, and delivery is deferred
when a destination is unreachable.

To prevent mailer loops between MX hosts and fall-back hosts, Postfix version 2.3 and later will not
use the smtp_fallback_relay feature for destinations that it is MX host for.

smtp_generic_maps (default: empty)
Optional lookup tables that perform address rewriting in the SMTP client, typically to transform a
locally valid address into a globally valid address when sending mail across the Internet. This is
needed when the local machine does not have its own Internet domain name, but uses something like
localdomain.local instead.

The table format and lookups are documented in generic(5); examples are shown in the ADDRESS_REWRIT-ING_README ADDRESS_REWRITING_README
ING_README and STANDARD_CONFIGURATION_README documents.

This feature is available in Postfix 2.2 and later.

smtp_helo_name (default: $myhostname)
The hostname to send in the SMTP EHLO or HELO command.

The default value is the machine hostname. Specify a hostname or [ip.add.re.ss].

This information can be specified in the main.cf file for all SMTP clients, or it can be specified in
the master.cf file for a specific client, for example:

/etc/postfix/master.cf:
mysmtp ... smtp -o smtp_helo_name=foo.bar.com

This feature is available in Postfix 2.0 and later.

smtp_helo_timeout (default: 300s)
The SMTP client time limit for sending the HELO or EHLO command, and for receiving the initial server
response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

smtp_host_lookup (default: dns)
What mechanisms when the Postfix SMTP client uses to look up a host's IP address. This parameter is
ignored when DNS lookups are disabled.

Specify one of the following:

dns Hosts can be found in the DNS (preferred).

native Use the native naming service only (nsswitch.conf, or equivalent mechanism).

dns, native
Use the native service for hosts not found in the DNS.

This feature is available in Postfix 2.1 and later.

smtp_line_length_limit (default: 990)
The maximal length of message header and body lines that Postfix will send via SMTP. Longer lines
are broken by inserting "<CR><LF><SPACE>". This minimizes the damage to MIME formatted mail.

By default, the line length is limited to 990 characters, because some server implementations cannot
receive mail with long lines.

smtp_mail_timeout (default: 300s)
The SMTP client time limit for sending the MAIL FROM command, and for receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

smtp_mx_address_limit (default: 5)
The maximal number of MX (mail exchanger) IP addresses that can result from mail exchanger lookups,
or zero (no limit). Prior to Postfix version 2.3, this limit was disabled by default.

This feature is available in Postfix 2.1 and later.

smtp_mx_session_limit (default: 2)
The maximal number of SMTP sessions per delivery request before giving up or delivering to a fall-back fallback
back relay host, or zero (no limit). This restriction ignores sessions that fail to complete the SMTP
initial handshake (Postfix version 2.2 and earlier) or that fail to complete the EHLO and TLS hand-shake handshake
shake (Postfix version 2.3 and later).

This feature is available in Postfix 2.1 and later.

smtp_never_send_ehlo (default: no)
Never send EHLO at the start of an SMTP session. See also the smtp_always_send_ehlo parameter.

smtp_pix_workaround_delay_time (default: 10s)
How long the Postfix SMTP client pauses before sending ".<CR><LF>" in order to work around the PIX
firewall "<CR><LF>.<CR><LF>" bug.

Choosing a too short time makes this workaround ineffective when sending large messages over slow
network connections.

smtp_pix_workaround_maps (default: empty)
Lookup tables, indexed by the remote SMTP server address, with per-destination workarounds for CISCO
PIX firewall bugs. The table is not indexed by hostname for consistency with smtp_discard_ehlo_key-word_address_maps. smtp_discard_ehlo_keyword_address_maps.
word_address_maps.

This feature is available in Postfix 2.4 and later.

smtp_pix_workaround_threshold_time (default: 500s)
How long a message must be queued before the Postfix SMTP client turns on the PIX firewall
"<CR><LF>.<CR><LF>" bug workaround for delivery through firewalls with "smtp fixup" mode turned on.

By default, the workaround is turned off for mail that is queued for less than 500 seconds. In other
words, the workaround is normally turned off for the first delivery attempt.

Specify 0 to enable the PIX firewall "<CR><LF>.<CR><LF>" bug workaround upon the first delivery
attempt.

smtp_pix_workarounds (default: disable_esmtp, delay_dotcrlf)
A list that specifies zero or more workarounds for CISCO PIX firewall bugs. These workarounds are
implemented by the Postfix SMTP client. Workaround names are separated by comma or space, and are
case insensitive. This parameter setting can be overruled with per-destination smtp_pix_work-around_maps smtp_pix_workaround_maps
around_maps settings.

delay_dotcrlf
Insert a delay before sending ".<CR><LF>" after the end of the message content. The delay is
subject to the smtp_pix_workaround_delay_time and smtp_pix_workaround_threshold_time parameter
settings.

disable_esmtp
Disable all extended SMTP commands: send HELO instead of EHLO.

This feature is available in Postfix 2.4 and later. The default settings are backwards compatible
with earlier Postfix versions.

smtp_quit_timeout (default: 300s)
The SMTP client time limit for sending the QUIT command, and for receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

smtp_quote_rfc821_envelope (default: yes)
Quote addresses in SMTP MAIL FROM and RCPT TO commands as required by RFC 821. This includes putting
quotes around an address localpart that ends in ".".

The default is to comply with RFC 821. If you have to send mail to a broken SMTP server, configure a
special SMTP client in master.cf:

/etc/postfix/master.cf:
broken-smtp . . . smtp -o smtp_quote_rfc821_envelope=no

and route mail for the destination in question to the "broken-smtp" message delivery with a trans-port(5) transport(5)
port(5) table.

This feature is available in Postfix 2.1 and later.

smtp_randomize_addresses (default: yes)
Randomize the order of equal-preference MX host addresses. This is a performance feature of the
Postfix SMTP client.

smtp_rcpt_timeout (default: 300s)
The SMTP client time limit for sending the SMTP RCPT TO command, and for receiving the server
response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

smtp_rset_timeout (default: 20s)
The SMTP client time limit for sending the RSET command, and for receiving the server response. The
SMTP client sends RSET in order to finish a recipient address probe, or to verify that a cached ses-sion session
sion is still usable.

This feature is available in Postfix 2.1 and later.

smtp_sasl_auth_enable (default: no)
Enable SASL authentication in the Postfix SMTP client. By default, the Postfix SMTP client uses no
authentication.

Example:

smtp_sasl_auth_enable = yes

smtp_sasl_mechanism_filter (default: empty)
If non-empty, a Postfix SMTP client filter for the remote SMTP server's list of offered SASL mecha-nisms. mechanisms.
nisms. Different client and server implementations may support different mechanism lists. By
default, the Postfix SMTP client will use the intersection of the two. smtp_sasl_mechanism_filter
further restricts what server mechanisms the client will take into consideration.

Specify mechanism names, "/file/name" patterns or "type:table" lookup tables. The right-hand side
result from "type:table" lookups is ignored. Specify "!pattern" to exclude a mechanism name from the
list. The form "!/file/name" is supported only in Postfix version 2.4 and later.

This feature is available in Postfix 2.2 and later.

Examples:

smtp_sasl_mechanism_filter = plain, login
smtp_sasl_mechanism_filter = /etc/postfix/smtp_mechs
smtp_sasl_mechanism_filter = !gssapi, !login, static:rest

smtp_sasl_password_maps (default: empty)
Optional SMTP client lookup tables with one username:password entry per remote hostname or domain, or
sender address when sender-dependent authentication is enabled. If no username:password entry is
found, then the Postfix SMTP client will not attempt to authenticate to the remote host.

The Postfix SMTP client opens the lookup table before going to chroot jail, so you can leave the
password file in /etc/postfix.

smtp_sasl_path (default: empty)
Implementation-specific information that is passed through to the SASL plug-in implementation that is
selected with smtp_sasl_type. Typically this specifies the name of a configuration file or ren-dezvous rendezvous
dezvous point.

This feature is available in Postfix 2.3 and later.

smtp_sasl_security_options (default: noplaintext, noanonymous)
SASL security options; as of Postfix 2.3 the list of available features depends on the SASL client
implementation that is selected with smtp_sasl_type.

The following security features are defined for the cyrus client SASL implementation:

Specify zero or more of the following:

noplaintext
Disallow methods that use plaintext passwords.

noactive
Disallow methods subject to active (non-dictionary) attack.

nodictionary
Disallow methods subject to passive (dictionary) attack.

noanonymous
Disallow methods that allow anonymous authentication.

mutual_auth
Only allow methods that provide mutual authentication (not available with SASL version 1).

Example:

smtp_sasl_security_options = noplaintext

smtp_sasl_tls_security_options (default: $smtp_sasl_security_options)
The SASL authentication security options that the Postfix SMTP client uses for TLS encrypted SMTP
sessions.

This feature is available in Postfix 2.2 and later.

smtp_sasl_tls_verified_security_options (default: $smtp_sasl_tls_security_options)
The SASL authentication security options that the Postfix SMTP client uses for TLS encrypted SMTP
sessions with a verified server certificate. This feature is still under construction. It will not be
included in the Postfix 2.3 release.

This feature should be available in Postfix 2.4 and later.

smtp_sasl_type (default: cyrus)
The SASL plug-in type that the Postfix SMTP client should use for authentication. The available
types are listed with the "postconf -A" command.

This feature is available in Postfix 2.3 and later.

smtp_send_xforward_command (default: no)
Send the non-standard XFORWARD command when the Postfix SMTP server EHLO response announces XFORWARD
support.

This allows an "smtp" delivery agent, used for injecting mail into a content filter, to forward the
name, address, protocol and HELO name of the original client to the content filter and downstream
queuing SMTP server. This can produce more useful logging than localhost[127.0.0.1] etc.

This feature is available in Postfix 2.1 and later.

smtp_sender_dependent_authentication (default: no)
Enable sender-dependent authentication in the Postfix SMTP client; this is available only with SASL
authentication, and disables SMTP connection caching to ensure that mail from different senders will
use the appropriate credentials.

This feature is available in Postfix 2.3 and later.

smtp_skip_4xx_greeting (default: yes)
Skip SMTP servers that greet with a 4XX status code (go away, try again later).

By default, Postfix moves on the next mail exchanger. Specify "smtp_skip_4xx_greeting = no" if Post-fix Postfix
fix should defer delivery immediately.

This feature is available in Postfix 2.0 and earlier. Later Postfix versions always skip SMTP
servers that greet with a 4XX status code.

smtp_skip_5xx_greeting (default: yes)
Skip SMTP servers that greet with a 5XX status code (go away, do not try again later).

By default, the Postfix SMTP client moves on the next mail exchanger. Specify "smtp_skip_5xx_greeting
= no" if Postfix should bounce the mail immediately. The default setting is incorrect, but it is what
a lot of people expect to happen.

smtp_skip_quit_response (default: yes)
Do not wait for the response to the SMTP QUIT command.

smtp_starttls_timeout (default: 300s)
Time limit for Postfix SMTP client write and read operations during TLS startup and shutdown hand-shake handshake
shake procedures.

This feature is available in Postfix 2.2 and later.

smtp_tls_CAfile (default: empty)
The file with the certificate of the certification authority (CA) that issued the Postfix SMTP client
certificate. This is needed only when the CA certificate is not already present in the client cer-tificate certificate
tificate file.

Example:

smtp_tls_CAfile = /etc/postfix/CAcert.pem

This feature is available in Postfix 2.2 and later.

smtp_tls_CApath (default: empty)
Directory with PEM format certificate authority certificates that the Postfix SMTP client uses to
verify a remote SMTP server certificate. Don't forget to create the necessary "hash" links with, for
example, "$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs".

To use this option in chroot mode, this directory (or a copy) must be inside the chroot jail.

Example:

smtp_tls_CApath = /etc/postfix/certs

This feature is available in Postfix 2.2 and later.

smtp_tls_cert_file (default: empty)
File with the Postfix SMTP client RSA certificate in PEM format. This file may also contain the
Postfix SMTP client private RSA key, and these may be the same as the Postfix SMTP server RSA cer-tificate certificate
tificate and key file.

Do not configure client certificates unless you must present client TLS certificates to one or more
servers. Client certificates are not usually needed, and can cause problems in configurations that
work well without them. The recommended setting is to let the defaults stand:
smtp_tls_cert_file =
smtp_tls_dcert_file =
smtp_tls_key_file =
smtp_tls_dkey_file =

The best way to use the default settings is to comment out the above parameters in main.cf if
present.

In order to verify certificates, the CA certificate (in case of a certificate chain, all CA certifi-cates) certificates)
cates) must be available. You should add these certificates to the client certificate, the client
certificate first, then the issuing CA(s).

Example: the certificate for "client.dom.ain" was issued by "intermediate CA" which itself has a cer-tificate certificate
tificate of "root CA". Create the client.pem file with "cat client_cert.pem intermediate_CA.pem
root_CA.pem > client.pem".

If you also want to verify remote SMTP server certificates issued by these CAs, you can also add the
CA certificates to the smtp_tls_CAfile, in which case it is not necessary to have them in the
smtp_tls_cert_file or smtp_tls_dcert_file.

A certificate supplied here must be usable as an SSL client certificate and hence pass the "openssl
verify -purpose sslclient ..." test.

Example:

smtp_tls_cert_file = /etc/postfix/client.pem

This feature is available in Postfix 2.2 and later.

smtp_tls_cipherlist (default: empty)
Obsolete Postfix < 2.3 control for the Postfix SMTP client TLS cipher list. As this feature applies
to all TLS security levels, it is easy to create inter-operability problems by choosing a non-default
cipher list. Do not use a non-default TLS cipher list on hosts that deliver email to the public
Internet: you will be unable to send email to servers that only support the ciphers you exclude.
Using a restricted cipher list may be more appropriate for an internal MTA, where one can exert some
control over the TLS software and settings of the peer servers.

Note: do not use "" quotes around the parameter value.

This feature is available in Postfix version 2.2. It is not used with Postfix 2.3 and later; use
smtp_tls_mandatory_ciphers instead.

smtp_tls_dcert_file (default: empty)
File with the Postfix SMTP client DSA certificate in PEM format. This file may also contain the
Postfix SMTP client private DSA key.

See the discussion under smtp_tls_cert_file for more details.

Example:

smtp_tls_dcert_file = /etc/postfix/client-dsa.pem

This feature is available in Postfix 2.2 and later.

smtp_tls_dkey_file (default: $smtp_tls_dcert_file)
File with the Postfix SMTP client DSA private key in PEM format. This file may be combined with the
Postfix SMTP client DSA certificate file specified with $smtp_tls_dcert_file.

The private key must be accessible without a pass-phrase, i.e. it must not be encrypted, but file
permissions should grant read/write access only to the system superuser account ("root").

This feature is available in Postfix 2.2 and later.

smtp_tls_enforce_peername (default: yes)
With mandatory TLS encryption, require that the remote SMTP server hostname matches the information
in the remote SMTP server certificate. As of RFC 2487 the requirements for hostname checking for MTA
clients are not specified.

This option can be set to "no" to disable strict peer name checking. This setting has no effect on
sessions that are controlled via the smtp_tls_per_site table.

Disabling the hostname verification can make sense in closed environment where special CAs are cre-
ated. If not used carefully, this option opens the danger of a "man-in-the-middle" attack (the Com-monName CommonName
monName of this attacker will be logged).

This feature is available in Postfix 2.2 and later. With Postfix 2.3 and later use smtp_tls_secu-rity_level smtp_tls_security_level
rity_level instead.

smtp_tls_exclude_ciphers (default: empty)
List of ciphers or cipher types to exclude from the Postfix SMTP client cipher list at all TLS secu-rity security
rity levels. This is not an OpenSSL cipherlist, it is a simple list separated by whitespace and/or
commas. The elements are a single cipher, or one or more "+" separated cipher properties, in which
case only ciphers matching all the properties are excluded.

Examples (some of these will cause problems):

smtp_tls_exclude_ciphers = aNULL
smtp_tls_exclude_ciphers = MD5, DES
smtp_tls_exclude_ciphers = DES+MD5
smtp_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
smtp_tls_exclude_ciphers = kEDH+aRSA

The first setting, disables anonymous ciphers. The next setting disables ciphers that use the MD5
digest algorithm or the (single) DES encryption algorithm. The next setting disables ciphers that use
MD5 and DES together. The next setting disables the two ciphers "AES256-SHA" and "DES-CBC3-MD5". The
last setting disables ciphers that use "EDH" key exchange with RSA authentication.

This feature is available in Postfix 2.3 and later.

smtp_tls_key_file (default: $smtp_tls_cert_file)
File with the Postfix SMTP client RSA private key in PEM format. This file may be combined with the
Postfix SMTP client RSA certificate file specified with $smtp_tls_cert_file.

The private key must be accessible without a pass-phrase, i.e. it must not be encrypted, but file
permissions should grant read/write access only to the system superuser account ("root").

Example:

smtp_tls_key_file = $smtp_tls_cert_file

This feature is available in Postfix 2.2 and later.

smtp_tls_loglevel (default: 0)
Enable additional Postfix SMTP client logging of TLS activity. Each logging level also includes the
information that is logged at a lower logging level.

0 Disable logging of TLS activity.

1 Log TLS handshake and certificate information.

2 Log levels during TLS negotiation.

3 Log hexadecimal and ASCII dump of TLS negotiation process.

4 Log hexadecimal and ASCII dump of complete transmission after STARTTLS.

Use "smtp_tls_loglevel = 3" only in case of problems. Use of loglevel 4 is strongly discouraged.

This feature is available in Postfix 2.2 and later.

smtp_tls_mandatory_ciphers (default: medium)
The minimum TLS cipher grade that the Postfix SMTP client will use with mandatory TLS encryption.
The default value "medium" is suitable for most destinations with which you may want to enforce TLS,
and is beyond the reach of today's crypt-analytic methods. See smtp_tls_policy_maps for information
on how to configure ciphers on a per-destination basis.

The following cipher grades are supported:

export Enable the mainstream "EXPORT" grade or better OpenSSL ciphers. This is always used for
opportunistic encryption. It is not recommended for mandatory encryption unless you must
enforce TLS with "crippled" peers. The underlying cipherlist is specified via the
tls_export_cipherlist configuration parameter, which you are strongly encouraged to not
change. The default value of tls_export_cipherlist includes anonymous ciphers, but these are
automatically filtered out if the client is configured to verify server certificates. If you
must exclude anonymous ciphers also at the "encrypt" security level, set "smtp_tls_manda-tory_exclude_ciphers "smtp_tls_mandatory_exclude_ciphers
tory_exclude_ciphers = aNULL".

low Enable the mainstream "LOW" grade or better OpenSSL ciphers. This setting is only appropriate
for internal mail servers. The underlying cipherlist is specified via the tls_low_cipherlist
configuration parameter, which you are strongly encouraged to not change. The default value of
tls_low_cipherlist includes anonymous ciphers, but these are automatically filtered out if the
client is configured to verify server certificates. If you must exclude anonymous ciphers also
at the "encrypt" security level, set "smtp_tls_mandatory_exclude_ciphers = aNULL".

medium Enable the mainstream "MEDIUM" grade or better OpenSSL ciphers. The underlying cipherlist is
specified via the tls_medium_cipherlist configuration parameter, which you are strongly
encouraged to not change. The default value of tls_medium_cipherlist includes anonymous
ciphers, but these are automatically filtered out if the client is configured to verify server
certificates. If you must exclude anonymous ciphers also at the "encrypt" security level, set
"smtp_tls_mandatory_exclude_ciphers = aNULL".

high Enable only the mainstream "HIGH" grade OpenSSL ciphers. This setting is appropriate when all
mandatory TLS destinations support some of "HIGH" grade ciphers, this is not uncommon. The
underlying cipherlist is specified via the tls_high_cipherlist configuration parameter, which
you are strongly encouraged to not change. The default value of tls_high_cipherlist includes
anonymous ciphers, but these are automatically filtered out if the client is configured to
verify server certificates. If you must exclude anonymous ciphers also at the "encrypt" secu-rity security
rity level, set "smtp_tls_mandatory_exclude_ciphers = aNULL".

null Enable only the "NULL" OpenSSL ciphers, these provide authentication without encryption. This
setting is only appropriate in the rare case that all servers are prepared to use NULL ciphers
(not normally enabled in TLS servers). A plausible use-case is an LMTP server listening on a
UNIX-domain socket that is configured to support "NULL" ciphers. The underlying cipherlist is
specified via the tls_null_cipherlist configuration parameter, which you are strongly encour-aged encouraged
aged to not change. The default value of tls_null_cipherlist excludes anonymous ciphers
(OpenSSL 0.9.8 has NULL ciphers that offer data integrity without encryption or authentica-tion). authentication).
tion).

This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_exclude_ciphers (default: empty)
Additional list of ciphers or cipher types to exclude from the SMTP client cipher list at mandatory
TLS security levels. This list works in addition to the exclusions listed with
smtp_tls_exclude_ciphers (see there for syntax details).

This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_protocols (default: SSLv3, TLSv1)
List of TLS protocols that the Postfix SMTP client will use with mandatory TLS encryption. In
main.cf the values are separated by whitespace, commas or colons. In the policy table (see
smtp_tls_policy_maps) the only valid separator is colon. An empty value means allow all protocols.
The valid protocol names, (see \fBfBSSL_get_version(3)), are "SSLv2", "SSLv3" and "TLSv1".

Since SSL version 2 has known protocol weaknesses and is now deprecated, the default setting only
lists "SSLv3" and "TLSv1". This means that by default, SSL version 2 will not be used at the
"encrypt" security level and higher.

See the documentation of the smtp_tls_policy_maps parameter and TLS_README for more information about
security levels.

This feature is available in Postfix 2.3 and later.

smtp_tls_note_starttls_offer (default: no)
Log the hostname of a remote SMTP server that offers STARTTLS, when TLS is not already enabled for
that server.

The logfile record looks like:

postfix/smtp[pid]: Host offered STARTTLS: [name.of.host]

This feature is available in Postfix 2.2 and later.

smtp_tls_per_site (default: empty)
Optional lookup tables with the Postfix SMTP client TLS usage policy by next-hop destination and by
remote SMTP server hostname. When both lookups succeed, the more specific per-site policy (NONE,
MUST, etc) overrides the less specific one (MAY), and the more secure per-site policy (MUST, etc)
overrides the less secure one (NONE). With Postfix 2.3 and later smtp_tls_per_site is strongly dis-couraged: discouraged:
couraged: use smtp_tls_policy_maps instead.

Use of the bare hostname as the per-site table lookup key is discouraged. Always use the full desti-nation destination
nation nexthop (enclosed in [] with a possible ":port" suffix). A recipient domain or MX-enabled
transport next-hop with no port suffix may look like a bare hostname, but is still a suitable desti-nation. destination.
nation.

Specify a next-hop destination or server hostname on the left-hand side; no wildcards are allowed.
The next-hop destination is either the recipient domain, or the destination specified with a trans-port(5) transport(5)
port(5) table, the relayhost parameter, or the relay_transport parameter. On the right hand side
specify one of the following keywords:

NONE Don't use TLS at all. This overrides a less specific MAY lookup result from the alternate host
or next-hop lookup key, and overrides the global smtp_use_tls, smtp_enforce_tls, and
smtp_tls_enforce_peername settings.

MAY Try to use TLS if the server announces support, otherwise use the unencrypted connection. This
has less precedence than a more specific result (including NONE) from the alternate host or
next-hop lookup key, and has less precedence than the more specific global "smtp_enforce_tls =
yes" or "smtp_tls_enforce_peername = yes".

MUST_NOPEERMATCH
Require TLS encryption, but do not require that the remote SMTP server hostname matches the
information in the remote SMTP server certificate, or that the server certificate was issued
by a trusted CA. This overrides a less secure NONE or a less specific MAY lookup result from
the alternate host or next-hop lookup key, and overrides the global smtp_use_tls,
smtp_enforce_tls and smtp_tls_enforce_peername settings.

MUST Require TLS encryption, require that the remote SMTP server hostname matches the information
in the remote SMTP server certificate, and require that the remote SMTP server certificate was
issued by a trusted CA. This overrides a less secure NONE and MUST_NOPEERMATCH or a less spe-cific specific
cific MAY lookup result from the alternate host or next-hop lookup key, and overrides the
global smtp_use_tls, smtp_enforce_tls and smtp_tls_enforce_peername settings.

The above keywords correspond to the "none", "may", "encrypt" and "verify" security levels for the
new smtp_tls_security_level parameter introduced in Postfix 2.3. Starting with Postfix 2.3, and inde-pendently independently
pendently of how the policy is specified, the smtp_tls_mandatory_ciphers and smtp_tls_mandatory_pro-tocols smtp_tls_mandatory_protocols
tocols parameters only apply when TLS encryption is mandatory. Connections for which encryption is
optional enable all "export" grade and better ciphers.

As long as no secure DNS lookup mechanism is available, false hostnames in MX or CNAME responses can
change the server hostname that Postfix uses for TLS policy lookup and server certificate verifica-tion. verification.
tion. Even with a perfect match between the server hostname and the server certificate, there is no
guarantee that Postfix is connected to the right server. See TLS_README (Closing a DNS loophole with
obsolete per-site TLS policies) for a possible work-around.

This feature is available in Postfix 2.2 and later. With Postfix 2.3 and later use smtp_tls_pol-icy_maps smtp_tls_policy_maps
icy_maps instead.

smtp_tls_policy_maps (default: empty)
Optional lookup tables with the Postfix SMTP client TLS security policy by next-hop destination; when
a non-empty value is specified, this overrides the obsolete smtp_tls_per_site parameter. See
TLS_README for a more detailed discussion of TLS security levels.

The TLS policy table is indexed by the full next-hop destination, which is either the recipient
domain, or the verbatim next-hop specified in the transport table, $local_transport, $virtual_trans-port, $virtual_transport,
port, $relay_transport or $default_transport. This includes any enclosing square brackets and any
non-default destination server port suffix. The LMTP socket type prefix (inet: or unix:) is not
included in the lookup key.

Only the next-hop domain, or $myhostname with LMTP over UNIX-domain sockets, is used as the nexthop
name for certificate verification. The port and any enclosing square brackets are used in the table
lookup key, but are not used for server name verification.

When the lookup key is a domain name without enclosing square brackets or any :port suffix (typically
the recipient domain), and the full domain is not found in the table, just as with the transport(5)
table, the parent domain starting with a leading "." is matched recursively. This allows one to spec-ify specify
ify a security policy for a recipient domain and all its sub-domains.

The lookup result is a security level, followed by an optional list of whitespace and/or comma sepa-rated separated
rated name=value attributes that override related main.cf settings. The TLS security levels in order
of increasing security are:

none No TLS. No additional attributes are supported at this level.

may Opportunistic TLS. No additional attributes are supported at this level. Since sending in the
clear is acceptable, demanding stronger than default TLS security parameters merely reduces
inter-operability. Postfix 2.3 and later ignore the smtp_tls_mandatory_ciphers and
smtp_tls_mandatory_protocols parameters at this security level; all protocols are allowed and
"export" grade or better ciphers are used. When TLS handshakes fail, the connection is
retried with TLS disabled. This allows mail delivery to sites with non-interoperable TLS
implementations.

encrypt
Mandatory TLS encryption. At this level and higher the optional "ciphers" attribute overrides
the main.cf smtp_tls_mandatory_ciphers parameter and the optional "protocols" keyword over-rides overrides
rides the main.cf smtp_tls_mandatory_protocols parameter. In the policy table, multiple pro-tocols protocols
tocols must be separated by colons, as attribute values may not contain whitespace or commas.

verify Mandatory TLS verification. At this security level, DNS MX lookups are trusted to be secure
enough, and the name verified in the server certificate is usually obtained indirectly via
unauthenticated DNS MX lookups. The optional "match" attribute overrides the main.cf
smtp_tls_verify_cert_match parameter. In the policy table, multiple match patterns and strate-gies strategies
gies must be separated by colons. In practice explicit control over matching is more common
with the "secure" policy, described below.

secure Secure-channel TLS. At this security level, DNS MX lookups, though potentially used to deter-mine determine
mine the candidate next-hop gateway IP addresses, are not trusted to be secure enough for TLS
peername verification. Instead, the default name verified in the server certificate is
obtained directly from the next-hop, or is explicitly specified via the optional match
attribute which overrides the main.cf smtp_tls_secure_cert_match parameter. In the policy ta-ble, table,
ble, multiple match patterns and strategies must be separated by colons. The match attribute
is most useful when multiple domains are supported by common server, the policy entries for
additional domains specify matching rules for the primary domain certificate. While transport
table overrides routing the secondary domains to the primary nexthop also allow secure verifi-cation, verification,
cation, they risk delivery to the wrong destination when domains change hands or are re-assigned reassigned
assigned to new gateways. With the "match" attribute approach, routing is not perturbed, and
mail is deferred if verification of a new MX host fails.

Example:

main.cf:
smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
tls_policy:
example.edu none
example.mil may
example.gov encrypt protocols=TLSv1
example.com verify ciphers=high
example.net secure
.example.net secure match=.example.net:example.net
[mail.example.org]:587 secure match=nexthop

Note: The hostname strategy if listed in a non-default setting of smtp_tls_secure_cert_match or in
the match attribute in the policy table can render the secure level vulnerable to DNS forgery. Do not
use the hostname strategy for secure-channel configurations in environments where DNS security is not
assured.

This feature is available in Postfix 2.3 and later.

smtp_tls_scert_verifydepth (default: 5)
The verification depth for remote SMTP server certificates. A depth of 1 is sufficient, if the cer-tificate certificate
tificate is directly issued by a CA listed in the CA files. The default value (5) should suffice for
longer chains (the root CA issues special CA which then issues the actual certificate...).

This feature is available in Postfix 2.2 and later.

smtp_tls_secure_cert_match (default: nexthop, dot-nexthop)
The server certificate peername verification method for the "secure" TLS security level. In a
"secure" TLS policy table ($smtp_tls_policy_maps) entry the optional "match" attribute overrides this
main.cf setting.

This parameter specifies one or more patterns or strategies separated by commas, whitespace or
colons. In the policy table the only valid separator is the colon character.

For a description of the pattern and strategy syntax see the smtp_tls_verify_cert_match parameter.
The "hostname" strategy should be avoided in this context, as in the absence of a secure global DNS,
using the results of MX lookups in certificate verification is not immune to active (man-in-the-mid-dle) (man-in-the-middle)
dle) attacks on DNS.

Sample main.cf setting:

smtp_tls_secure_cert_match = nexthop

Sample policy table override:

example.net secure match=example.com:.example.com
\&.example.net secure match=example.com:.example.com

This feature is available in Postfix 2.3 and later.

smtp_tls_security_level (default: empty)
The default SMTP TLS security level for the Postfix SMTP client; when a non-empty value is specified,
this overrides the obsolete parameters smtp_use_tls, smtp_enforce_tls, and smtp_tls_enforce_peername.

Specify one of the following security levels:

none TLS will not be used unless enabled for specific destinations via smtp_tls_policy_maps.

may Opportunistic TLS. TLS will be used if supported by the server. Since sending in the clear is
acceptable, demanding stronger than default TLS security parameters merely reduces inter-oper-ability. inter-operability.
ability. Postfix 2.3 and later ignore the smtp_tls_mandatory_ciphers and smtp_tls_manda-tory_protocols smtp_tls_mandatory_protocols
tory_protocols parameters at this security level; all protocols are allowed and "export" grade
or better ciphers are used. When TLS handshakes fail, the connection is retried with TLS dis-abled. disabled.
abled. This allows mail delivery to sites with non-interoperable TLS implementations.

encrypt
Mandatory TLS encryption. Since a minimum level of security is intended, it reasonable to be
specific about sufficiently secure protocol versions and ciphers. At this security level and
higher, the main.cf parameters smtp_tls_mandatory_protocols and smtp_tls_mandatory_ciphers
specify the TLS protocols and minimum cipher grade which the administrator considers secure
enough for mandatory encrypted sessions. This security level is not an appropriate default for
systems delivering mail to the Internet.

verify Mandatory TLS verification. At this security level, DNS MX lookups are trusted to be secure
enough, and the name verified in the server certificate is usually obtained indirectly via
unauthenticated DNS MX lookups. The smtp_tls_verify_cert_match parameter controls how the
server name is verified. In practice explicit control over matching is more common at the
"secure" level, described below. This security level is not an appropriate default for systems
delivering mail to the Internet.

Examples:

No TLS, old-style: smtp_use_tls=no and smtp_enforce_tls=no.
main.cf:
smtp_tls_security_level = none

Opportunistic TLS:
main.cf:
smtp_tls_security_level = may

Mandatory (high-grade) TLS encryption:
main.cf:
smtp_tls_security_level = encrypt
smtp_tls_mandatory_ciphers = high

Mandatory TLS verification, of hostname or nexthop domain:
main.cf:
smtp_tls_security_level = verify
smtp_tls_mandatory_ciphers = high
smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

Secure channel TLS with exact nexthop name matching:
main.cf:
smtp_tls_security_level = secure
smtp_tls_mandatory_protocols = TLSv1
smtp_tls_mandatory_ciphers = high
smtp_tls_secure_cert_match = nexthop

This feature is available in Postfix 2.3 and later.

smtp_tls_session_cache_database (default: empty)
Name of the file containing the optional Postfix SMTP client TLS session cache. Specify a database
type that supports enumeration, such as btree or sdbm; there is no need to support concurrent access.
The file is created if it does not exist. The smtp(8) daemon does not use this parameter directly,
rather the cache is implemented indirectly in the tlsmgr(8) daemon. This means that per-smtp-instance
master.cf overrides of this parameter are not effective. Note, that each of the cache databases sup-ported supported
ported by tlsmgr(8) daemon: $smtpd_tls_session_cache_database, $smtp_tls_session_cache_database (and
with Postfix 2.3 and later $lmtp_session_cache_database), needs to be stored separately, it is not at
this time possible to store multiple caches in a single database.

Note: dbm databases are not suitable. TLS session objects are too large.

Example:

smtp_tls_session_cache_database = btree:/var/spool/postfix/smtp_scache

This feature is available in Postfix 2.2 and later.

smtp_tls_session_cache_timeout (default: 3600s)
The expiration time of Postfix SMTP client TLS session cache information. A cache cleanup is per-formed performed
formed periodically every $smtp_tls_session_cache_timeout seconds. As with $smtp_tls_ses-sion_cache_database, $smtp_tls_session_cache_database,
sion_cache_database, this parameter is implemented in the tlsmgr(8) daemon and therefore per-smtp-instance per-smtpinstance
instance master.cf overrides are not possible.

This feature is available in Postfix 2.2 and later.

smtp_tls_verify_cert_match (default: hostname)
The server certificate peername verification method for the "verify" TLS security level. In a "ver-ify" "verify"
ify" TLS policy table ($smtp_tls_policy_maps) entry the optional "match" attribute overrides this
main.cf setting.

This parameter specifies one or more patterns or strategies separated by commas, whitespace or
colons. In the policy table the only valid separator is the colon character.

Patterns specify domain names, or domain name suffixes:

example.com
Match the example.com domain, i.e. one of the names the server certificate must be exam-ple.com, example.com,
ple.com, upper and lower case distinctions are ignored.

.example.com
Match subdomains of the example.com domain, i.e. match a name in the server certificate that
consists of a non-zero number of labels followed by a .example.com suffix. Case distinctions
are ignored.

Strategies specify a transformation from the next-hop domain to the expected name in the server cer-tificate: certificate:
tificate:

nexthop
Match against the next-hop domain, which is either the recipient domain, or the transport
next-hop configured for the domain stripped of any optional socket type prefix, enclosing
square brackets and trailing port. When MX lookups are not suppressed, this is the original
nexthop domain prior to the MX lookup, not the result of the MX lookup. For LMTP delivery via
UNIX-domain sockets, the verified next-hop name is $myhostname. This strategy is suitable for
use with the "secure" policy. Case is ignored.

dot-nexthop
As above, but match server certificate names that are subdomains of the next-hop domain. Case
is ignored.

hostname
Match against the hostname of the server, often obtained via an unauthenticated DNS MX lookup.
For LMTP delivery via UNIX-domain sockets, the verified name is $myhostname. This matches the
verification strategy of the "MUST" keyword in the obsolete smtp_tls_per_site table, and is
suitable for use with the "verify" security level. When the next-hop name is enclosed in
square brackets to suppress MX lookups, the "hostname" strategy is the same as the "nexthop"
strategy. Case is ignored.

Sample main.cf setting:

smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

Sample policy table override:

example.com verify match=hostname:nexthop
\&.example.com verify match=example.com:.example.com:hostname

This feature is available in Postfix 2.3 and later.

smtp_use_tls (default: no)
Opportunistic mode: use TLS when a remote SMTP server announces STARTTLS support, otherwise send the
mail in the clear. Beware: some SMTP servers offer STARTTLS even if it is not configured. With Post-fix Postfix
fix < 2.3, if the TLS handshake fails, and no other server is available, delivery is deferred and
mail stays in the queue. If this is a concern for you, use the smtp_tls_per_site feature instead.

This feature is available in Postfix 2.2 and later. With Postfix 2.3 and later use smtp_tls_secu-
rity_level instead.

smtp_xforward_timeout (default: 300s)
The SMTP client time limit for sending the XFORWARD command, and for receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

This feature is available in Postfix 2.1 and later.

smtpd_authorized_verp_clients (default: $authorized_verp_clients)
What SMTP clients are allowed to specify the XVERP command. This command requests that mail be
delivered one recipient at a time with a per recipient return address.

By default, no clients are allowed to specify XVERP.

This parameter was renamed with Postfix version 2.1. The default value is backwards compatible with
Postfix version 2.0.

Note: IP version 6 address information must be specified inside [] in the smtpd_autho-rized_verp_clients smtpd_authorized_verp_clients
rized_verp_clients value, and in files specified with "/file/name". IP version 6 addresses contain
the ":" character, and would otherwise be confused with a "type:table" pattern.

smtpd_authorized_xclient_hosts (default: empty)
What SMTP clients are allowed to use the XCLIENT feature. This command overrides SMTP client infor-mation information
mation that is used for access control. Typical use is for SMTP-based content filters, fetchmail-like
programs, or SMTP server access rule testing. See the XCLIENT_README document for details.

This feature is available in Postfix 2.1 and later.

By default, no clients are allowed to specify XCLIENT.

Note: IP version 6 address information must be specified inside [] in the smtpd_autho-rized_xclient_hosts smtpd_authorized_xclient_hosts
rized_xclient_hosts value, and in files specified with "/file/name". IP version 6 addresses contain
the ":" character, and would otherwise be confused with a "type:table" pattern.

smtpd_authorized_xforward_hosts (default: empty)
What SMTP clients are allowed to use the XFORWARD feature. This command forwards information that is
used to improve logging after SMTP-based content filters. See the XFORWARD_README document for
details.

This feature is available in Postfix 2.1 and later.

By default, no clients are allowed to specify XFORWARD.

Note: IP version 6 address information must be specified inside [] in the smtpd_authorized_xfor-ward_hosts smtpd_authorized_xforward_hosts
ward_hosts value, and in files specified with "/file/name". IP version 6 addresses contain the ":"
character, and would otherwise be confused with a "type:table" pattern.

smtpd_banner (default: $myhostname ESMTP $mail_name)
The text that follows the 220 status code in the SMTP greeting banner. Some people like to see the
mail version advertised. By default, Postfix shows no version.

You MUST specify $myhostname at the start of the text. This is required by the SMTP protocol.

Example:

smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)

smtpd_client_connection_count_limit (default: 50)
How many simultaneous connections any client is allowed to make to this service. By default, the
limit is set to half the default process limit value.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must not be used to regulate legitimate
mail traffic.

This feature is available in Postfix 2.2 and later.

smtpd_client_connection_rate_limit (default: 0)
The maximal number of connection attempts any client is allowed to make to this service per time
unit. The time unit is specified with the anvil_rate_time_unit configuration parameter.

By default, a client can make as many connections per time unit as Postfix can accept.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must not be used to regulate legitimate
mail traffic.

This feature is available in Postfix 2.2 and later.

Example:

smtpd_client_connection_rate_limit = 1000

smtpd_client_event_limit_exceptions (default: $mynetworks)
Clients that are excluded from connection count, connection rate, or SMTP request rate restrictions.
See the mynetworks parameter description for the parameter value syntax.

By default, clients in trusted networks are excluded. Specify a list of network blocks, hostnames or
.domain names (the initial dot causes the domain to match any name below it).

Note: IP version 6 address information must be specified inside [] in the
smtpd_client_event_limit_exceptions value, and in files specified with "/file/name". IP version 6
addresses contain the ":" character, and would otherwise be confused with a "type:table" pattern.

This feature is available in Postfix 2.2 and later.

smtpd_client_message_rate_limit (default: 0)
The maximal number of message delivery requests that any client is allowed to make to this service
per time unit, regardless of whether or not Postfix actually accepts those messages. The time unit
is specified with the anvil_rate_time_unit configuration parameter.

By default, a client can send as many message delivery requests per time unit as Postfix can accept.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must not be used to regulate legitimate
mail traffic.

This feature is available in Postfix 2.2 and later.

Example:

smtpd_client_message_rate_limit = 1000

smtpd_client_new_tls_session_rate_limit (default: 0)
The maximal number of new (i.e., uncached) TLS sessions that a remote SMTP client is allowed to nego-tiate negotiate
tiate with this service per time unit. The time unit is specified with the anvil_rate_time_unit con-figuration configuration
figuration parameter.

By default, a remote SMTP client can negotiate as many new TLS sessions per time unit as Postfix can
accept.

To disable this feature, specify a limit of 0. Otherwise, specify a limit that is at least the per-client perclient
client concurrent session limit, or else legitimate client sessions may be rejected.

WARNING: The purpose of this feature is to limit abuse. It must not be used to regulate legitimate
mail traffic.

This feature is available in Postfix 2.3 and later.

Example:

smtpd_client_new_tls_session_rate_limit = 100

smtpd_client_recipient_rate_limit (default: 0)
The maximal number of recipient addresses that any client is allowed to send to this service per time
unit, regardless of whether or not Postfix actually accepts those recipients. The time unit is spec-ified specified
ified with the anvil_rate_time_unit configuration parameter.

By default, a client can make as many recipient addresses per time unit as Postfix can accept.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must not be used to regulate legitimate
mail traffic.

This feature is available in Postfix 2.2 and later.

Example:

smtpd_client_recipient_rate_limit = 1000

smtpd_client_restrictions (default: empty)
Optional SMTP server access restrictions in the context of a client SMTP connection request.

The default is to allow all connection requests.

Specify a list of restrictions, separated by commas and/or whitespace. Continue long lines by start-ing starting
ing the next line with whitespace. Restrictions are applied in the order as specified; the first
restriction that matches wins.

The following restrictions are specific to client hostname or client network address information.

check_ccert_access type:table
Use the client certificate fingerprint as lookup key for the specified access(5) database;
with Postfix version 2.2, also require that the SMTP client certificate is verified success-fully. successfully.
fully. This feature is available with Postfix version 2.2 and later.

check_client_access type:table
Search the specified access database for the client hostname, parent domains, client IP
address, or networks obtained by stripping least significant octets. See the access(5) manual
page for details.

permit_inet_interfaces
Permit the request when the client IP address matches $inet_interfaces.

permit_mynetworks
Permit the request when the client IP address matches any network or network address listed in
$mynetworks.

permit_sasl_authenticated
Permit the request when the client is successfully authenticated via the RFC 2554 (AUTH) pro-tocol. protocol.
tocol.

permit_tls_all_clientcerts
Permit the request when the remote SMTP client certificate is verified successfully. This
option must be used only if a special CA issues the certificates and only this CA is listed as
trusted CA, otherwise all clients with a recognized certificate would be allowed to relay.
This feature is available with Postfix version 2.2.

permit_tls_clientcerts
Permit the request when the remote SMTP client certificate is verified successfully, and the
certificate fingerprint is listed in $relay_clientcerts. This feature is available with Post-fix Postfix
fix version 2.2.

reject_rbl_client rbl_domain=d.d.d.d
Reject the request when the reversed client network address is listed with the A record
"d.d.d.d" under rbl_domain (Postfix version 2.1 and later only). If no "=d.d.d.d" is speci-fied, specified,
fied, reject the request when the reversed client network address is listed with any A record
under rbl_domain.
The maps_rbl_reject_code parameter specifies the response code for rejected requests (default:
554), the default_rbl_reply parameter specifies the default server reply, and the
rbl_reply_maps parameter specifies tables with server replies indexed by rbl_domain. This
feature is available in Postfix 2.0 and later.

reject_rhsbl_client rbl_domain=d.d.d.d
Reject the request when the client hostname is listed with the A record "d.d.d.d" under
rbl_domain (Postfix version 2.1 and later only). If no "=d.d.d.d" is specified, reject the
request when the client hostname is listed with any A record under rbl_domain. See the
reject_rbl_client description above for additional RBL related configuration parameters. This
feature is available in Postfix 2.0 and later.

reject_unknown_client_hostname (with Postfix < 2.3: reject_unknown_client)
Reject the request when 1) the client IP address->name mapping fails, 2) the name->address
mapping fails, or 3) the name->address mapping does not match the client IP address.
This is a stronger restriction than the reject_unknown_reverse_client_hostname feature, which
triggers only under condition 1) above.
The unknown_client_reject_code parameter specifies the response code for rejected requests
(default: 450). The reply is always 450 in case the address->name or name->address lookup
failed due to a temporary problem.

reject_unknown_reverse_client_hostname
Reject the request when the client IP address has no address->name mapping.
This is a weaker restriction than the reject_unknown_client_hostname feature, which requires
not only that the address->name and name->address mappings exist, but also that the two map-pings mappings
pings reproduce the client IP address.
The unknown_client_reject_code parameter specifies the response code for rejected requests
(default: 450). The reply is always 450 in case the address->name lookup failed due to a tem-porary temporary
porary problem.
This feature is available in Postfix 2.3 and later.

In addition, you can use any of the following generic restrictions. These restrictions are applica-ble applicable
ble in any SMTP command context.

check_policy_service servername
Query the specified policy server. See the SMTPD_POLICY_README document for details. This fea-ture feature
ture is available in Postfix 2.1 and later.

defer Defer the request. The client is told to try again later. This restriction is useful at the
end of a restriction list, to make the default policy explicit.
The defer_code parameter specifies the SMTP server reply code (default: 450).

defer_if_permit
Defer the request if some later restriction would result in an explicit or implicit PERMIT
action. This is useful when a blacklisting feature fails due to a temporary problem. This
feature is available in Postfix version 2.1 and later.

defer_if_reject
Defer the request if some later restriction would result in a REJECT action. This is useful
when a whitelisting feature fails due to a temporary problem. This feature is available in
Postfix version 2.1 and later.

permit Permit the request. This restriction is useful at the end of a restriction list, to make the
default policy explicit.

reject_multi_recipient_bounce
Reject the request when the envelope sender is the null address, and the message has multiple
envelope recipients. This usage has rare but legitimate applications: under certain condi-tions, conditions,
tions, multi-recipient mail that was posted with the DSN option NOTIFY=NEVER may be forwarded
with the null sender address.
Note: this restriction can only work reliably when used in smtpd_data_restrictions or
smtpd_end_of_data_restrictions, because the total number of recipients is not known at an ear-lier earlier
lier stage of the SMTP conversation. Use at the RCPT stage will only reject the second etc.
recipient.
The multi_recipient_bounce_reject_code parameter specifies the response code for rejected
requests (default: 550). This feature is available in Postfix 2.1 and later.

reject_plaintext_session
Reject the request when the connection is not encrypted. This restriction should not be used
before the client has had a chance to negotiate encryption with the AUTH or STARTTLS commands.
The plaintext_reject_code parameter specifies the response code for rejected requests
(default: 450). This feature is available in Postfix 2.3 and later.

reject_unauth_pipelining
Reject the request when the client sends SMTP commands ahead of time where it is not allowed,
or when the client sends SMTP commands ahead of time without knowing that Postfix actually
supports ESMTP command pipelining. This stops mail from bulk mail software that improperly
uses ESMTP command pipelining in order to speed up deliveries.
Note: reject_unauth_pipelining is not useful outside smtpd_data_restrictions when 1) the
client uses ESMTP (EHLO instead of HELO) and 2) with "smtpd_delay_reject = yes" (the default).
The use of reject_unauth_pipelining in the other restriction contexts is therefore not recom-mended. recommended.
mended.

reject Reject the request. This restriction is useful at the end of a restriction list, to make the
default policy explicit. The reject_code configuration parameter specifies the response code
to rejected requests (default: 554).

sleep seconds
Pause for the specified number of seconds and proceed with the next restriction in the list,
if any. This may stop zombie mail when used as:

/etc/postfix/main.cf:
smtpd_client_restrictions =
sleep 1, reject_unauth_pipelining
smtpd_delay_reject = no
This feature is available in Postfix 2.3.

warn_if_reject
Change the meaning of the next restriction, so that it logs a warning instead of rejecting a
request (look for logfile records that contain "reject_warning"). This is useful for testing
new restrictions in a "live" environment without risking unnecessary loss of mail.

Other restrictions that are valid in this context:

SMTP command specific restrictions that are described under the smtpd_helo_restrictions,
smtpd_sender_restrictions or smtpd_recipient_restrictions parameters. When helo, sender or
recipient restrictions are listed under smtpd_client_restrictions, they have effect only with
"smtpd_delay_reject = yes", so that $smtpd_client_restrictions is evaluated at the time of the
RCPT TO command.

Example:

smtpd_client_restrictions = permit_mynetworks, reject_unknown_client_hostname

smtpd_data_restrictions (default: empty)
Optional access restrictions that the Postfix SMTP server applies in the context of the SMTP DATA
command.

This feature is available in Postfix 2.0 and later.

The following restrictions are valid in this context:

Generic restrictions that can be used in any SMTP command context, described under
smtpd_client_restrictions.

SMTP command specific restrictions described under smtpd_client_restrictions,
smtpd_helo_restrictions, smtpd_sender_restrictions or smtpd_recipient_restrictions.

Examples:

smtpd_data_restrictions = reject_unauth_pipelining
smtpd_data_restrictions = reject_multi_recipient_bounce

smtpd_delay_open_until_valid_rcpt (default: yes)
Postpone the start of an SMTP mail transaction until a valid RCPT TO command is received. Specify
"no" to create a mail transaction as soon as the SMTP server receives a valid MAIL FROM command.

With sites that reject lots of mail, the default setting reduces the use of disk, CPU and memory
resources. The downside is that rejected recipients are logged with NOQUEUE instead of a mail trans-action transaction
action ID. This complicates the logfile analysis of multi-recipient mail.

This feature is available in Postfix 2.3 and later.

smtpd_delay_reject (default: yes)
Wait until the RCPT TO command before evaluating $smtpd_client_restrictions, $smtpd_helo_restrictions
and $smtpd_sender_restrictions, or wait until the ETRN command before evaluating
$smtpd_client_restrictions and $smtpd_helo_restrictions.

This feature is turned on by default because some clients apparently mis-behave when the Postfix SMTP
server rejects commands before RCPT TO.

The default setting has one major benefit: it allows Postfix to log recipient address information
when rejecting a client name/address or sender address, so that it is possible to find out whose mail
is being rejected.

smtpd_discard_ehlo_keyword_address_maps (default: empty)
Lookup tables, indexed by the remote SMTP client address, with case insensitive lists of EHLO key-words keywords
words (pipelining, starttls, auth, etc.) that the SMTP server will not send in the EHLO response to a
remote SMTP client. See smtpd_discard_ehlo_keywords for details. The table is not searched by host-name hostname
name for robustness reasons.

This feature is available in Postfix 2.2 and later.

smtpd_discard_ehlo_keywords (default: empty)
A case insensitive list of EHLO keywords (pipelining, starttls, auth, etc.) that the SMTP server will
not send in the EHLO response to a remote SMTP client.

This feature is available in Postfix 2.2 and later.

Notes:

Specify the silent-discard pseudo keyword to prevent this action from being logged.

Use the smtpd_discard_ehlo_keyword_address_maps feature to discard EHLO keywords selectively.

smtpd_end_of_data_restrictions (default: empty)
Optional access restrictions that the Postfix SMTP server applies in the context of the SMTP END-OF-DATA END-OFDATA
DATA command.

This feature is available in Postfix 2.2 and later.

See smtpd_data_restrictions for syntax details.

smtpd_enforce_tls (default: no)
Mandatory TLS: announce STARTTLS support to SMTP clients, and require that clients use TLS encryp-tion. encryption.
tion. According to RFC 2487 this MUST NOT be applied in case of a publicly-referenced SMTP server.
This option is off by default and should be used only on dedicated servers.

Note 1: "smtpd_enforce_tls = yes" implies "smtpd_tls_auth_only = yes".

Note 2: when invoked via "sendmail -bs", Postfix will never offer STARTTLS due to insufficient privi-leges privileges
leges to access the server private key. This is intended behavior.

This feature is available in Postfix 2.2 and later. With Postfix 2.3 and later use smtpd_tls_secu-rity_level smtpd_tls_security_level
rity_level instead.

smtpd_error_sleep_time (default: 1s)
With Postfix version 2.1 and later: the SMTP server response delay after a client has made more than
$smtpd_soft_error_limit errors, and fewer than $smtpd_hard_error_limit errors, without delivering
mail.

With Postfix version 2.0 and earlier: the SMTP server delay before sending a reject (4xx or 5xx)
response, when the client has made fewer than $smtpd_soft_error_limit errors without delivering mail.

smtpd_etrn_restrictions (default: empty)
Optional SMTP server access restrictions in the context of a client ETRN request.

The Postfix ETRN implementation accepts only destinations that are eligible for the Postfix "fast
flush" service. See the ETRN_README file for details.

The following restrictions are specific to the domain name information received with the ETRN com-mand. command.
mand.

check_etrn_access type:table
Search the specified access database for the ETRN domain name or its parent domains. See the
access(5) manual page for details.

Other restrictions that are valid in this context:

Generic restrictions that can be used in any SMTP command context, described under
smtpd_client_restrictions.

SMTP command specific restrictions described under smtpd_client_restrictions and
smtpd_helo_restrictions.

Example:

smtpd_etrn_restrictions = permit_mynetworks, reject

smtpd_expansion_filter (default: see postconf -d output)
What characters are allowed in $name expansions of RBL reply templates. Characters not in the allowed
set are replaced by "_". Use C like escapes to specify special characters such as whitespace.

This parameter is not subjected to $parameter expansion.

This feature is available in Postfix 2.0 and later.

smtpd_forbidden_commands (default: CONNECT, GET, POST)
List of commands that causes the Postfix SMTP server to immediately terminate the session with a 221
code. This can be used to disconnect clients that obviously attempt to abuse the system. In addition
to the commands listed in this parameter, commands that follow the "Label:" format of message headers
will also cause a disconnect.

This feature is available in Postfix 2.2 and later.

smtpd_hard_error_limit (default: 20)
The maximal number of errors a remote SMTP client is allowed to make without delivering mail. The
Postfix SMTP server disconnects when the limit is exceeded.

smtpd_helo_required (default: no)
Require that a remote SMTP client introduces itself at the beginning of an SMTP session with the HELO
or EHLO command.

Example:

smtpd_helo_required = yes

smtpd_helo_restrictions (default: empty)
Optional restrictions that the Postfix SMTP server applies in the context of the SMTP HELO command.

The default is to permit everything.

The following restrictions are specific to the hostname information received with the HELO or EHLO
command.

check_helo_access type:table
Search the specified access(5) database for the HELO or EHLO hostname or parent domains, and
execute the corresponding action.

check_helo_mx_access type:table
Search the specified access(5) database for the MX hosts for the HELO or EHLO hostname, and
execute the corresponding action. Note: a result of "OK" is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from blacklists. This feature is avail-able available
able in Postfix 2.1 and later.

check_helo_ns_access type:table
Search the specified access(5) database for the DNS servers for the HELO or EHLO hostname, and
execute the corresponding action. Note: a result of "OK" is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from blacklists. This feature is avail-able available
able in Postfix 2.1 and later.

reject_invalid_helo_hostname (with Postfix < 2.3: reject_invalid_hostname)
Reject the request when the HELO or EHLO hostname syntax is invalid.
The invalid_hostname_reject_code specifies the response code to rejected requests (default:
501).

reject_non_fqdn_helo_hostname (with Postfix < 2.3: reject_non_fqdn_hostname)
Reject the request when the HELO or EHLO hostname is not in fully-qualified domain form, as
required by the RFC.
The non_fqdn_reject_code parameter specifies the response code to rejected requests (default:
504).

reject_unknown_helo_hostname (with Postfix < 2.3: reject_unknown_hostname)
Reject the request when the HELO or EHLO hostname has no DNS A or MX record.
The unknown_hostname_reject_code specifies the response code to rejected requests (default:
450).

Other restrictions that are valid in this context:

Generic restrictions that can be used in any SMTP command context, described under
smtpd_client_restrictions.

Client hostname or network address specific restrictions described under smtpd_client_restric-
tions.

SMTP command specific restrictions described under smtpd_sender_restrictions or smtpd_recipi-ent_restrictions. smtpd_recipient_restrictions.
ent_restrictions. When sender or recipient restrictions are listed under smtpd_helo_restric-tions, smtpd_helo_restrictions,
tions, they have effect only with "smtpd_delay_reject = yes", so that $smtpd_helo_restrictions
is evaluated at the time of the RCPT TO command.

Examples:

smtpd_helo_restrictions = permit_mynetworks, reject_invalid_helo_hostname
smtpd_helo_restrictions = permit_mynetworks, reject_unknown_helo_hostname

smtpd_history_flush_threshold (default: 100)
The maximal number of lines in the Postfix SMTP server command history before it is flushed upon
receipt of EHLO, RSET, or end of DATA.

smtpd_junk_command_limit (default: 100)
The number of junk commands (NOOP, VRFY, ETRN or RSET) that a remote SMTP client can send before the
Postfix SMTP server starts to increment the error counter with each junk command. The junk command
count is reset after mail is delivered. See also the smtpd_error_sleep_time and
smtpd_soft_error_limit configuration parameters.

smtpd_milters (default: empty)
A list of Milter (mail filter) applications for new mail that arrives via the Postfix smtpd(8)
server. See the MILTER_README document for details.

This feature is available in Postfix 2.3 and later.

smtpd_noop_commands (default: empty)
List of commands that the Postfix SMTP server replies to with "250 Ok", without doing any syntax
checks and without changing state. This list overrides any commands built into the Postfix SMTP
server.

smtpd_null_access_lookup_key (default: <>)
The lookup key to be used in SMTP access(5) tables instead of the null sender address.

smtpd_peername_lookup (default: yes)
Attempt to look up the remote SMTP client hostname, and verify that the name matches the client IP
address. A client name is set to "unknown" when it cannot be looked up or verified, or when name
lookup is disabled. Turning off name lookup reduces delays due to DNS lookup and increases the maxi-mal maximal
mal inbound delivery rate.

This feature is available in Postfix 2.3 and later.

smtpd_policy_service_max_idle (default: 300s)
The time after which an idle SMTPD policy service connection is closed.

This feature is available in Postfix 2.1 and later.

smtpd_policy_service_max_ttl (default: 1000s)
The time after which an active SMTPD policy service connection is closed.

This feature is available in Postfix 2.1 and later.

smtpd_policy_service_timeout (default: 100s)
The time limit for connecting to, writing to or receiving from a delegated SMTPD policy server.

This feature is available in Postfix 2.1 and later.

smtpd_proxy_ehlo (default: $myhostname)
How the Postfix SMTP server announces itself to the proxy filter. By default, the Postfix hostname
is used.

This feature is available in Postfix 2.1 and later.

smtpd_proxy_filter (default: empty)
The hostname and TCP port of the mail filtering proxy server. The proxy receives all mail from the
Postfix SMTP server, and is supposed to give the result to another Postfix SMTP server process.

Specify "host:port" or "inet:host:port" for a TCP endpoint, or "unix:pathname" for a UNIX-domain end-point. endpoint.
point. The host can be specified as an IP address or as a symbolic name; no MX lookups are done.
When no "host" or "host:" are specified, the local machine is assumed. Pathname interpretation is
relative to the Postfix queue directory.

This feature is available in Postfix 2.1 and later.

The "inet:" and "unix:" prefixes are available in Postfix 2.3 and later.

smtpd_proxy_timeout (default: 100s)
The time limit for connecting to a proxy filter and for sending or receiving information. When a
connection fails the client gets a generic error message while more detailed information is logged to
the maillog file.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

This feature is available in Postfix 2.1 and later.

smtpd_recipient_limit (default: 1000)
The maximal number of recipients that the Postfix SMTP server accepts per message delivery request.

smtpd_recipient_overshoot_limit (default: 1000)
The number of recipients that a remote SMTP client can send in excess of the limit specified with
$smtpd_recipient_limit, before the Postfix SMTP server increments the per-session error count for
each excess recipient.

smtpd_recipient_restrictions (default: permit_mynetworks, reject_unauth_destination)
The access restrictions that the Postfix SMTP server applies in the context of the RCPT TO command.

By default, the Postfix SMTP server accepts:

Mail from clients whose IP address matches $mynetworks, or:

Mail to remote destinations that match $relay_domains, except for addresses that contain
sender-specified routing (user@elsewhere@domain), or:

Mail to local destinations that match $inet_interfaces or $proxy_interfaces, $mydestination,
$virtual_alias_domains, or $virtual_mailbox_domains.

IMPORTANT: If you change this parameter setting, you must specify at least one of the following
restrictions. Otherwise Postfix will refuse to receive mail:

reject, defer, defer_if_permit, reject_unauth_destination

The following restrictions are specific to the recipient address that is received with the RCPT TO
command.

check_recipient_access type:table
Search the specified access(5) database for the resolved RCPT TO address, domain, parent
domains, or localpart@, and execute the corresponding action.

check_recipient_mx_access type:table
Search the specified access(5) database for the MX hosts for the RCPT TO address, and execute
the corresponding action. Note: a result of "OK" is not allowed for safety reasons. Instead,
use DUNNO in order to exclude specific hosts from blacklists. This feature is available in
Postfix 2.1 and later.

check_recipient_ns_access type:table
Search the specified access(5) database for the DNS servers for the RCPT TO address, and exe-cute execute
cute the corresponding action. Note: a result of "OK" is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from blacklists. This feature is avail-able available
able in Postfix 2.1 and later.

permit_auth_destination
Permit the request when one of the following is true:

Postfix is mail forwarder: the resolved RCPT TO address matches $relay_domains or a subdomain
thereof, and the address contains no sender-specified routing (user@elsewhere@domain),

Postfix is the final destination: the resolved RCPT TO address matches $mydestination,
$inet_interfaces, $proxy_interfaces, $virtual_alias_domains, or $virtual_mailbox_domains, and
the address contains no sender-specified routing (user@elsewhere@domain).

permit_mx_backup
Permit the request when the local mail system is backup MX for the RCPT TO address, or when
the address is an authorized destination (see permit_auth_destination for definition).

Safety: permit_mx_backup does not accept addresses that have sender-specified routing informa-tion information
tion (example: user@elsewhere@domain).

Safety: permit_mx_backup can be vulnerable to mis-use when access is not restricted with per-mit_mx_backup_networks. permit_mx_backup_networks.
mit_mx_backup_networks.

Safety: as of Postfix version 2.3, permit_mx_backup no longer accepts the address when the
local mail system is primary MX for the recipient domain. Exception: permit_mx_backup accepts
the address when it specifies an authorized destination (see permit_auth_destination for defi-nition). definition).
nition).

Limitation: mail may be rejected in case of a temporary DNS lookup problem with Postfix prior
to version 2.0.

reject_non_fqdn_recipient
Reject the request when the RCPT TO address is not in fully-qualified domain form, as required
by the RFC.
The non_fqdn_reject_code parameter specifies the response code to rejected requests (default:
504).

reject_rhsbl_recipient rbl_domain=d.d.d.d
Reject the request when the RCPT TO domain is listed with the A record "d.d.d.d" under
rbl_domain (Postfix version 2.1 and later only). If no "=d.d.d.d" is specified, reject the
request when the RCPT TO domain is listed with any A record under rbl_domain.
The maps_rbl_reject_code parameter specifies the response code for rejected requests (default:
554); the default_rbl_reply parameter specifies the default server reply; and the
rbl_reply_maps parameter specifies tables with server replies indexed by rbl_domain. This
feature is available in Postfix version 2.0 and later.

reject_unauth_destination
Reject the request unless one of the following is true:

Postfix is mail forwarder: the resolved RCPT TO address matches $relay_domains or a subdomain
thereof, and contains no sender-specified routing (user@elsewhere@domain),

Postfix is the final destination: the resolved RCPT TO address matches $mydestination,
$inet_interfaces, $proxy_interfaces, $virtual_alias_domains, or $virtual_mailbox_domains, and
contains no sender-specified routing (user@elsewhere@domain).
The relay_domains_reject_code parameter specifies the response code for rejected requests
(default: 554).

reject_unknown_recipient_domain
Reject the request when Postfix is not final destination for the recipient address, and the
RCPT TO address has no DNS A or MX record, or when it has a malformed MX record such as a
record with a zero-length MX hostname (Postfix version 2.3 and later).
The unknown_address_reject_code parameter specifies the response code for rejected requests
(default: 450). The response is always 450 in case of a temporary DNS error.

reject_unlisted_recipient (with Postfix version 2.0: check_recipient_maps)
Reject the request when the RCPT TO address is not listed in the list of valid recipients for
its domain class. See the smtpd_reject_unlisted_recipient parameter description for details.
This feature is available in Postfix 2.1 and later.

reject_unverified_recipient
Reject the request when mail to the RCPT TO address is known to bounce, or when the recipient
address destination is not reachable. Address verification information is managed by the ver-ify(8) verify(8)
ify(8) server; see the ADDRESS_VERIFICATION_README file for details.
The unverified_recipient_reject_code parameter specifies the response when an address is known
to bounce (default: 450, change into 550 when you are confident that it is safe to do so).
Postfix replies with 450 when an address probe failed due to a temporary problem. This fea-ture feature
ture is available in Postfix 2.1 and later.

Other restrictions that are valid in this context:

Generic restrictions that can be used in any SMTP command context, described under
smtpd_client_restrictions.

SMTP command specific restrictions described under smtpd_client_restrictions,
smtpd_helo_restrictions and smtpd_sender_restrictions.

Example:

smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination

smtpd_reject_unlisted_recipient (default: yes)
Request that the Postfix SMTP server rejects mail for unknown recipient addresses, even when no
explicit reject_unlisted_recipient access restriction is specified. This prevents the Postfix queue
from filling up with undeliverable MAILER-DAEMON messages.

The recipient domain matches $mydestination, $inet_interfaces or $proxy_interfaces, but the
recipient is not listed in $local_recipient_maps, and $local_recipient_maps is not null.

The recipient domain matches $virtual_alias_domains but the recipient is not listed in $vir-tual_alias_maps. $virtual_alias_maps.
tual_alias_maps.

The recipient domain matches $virtual_mailbox_domains but the recipient is not listed in $vir-tual_mailbox_maps, $virtual_mailbox_maps,
tual_mailbox_maps, and $virtual_mailbox_maps is not null.

The recipient domain matches $relay_domains but the recipient is not listed in $relay_recipi-ent_maps, $relay_recipient_maps,
ent_maps, and $relay_recipient_maps is not null.

This feature is available in Postfix 2.1 and later.

smtpd_reject_unlisted_sender (default: no)
Request that the Postfix SMTP server rejects mail from unknown sender addresses, even when no
explicit reject_unlisted_sender access restriction is specified. This can slow down an explosion of
forged mail from worms or viruses.

The sender domain matches $mydestination, $inet_interfaces or $proxy_interfaces, but the
sender is not listed in $local_recipient_maps, and $local_recipient_maps is not null.

The sender domain matches $virtual_alias_domains but the sender is not listed in $vir-tual_alias_maps. $virtual_alias_maps.
tual_alias_maps.

The sender domain matches $virtual_mailbox_domains but the sender is not listed in $vir-tual_mailbox_maps, $virtual_mailbox_maps,
tual_mailbox_maps, and $virtual_mailbox_maps is not null.

The sender domain matches $relay_domains but the sender is not listed in $relay_recipi-ent_maps, $relay_recipient_maps,
ent_maps, and $relay_recipient_maps is not null.

This feature is available in Postfix 2.1 and later.

smtpd_restriction_classes (default: empty)
User-defined aliases for groups of access restrictions. The aliases can be specified in smtpd_recipi-ent_restrictions smtpd_recipient_restrictions
ent_restrictions etc., and on the right-hand side of a Postfix access(5) table.

One major application is for implementing per-recipient UCE control. See the RESTRIC-TION_CLASS_README RESTRICTION_CLASS_README
TION_CLASS_README document for other examples.

smtpd_sasl_application_name (default: smtpd)
The application name used for SASL server initialization. This controls the name of the SASL configu-ration configuration
ration file. The default value is smtpd, corresponding to a SASL configuration file named smtpd.conf.

This feature is available in Postfix 2.1 and 2.2. With Postfix 2.3 it was renamed to smtpd_sasl_path.

smtpd_sasl_auth_enable (default: no)
Enable SASL authentication in the Postfix SMTP server. By default, the Postfix SMTP server does not
use authentication.

If a remote SMTP client is authenticated, the permit_sasl_authenticated access restriction can be
used to permit relay access, like this:

smtpd_recipient_restrictions =
permit_mynetworks, permit_sasl_authenticated, ...

To reject all SMTP connections from unauthenticated clients, specify "smtpd_delay_reject = yes"
(which is the default) and use:

smtpd_client_restrictions = permit_sasl_authenticated, reject

See the SASL_README file for SASL configuration and operation details.

smtpd_sasl_authenticated_header (default: no)
Report the SASL authenticated user name in the smtpd(8) Received message header.

This feature is available in Postfix 2.3 and later.

smtpd_sasl_exceptions_networks (default: empty)
What SMTP clients Postfix will not offer AUTH support to.

Some clients (Netscape 4 at least) have a bug that causes them to require a login and password when-ever whenever
ever AUTH is offered, whether it's necessary or not. To work around this, specify, for example,
$mynetworks to prevent Postfix from offering AUTH to local clients.

Specify a list of network/netmask patterns, separated by commas and/or whitespace. The mask specifies
the number of bits in the network part of a host address. You can also "/file/name" or "type:table"
patterns. A "/file/name" pattern is replaced by its contents; a "type:table" lookup table is matched
when a table entry matches a lookup string (the lookup result is ignored). Continue long lines by
starting the next line with whitespace. Specify "!pattern" to exclude an address or network block
from the list. The form "!/file/name" is supported only in Postfix version 2.4 and later.

Note: IP version 6 address information must be specified inside [] in the smtpd_sasl_exceptions_net-works smtpd_sasl_exceptions_networks
works value, and in files specified with "/file/name". IP version 6 addresses contain the ":" char-acter, character,
acter, and would otherwise be confused with a "type:table" pattern.

Example:

smtpd_sasl_exceptions_networks = $mynetworks

This feature is available in Postfix 2.1 and later.

smtpd_sasl_local_domain (default: empty)
The name of the local SASL authentication realm.

By default, the local authentication realm name is the null string.

Examples:

smtpd_sasl_local_domain = $mydomain
smtpd_sasl_local_domain = $myhostname

smtpd_sasl_path (default: smtpd)
Implementation-specific information that is passed through to the SASL plug-in implementation that is
selected with smtpd_sasl_type. Typically this specifies the name of a configuration file or ren-dezvous rendezvous
dezvous point.

This feature is available in Postfix 2.3 and later. In earlier releases it was called
smtpd_sasl_application.

smtpd_sasl_security_options (default: noanonymous)
SASL security options; as of Postfix 2.3 the list of available features depends on the SASL server
implementation that is selected with smtpd_sasl_type.

The following security features are defined for the cyrus server SASL implementation:

Restrict what authentication mechanisms the Postfix SMTP server will offer to the client. The list
of available authentication mechanisms is system dependent.

Specify zero or more of the following:

noplaintext
Disallow methods that use plaintext passwords.

noactive
Disallow methods subject to active (non-dictionary) attack.

nodictionary
Disallow methods subject to passive (dictionary) attack.

noanonymous
Disallow methods that allow anonymous authentication.

mutual_auth
Only allow methods that provide mutual authentication (not available with SASL version 1).

By default, the Postfix SMTP server accepts plaintext passwords but not anonymous logins.

Warning: it appears that clients try authentication methods in the order as advertised by the server
(e.g., PLAIN ANONYMOUS CRAM-MD5) which means that if you disable plaintext passwords, clients will
log in anonymously, even when they should be able to use CRAM-MD5. So, if you disable plaintext
logins, disable anonymous logins too. Postfix treats anonymous login as no authentication.

Example:

smtpd_sasl_security_options = noanonymous, noplaintext

smtpd_sasl_tls_security_options (default: $smtpd_sasl_security_options)
The SASL authentication security options that the Postfix SMTP server uses for TLS encrypted SMTP
sessions.

This feature is available in Postfix 2.2 and later.

smtpd_sasl_type (default: cyrus)
The SASL plug-in type that the Postfix SMTP server should use for authentication. The available types
are listed with the "postconf -a" command.

This feature is available in Postfix 2.3 and later.

smtpd_sender_login_maps (default: empty)
Optional lookup table with the SASL login names that own sender (MAIL FROM) addresses.

Specify zero or more "type:table" lookup tables. With lookups from indexed files such as DB or DBM,
or from networked tables such as NIS, LDAP or SQL, the following search operations are done with a
sender address of user@domain:

1) user@domain
This table lookup is always done and has the highest precedence.

2) user
This table lookup is done only when the domain part of the sender address matches $myorigin,
$mydestination, $inet_interfaces or $proxy_interfaces.

3) @domain
This table lookup is done last and has the lowest precedence.

In all cases the result of table lookup must be either "not found" or a list of SASL login names sep-arated separated
arated by comma and/or whitespace.

smtpd_sender_restrictions (default: empty)
Optional restrictions that the Postfix SMTP server applies in the context of the MAIL FROM command.

The default is to permit everything.

The following restrictions are specific to the sender address received with the MAIL FROM command.

check_sender_access type:table
Search the specified access(5) database for the MAIL FROM address, domain, parent domains, or
localpart@, and execute the corresponding action.

check_sender_mx_access type:table
Search the specified access(5) database for the MX hosts for the MAIL FROM address, and exe-cute execute
cute the corresponding action. Note: a result of "OK" is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from blacklists. This feature is avail-able available
able in Postfix 2.1 and later.

check_sender_ns_access type:table
Search the specified access(5) database for the DNS servers for the MAIL FROM address, and
execute the corresponding action. Note: a result of "OK" is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from blacklists. This feature is avail-able available
able in Postfix 2.1 and later.

reject_authenticated_sender_login_mismatch
Enforces the reject_sender_login_mismatch restriction for authenticated clients only. This
feature is available in Postfix version 2.1 and later.

reject_non_fqdn_sender
Reject the request when the MAIL FROM address is not in fully-qualified domain form, as
required by the RFC.
The non_fqdn_reject_code parameter specifies the response code to rejected requests (default:
504).

reject_rhsbl_sender rbl_domain=d.d.d.d
Reject the request when the MAIL FROM domain is listed with the A record "d.d.d.d" under
rbl_domain (Postfix version 2.1 and later only). If no "=d.d.d.d" is specified, reject the
request when the MAIL FROM domain is listed with any A record under rbl_domain.
The maps_rbl_reject_code parameter specifies the response code for rejected requests (default:
554); the default_rbl_reply parameter specifies the default server reply; and the
rbl_reply_maps parameter specifies tables with server replies indexed by rbl_domain. This
feature is available in Postfix 2.0 and later.

reject_sender_login_mismatch
Reject the request when $smtpd_sender_login_maps specifies an owner for the MAIL FROM address,
but the client is not (SASL) logged in as that MAIL FROM address owner; or when the client is
(SASL) logged in, but the client login name doesn't own the MAIL FROM address according to
$smtpd_sender_login_maps.

reject_unauthenticated_sender_login_mismatch
Enforces the reject_sender_login_mismatch restriction for unauthenticated clients only. This
feature is available in Postfix version 2.1 and later.

reject_unknown_sender_domain
Reject the request when Postfix is not final destination for the sender address, and the MAIL
FROM address has no DNS A or MX record, or when it has a malformed MX record such as a record
with a zero-length MX hostname (Postfix version 2.3 and later).
The unknown_address_reject_code parameter specifies the response code for rejected requests
(default: 450). The response is always 450 in case of a temporary DNS error.

reject_unlisted_sender
Reject the request when the MAIL FROM address is not listed in the list of valid recipients
for its domain class. See the smtpd_reject_unlisted_sender parameter description for details.
This feature is available in Postfix 2.1 and later.

reject_unverified_sender
Reject the request when mail to the MAIL FROM address is known to bounce, or when the sender
address destination is not reachable. Address verification information is managed by the ver-ify(8) verify(8)
ify(8) server; see the ADDRESS_VERIFICATION_README file for details.
The unverified_sender_reject_code parameter specifies the response when an address is known to
bounce (default: 450, change into 550 when you are confident that it is safe to do so). Post-fix Postfix
fix replies with 450 when an address probe failed due to a temporary problem. This feature is
available in Postfix 2.1 and later.

Other restrictions that are valid in this context:

Generic restrictions that can be used in any SMTP command context, described under
smtpd_client_restrictions.

SMTP command specific restrictions described under smtpd_client_restrictions and
smtpd_helo_restrictions.

SMTP command specific restrictions described under smtpd_recipient_restrictions. When recipi-ent recipient
ent restrictions are listed under smtpd_sender_restrictions, they have effect only with
"smtpd_delay_reject = yes", so that $smtpd_sender_restrictions is evaluated at the time of the
RCPT TO command.

Examples:

smtpd_sender_restrictions = reject_unknown_sender_domain
smtpd_sender_restrictions = reject_unknown_sender_domain,
check_sender_access hash:/etc/postfix/access

smtpd_soft_error_limit (default: 10)
The number of errors a remote SMTP client is allowed to make without delivering mail before the Post-fix Postfix
fix SMTP server slows down all its responses.

With Postfix version 2.1 and later, the Postfix SMTP server delays all responses by
$smtpd_error_sleep_time seconds.

With Postfix versions 2.0 and earlier, the Postfix SMTP server delays all responses by (number
of errors) seconds.

smtpd_starttls_timeout (default: 300s)
The time limit for Postfix SMTP server write and read operations during TLS startup and shutdown
handshake procedures.

This feature is available in Postfix 2.2 and later.

smtpd_timeout (default: 300s)
The time limit for sending a Postfix SMTP server response and for receiving a remote SMTP client
request.

Note: if you set SMTP time limits to very large values you may have to update the global ipc_timeout
parameter.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

smtpd_tls_CAfile (default: empty)
The file with the certificate of the certification authority (CA) that issued the Postfix SMTP server
certificate. This is needed only when the CA certificate is not already present in the server cer-tificate certificate
tificate file. This file may also contain the CA certificates of other trusted CAs. You must use
this file for the list of trusted CAs if you want to use chroot-mode.

Example:

smtpd_tls_CAfile = /etc/postfix/CAcert.pem

This feature is available in Postfix 2.2 and later.

smtpd_tls_CApath (default: empty)
Directory with PEM format certificate authority certificates that the Postfix SMTP server offers to
remote SMTP clients for the purpose of client certificate verification. Do not forget to create the
necessary "hash" links with, for example, "$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs".

To use this option in chroot mode, this directory (or a copy) must be inside the chroot jail. Please
note that in this case the CA certificates are not offered to the client, so that e.g. Netscape
clients might not offer certificates issued by them. Use of this feature is therefore not recom-mended. recommended.
mended.

Example:

smtpd_tls_CApath = /etc/postfix/certs

This feature is available in Postfix 2.2 and later.

smtpd_tls_always_issue_session_ids (default: yes)
Force the Postfix SMTP server to issue a TLS session id, even when TLS session caching is turned off
(smtpd_tls_session_cache_database is empty). This behavior is compatible with Postfix < 2.3.

With Postfix 2.3 and later the Postfix SMTP server can disable session id generation when TLS session
caching is turned off. This keeps clients from caching sessions that almost certainly cannot be re-
used.

By default, the Postfix SMTP server always generates TLS session ids. This works around a known
defect in mail client applications such as MS Outlook, and may also prevent interoperability issues
with other MTAs.

Example:
smtpd_tls_always_issue_session_ids = no

This feature is available in Postfix 2.3 and later.

smtpd_tls_ask_ccert (default: no)
Ask a remote SMTP client for a client certificate. This information is needed for certificate based
mail relaying with, for example, the permit_tls_clientcerts feature.

Some clients such as Netscape will either complain if no certificate is available (for the list of
CAs in $smtpd_tls_CAfile) or will offer multiple client certificates to choose from. This may be
annoying, so this option is "off" by default.

This feature is available in Postfix 2.2 and later.

smtpd_tls_auth_only (default: no)
When TLS encryption is optional in the Postfix SMTP server, do not announce or accept SASL authenti-cation authentication
cation over unencrypted connections.

This feature is available in Postfix 2.2 and later.

smtpd_tls_ccert_verifydepth (default: 5)
The verification depth for remote SMTP client certificates. A depth of 1 is sufficient if the issuing
CA is listed in a local CA file. The default value should also suffice for longer chains (the root
CA issues special CA which then issues the actual certificate...).

This feature is available in Postfix 2.2 and later.

smtpd_tls_cert_file (default: empty)
File with the Postfix SMTP server RSA certificate in PEM format. This file may also contain the
Postfix SMTP server private RSA key.

Public Internet MX hosts without certificates signed by a "reputable" CA must generate, and be pre-pared prepared
pared to present to most clients, a self-signed or private-CA signed certificate. The client will not
be able to authenticate the server, but unless it is running Postfix 2.3 or similar software, it will
still insist on a server certificate.

For servers that are not public Internet MX hosts, Postfix 2.3 supports configurations with no cer-tificates. certificates.
tificates. This entails the use of just the anonymous TLS ciphers, which are not supported by typical
SMTP clients. Since such clients will not, as a rule, fall back to plain text after a TLS handshake
failure, the server will be unable to receive email from TLS enabled clients. To avoid accidental
configurations with no certificates, Postfix 2.3 enables certificate-less operation only when the
administrator explicitly sets "smtpd_tls_cert_file = none". This ensures that new Postfix configura-tions configurations
tions will not accidentally run with no certificates.

Both RSA and DSA certificates are supported. When both types are present, the cipher used determines
which certificate will be presented to the client. For Netscape and OpenSSL clients without special
cipher choices the RSA certificate is preferred.

In order to verify a certificate, the CA certificate (in case of a certificate chain, all CA certifi-cates) certificates)
cates) must be available. You should add these certificates to the server certificate, the server
certificate first, then the issuing CA(s).

Example: the certificate for "server.dom.ain" was issued by "intermediate CA" which itself has a cer-tificate certificate
tificate of "root CA". Create the server.pem file with "cat server_cert.pem intermediate_CA.pem
root_CA.pem > server.pem".

If you also want to verify client certificates issued by these CAs, you can add the CA certificates
to the smtpd_tls_CAfile, in which case it is not necessary to have them in the smtpd_tls_cert_file or
smtpd_tls_dcert_file.

A certificate supplied here must be usable as an SSL server certificate and hence pass the "openssl
verify -purpose sslserver ..." test.

Example:

smtpd_tls_cert_file = /etc/postfix/server.pem

This feature is available in Postfix 2.2 and later.

smtpd_tls_cipherlist (default: empty)
Obsolete Postfix < 2.3 control for the Postfix SMTP server TLS cipher list. It is easy to create
inter-operability problems by choosing a non-default cipher list. Do not use a non-default TLS
cipherlist for MX hosts on the public Internet. Clients that begin the TLS handshake, but are unable
to agree on a common cipher, may not be able to send any email to the SMTP server. Using a restricted
cipher list may be more appropriate for a dedicated MSA or an internal mailhub, where one can exert
some control over the TLS software and settings of the connecting clients.

Note: do not use "" quotes around the parameter value.

This feature is available with Postfix version 2.2. It is not used with Postfix 2.3 and later; use
smtpd_tls_mandatory_ciphers instead.

smtpd_tls_dcert_file (default: empty)
File with the Postfix SMTP server DSA certificate in PEM format. This file may also contain the
Postfix SMTP server private key.

See the discussion under smtpd_tls_cert_file for more details.

Example:

smtpd_tls_dcert_file = /etc/postfix/server-dsa.pem

This feature is available in Postfix 2.2 and later.

smtpd_tls_dh1024_param_file (default: empty)
File with DH parameters that the Postfix SMTP server should use with EDH ciphers.

Instead of using the exact same parameter sets as distributed with other TLS packages, it is more
secure to generate your own set of parameters with something like the following command:

openssl gendh -out /etc/postfix/dh_1024.pem -2 -rand /var/run/egd-pool 1024

Your actual source for entropy may differ. Some systems have /dev/random; on other system you may
consider using the "Entropy Gathering Daemon EGD", available at http://egd.sourceforge.net/

Example:

smtpd_tls_dh1024_param_file = /etc/postfix/dh_1024.pem

This feature is available with Postfix version 2.2.

smtpd_tls_dh512_param_file (default: empty)
File with DH parameters that the Postfix SMTP server should use with EDH ciphers.

See also the discussion under the smtpd_tls_dh1024_param_file configuration parameter.

Example:

smtpd_tls_dh512_param_file = /etc/postfix/dh_512.pem

This feature is available with Postfix version 2.2.

smtpd_tls_dkey_file (default: $smtpd_tls_dcert_file)
File with the Postfix SMTP server DSA private key in PEM format. This file may be combined with the
Postfix SMTP server DSA certificate file specified with $smtpd_tls_dcert_file.

The private key must be accessible without a pass-phrase, i.e. it must not be encrypted, but file
permissions should grant read/write access only to the system superuser account ("root").

This feature is available in Postfix 2.2 and later.

smtpd_tls_exclude_ciphers (default: empty)
List of ciphers or cipher types to exclude from the SMTP server cipher list at all TLS security lev-
els. Excluding valid ciphers can create interoperability problems. DO NOT exclude ciphers unless it
is essential to do so. This is not an OpenSSL cipherlist; it is a simple list separated by whitespace
and/or commas. The elements are a single cipher, or one or more "+" separated cipher properties, in
which case only ciphers matching all the properties are excluded.

Examples (some of these will cause problems):

smtpd_tls_exclude_ciphers = aNULL
smtpd_tls_exclude_ciphers = MD5, DES
smtpd_tls_exclude_ciphers = DES+MD5
smtpd_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
smtpd_tls_exclude_ciphers = kEDH+aRSA

The first setting disables anonymous ciphers. The next setting disables ciphers that use the MD5
digest algorithm or the (single) DES encryption algorithm. The next setting disables ciphers that use
MD5 and DES together. The next setting disables the two ciphers "AES256-SHA" and "DES-CBC3-MD5". The
last setting disables ciphers that use "EDH" key exchange with RSA authentication.

This feature is available in Postfix 2.3 and later.

smtpd_tls_key_file (default: $smtpd_tls_cert_file)
File with the Postfix SMTP server RSA private key in PEM format. This file may be combined with the
Postfix SMTP server certificate file specified with $smtpd_tls_cert_file.

The private key must be accessible without a pass-phrase, i.e. it must not be encrypted, but file
permissions should grant read/write access only to the system superuser account ("root").

smtpd_tls_loglevel (default: 0)
Enable additional Postfix SMTP server logging of TLS activity. Each logging level also includes the
information that is logged at a lower logging level.

0 Disable logging of TLS activity.

1 Log TLS handshake and certificate information.

2 Log levels during TLS negotiation.

3 Log hexadecimal and ASCII dump of TLS negotiation process.

4 Also log hexadecimal and ASCII dump of complete transmission after STARTTLS.

Use "smtpd_tls_loglevel = 3" only in case of problems. Use of loglevel 4 is strongly discouraged.

This feature is available in Postfix 2.2 and later.

smtpd_tls_mandatory_ciphers (default: medium)
The minimum TLS cipher grade that the Postfix SMTP server will use with mandatory TLS encryption.
Cipher types listed in smtpd_tls_mandatory_exclude_ciphers or smtpd_tls_exclude_ciphers are excluded
from the base definition of the selected cipher grade. With opportunistic TLS encryption, the
"export" grade is used unconditionally with exclusions specified only via smtpd_tls_exclude_ciphers.

The following cipher grades are supported:

export Enable the mainstream "EXPORT" grade or better OpenSSL ciphers. This is the most appropriate
setting for public MX hosts, and is always used with opportunistic TLS encryption. The under-
lying cipherlist is specified via the tls_export_cipherlist configuration parameter, which you
are strongly encouraged to not change. The default value of tls_export_cipherlist includes
anonymous ciphers, but these are automatically filtered out if the server is configured to ask
for client certificates. If you must always exclude anonymous ciphers, set
"smtpd_tls_exclude_ciphers = aNULL". To exclude anonymous ciphers only when TLS is enforced,
set "smtpd_tls_mandatory_exclude_ciphers = aNULL".

low Enable the mainstream "LOW" grade or better OpenSSL ciphers. The underlying cipherlist is
specified via the tls_low_cipherlist configuration parameter, which you are strongly encour-
aged to not change. The default value of tls_low_cipherlist includes anonymous ciphers, but
these are automatically filtered out if the server is configured to ask for client certifi-
cates. If you must always exclude anonymous ciphers, set "smtpd_tls_exclude_ciphers = aNULL".
To exclude anonymous ciphers only when TLS is enforced, set "smtpd_tls_manda-
tory_exclude_ciphers = aNULL".

medium Enable the mainstream "MEDIUM" grade or better OpenSSL ciphers. These are essentially the
128-bit or stronger ciphers. This is the default minimum strength for mandatory TLS encryp-
tion. MSAs that enforce TLS and have clients that do not support any "MEDIUM" or "HIGH" grade
ciphers, may need to configure a weaker ("low" or "export") minimum cipher grade. The underly-
ing cipherlist is specified via the tls_medium_cipherlist configuration parameter, which you
are strongly encouraged to not change. The default value of tls_medium_cipherlist includes
anonymous ciphers, but these are automatically filtered out if the server is configured to ask
for client certificates. If you must always exclude anonymous ciphers, set
"smtpd_tls_exclude_ciphers = aNULL". To exclude anonymous ciphers only when TLS is enforced,
set "smtpd_tls_mandatory_exclude_ciphers = aNULL".

high Enable only the mainstream "HIGH" grade OpenSSL ciphers. The underlying cipherlist is speci-
fied via the tls_high_cipherlist configuration parameter, which you are strongly encouraged to
not change. The default value of tls_high_cipherlist includes anonymous ciphers, but these are
automatically filtered out if the server is configured to ask for client certificates. If you
must always exclude anonymous ciphers, set "smtpd_tls_exclude_ciphers = aNULL". To exclude
anonymous ciphers only when TLS is enforced, set "smtpd_tls_mandatory_exclude_ciphers =
aNULL".

null Enable only the "NULL" OpenSSL ciphers, these provide authentication without encryption. This
setting is only appropriate in the rare case that all clients are prepared to use NULL ciphers
(not normally enabled in TLS clients). The underlying cipherlist is specified via the
tls_null_cipherlist configuration parameter, which you are strongly encouraged to not change.
The default value of tls_null_cipherlist excludes anonymous ciphers (OpenSSL 0.9.8 has NULL
ciphers that offer data integrity without encryption or authentication).

This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_exclude_ciphers (default: empty)
Additional list of ciphers or cipher types to exclude from the SMTP server cipher list at mandatory
TLS security levels. This list works in addition to the exclusions listed with
smtpd_tls_exclude_ciphers (see there for syntax details).

This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_protocols (default: SSLv3, TLSv1)
The TLS protocols accepted by the Postfix SMTP server with mandatory TLS encryption. With oppor-
tunistic TLS encryption, all protocols are always accepted. If the list is empty, the server supports
all available TLS protocol versions. A non-empty value is a list of protocol names separated by
whitespace, commas or colons. The supported protocol names are "SSLv2", "SSLv3" and "TLSv1", and are
not case sensitive.

Example:

smtpd_tls_mandatory_protocols = SSLv3, TLSv1

This feature is available in Postfix 2.3 and later.

smtpd_tls_received_header (default: no)
Request that the Postfix SMTP server produces Received: message headers that include information
about the protocol and cipher used, as well as the client CommonName and client certificate issuer
CommonName. This is disabled by default, as the information may be modified in transit through other
mail servers. Only information that was recorded by the final destination can be trusted.

This feature is available in Postfix 2.2 and later.

smtpd_tls_req_ccert (default: no)
With mandatory TLS encryption, require a remote SMTP client certificate in order to allow TLS connec-
tions to proceed. This option implies "smtpd_tls_ask_ccert = yes".

When TLS encryption is optional, this setting is ignored with a warning written to the mail log.

This feature is available in Postfix 2.2 and later.

smtpd_tls_security_level (default: empty)
The SMTP TLS security level for the Postfix SMTP server; when a non-empty value is specified, this
overrides the obsolete parameters smtpd_use_tls and smtpd_enforce_tls. This parameter is ignored with
"smtpd_tls_wrappermode = yes".

Specify one of the following security levels:

none TLS will not be used.

may Opportunistic TLS: announce STARTTLS support to SMTP clients, but do not require that clients
use TLS encryption.

encrypt
Mandatory TLS encryption: announce STARTTLS support to SMTP clients, and require that clients
use TLS encryption. According to RFC 2487 this MUST NOT be applied in case of a publicly-ref-
erenced SMTP server. Instead, this option should be used only on dedicated servers.

Note 1: the "verify" and "secure" levels are not supported. The Postfix SMTP server logs a warning
and uses "encrypt" instead. To verify SMTP client certificates, see TLS_README for a discussion of
the smtpd_tls_ask_ccert, smtpd_tls_req_ccert, and permit_tls_clientcerts features.

Note 2: The parameter setting "smtpd_tls_security_level = encrypt" implies "smtpd_tls_auth_only =
yes".

Note 3: when invoked via "sendmail -bs", Postfix will never offer STARTTLS due to insufficient privi-
leges to access the server private key. This is intended behavior.

This feature is available in Postfix 2.3 and later.

smtpd_tls_session_cache_database (default: empty)
Name of the file containing the optional Postfix SMTP server TLS session cache. Specify a database
type that supports enumeration, such as btree or sdbm; there is no need to support concurrent access.
The file is created if it does not exist. The smtpd(8) daemon does not use this parameter directly,
rather the cache is implemented indirectly in the tlsmgr(8) daemon. This means that per-smtpd-
instance master.cf overrides of this parameter are not effective. Note, that each of the cache data-
bases supported by tlsmgr(8) daemon: $smtpd_tls_session_cache_database, $smtp_tls_session_cache_data-
base (and with Postfix 2.3 and later $lmtp_session_cache_database), needs to be stored separately, it
is not at this time possible to store multiple caches in a single database.

Note: dbm databases are not suitable. TLS session objects are too large.

Example:

smtpd_tls_session_cache_database = btree:/var/spool/postfix/smtpd_scache

This feature is available in Postfix 2.2 and later.

smtpd_tls_session_cache_timeout (default: 3600s)
The expiration time of Postfix SMTP server TLS session cache information. A cache cleanup is per-
formed periodically every $smtpd_tls_session_cache_timeout seconds. As with $smtpd_tls_ses-
sion_cache_database, this parameter is implemented in the tlsmgr(8) daemon and therefore per-smtpd-
instance master.cf overrides are not possible.

This feature is available in Postfix 2.2 and later.

smtpd_tls_wrappermode (default: no)
Run the Postfix SMTP server in the non-standard "wrapper" mode, instead of using the STARTTLS com-
mand.

If you want to support this service, enable a special port in master.cf, and specify "-o
smtpd_tls_wrappermode=yes" on the SMTP server's command line. Port 465 (smtps) was once chosen for
this purpose.

This feature is available in Postfix 2.2 and later.

smtpd_use_tls (default: no)
Opportunistic TLS: announce STARTTLS support to SMTP clients, but do not require that clients use TLS
encryption.

Note: when invoked via "sendmail -bs", Postfix will never offer STARTTLS due to insufficient privi-
leges to access the server private key. This is intended behavior.

This feature is available in Postfix 2.2 and later. With Postfix 2.3 and later use smtpd_tls_secu-
rity_level instead.

soft_bounce (default: no)
Safety net to keep mail queued that would otherwise be returned to the sender. This parameter dis-
ables locally-generated bounces, and prevents the Postfix SMTP server from rejecting mail perma-
nently, by changing 5xx reply codes into 4xx. However, soft_bounce is no cure for address rewriting
mistakes or mail routing mistakes.

Example:

soft_bounce = yes

stale_lock_time (default: 500s)
The time after which a stale exclusive mailbox lockfile is removed. This is used for delivery to
file or mailbox.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

strict_7bit_headers (default: no)
Reject mail with 8-bit text in message headers. This blocks mail from poorly written applications.

This feature should not be enabled on a general purpose mail server, because it is likely to reject
legitimate email.

This feature is available in Postfix 2.0 and later.

strict_8bitmime (default: no)
Enable both strict_7bit_headers and strict_8bitmime_body.

This feature should not be enabled on a general purpose mail server, because it is likely to reject
legitimate email.

This feature is available in Postfix 2.0 and later.

strict_8bitmime_body (default: no)
Reject 8-bit message body text without 8-bit MIME content encoding information. This blocks mail
from poorly written applications.

Unfortunately, this also rejects majordomo approval requests when the included request contains valid
8-bit MIME mail, and it rejects bounces from mailers that do not MIME encapsulate 8-bit content (for
example, bounces from qmail or from old versions of Postfix).

This feature should not be enabled on a general purpose mail server, because it is likely to reject
legitimate email.

This feature is available in Postfix 2.0 and later.

strict_mime_encoding_domain (default: no)
Reject mail with invalid Content-Transfer-Encoding: information for the message/* or multipart/* MIME
content types. This blocks mail from poorly written software.

This feature should not be enabled on a general purpose mail server, because it will reject mail
after a single violation.

This feature is available in Postfix 2.0 and later.

strict_rfc821_envelopes (default: no)
Require that addresses received in SMTP MAIL FROM and RCPT TO commands are enclosed with <>, and that
those addresses do not contain RFC 822 style comments or phrases. This stops mail from poorly writ-
ten software.

By default, the Postfix SMTP server accepts RFC 822 syntax in MAIL FROM and RCPT TO addresses.

sun_mailtool_compatibility (default: no)
Obsolete SUN mailtool compatibility feature. Instead, use "mailbox_delivery_lock = dotlock".

swap_bangpath (default: yes)
Enable the rewriting of "site!user" into "user@site". This is necessary if your machine is connected
to UUCP networks. It is enabled by default.

Note: with Postfix version 2.2, message header address rewriting happens only when one of the follow-
ing conditions is true:

The message is received with the Postfix sendmail(1) command,

The message is received from a network client that matches $local_header_rewrite_clients,

The message is received from the network, and the remote_header_rewrite_domain parameter spec-
ifies a non-empty value.

To get the behavior before Postfix version 2.2, specify "local_header_rewrite_clients = static:all".

Example:

swap_bangpath = no

syslog_facility (default: mail)
The syslog facility of Postfix logging. Specify a facility as defined in syslog.conf(5). The default
facility is "mail".

Warning: a non-default syslog_facility setting takes effect only after a Postfix process has com-
pleted initialization. Errors during process initialization will be logged with the default facil-
ity. Examples are errors while parsing the command line arguments, and errors while accessing the
Postfix main.cf configuration file.

syslog_name (default: postfix)
The mail system name that is prepended to the process name in syslog records, so that "smtpd"
becomes, for example, "postfix/smtpd".

Warning: a non-default syslog_name setting takes effect only after a Postfix process has completed
initialization. Errors during process initialization will be logged with the default name. Examples
are errors while parsing the command line arguments, and errors while accessing the Postfix main.cf
configuration file.

tls_daemon_random_bytes (default: 32)
The number of pseudo-random bytes that an smtp(8) or smtpd(8) process requests from the tlsmgr(8)
server in order to seed its internal pseudo random number generator (PRNG). The default of 32 bytes
(equivalent to 256 bits) is sufficient to generate a 128bit (or 168bit) session key.

This feature is available in Postfix 2.2 and later.

tls_export_cipherlist (default: ALL:+RC4:@STRENGTH)
The OpenSSL cipherlist for "EXPORT" or higher grade ciphers. This defines the meaning of the "export"
setting in smtpd_tls_mandatory_ciphers, smtp_tls_mandatory_ciphers and lmtp_tls_mandatory_ciphers.
This is the cipherlist for the opportunistic ("may") TLS client security level and is the default
cipherlist for the SMTP server. You are strongly encouraged to not change this setting.

This feature is available in Postfix 2.3 and later.

tls_high_cipherlist (default: ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH)
The OpenSSL cipherlist for "HIGH" grade ciphers. This defines the meaning of the "high" setting in
smtpd_tls_mandatory_ciphers, smtp_tls_mandatory_ciphers and lmtp_tls_mandatory_ciphers. You are
strongly encouraged to not change this setting.

This feature is available in Postfix 2.3 and later.

tls_low_cipherlist (default: ALL:!EXPORT:+RC4:@STRENGTH)
The OpenSSL cipherlist for "LOW" or higher grade ciphers. This defines the meaning of the "low" set-
ting in smtpd_tls_mandatory_ciphers, smtp_tls_mandatory_ciphers and lmtp_tls_mandatory_ciphers. You
are strongly encouraged to not change this setting.

This feature is available in Postfix 2.3 and later.

tls_medium_cipherlist (default: ALL:!EXPORT:!LOW:+RC4:@STRENGTH)
The OpenSSL cipherlist for "MEDIUM" or higher grade ciphers. This defines the meaning of the "medium"
setting in smtpd_tls_mandatory_ciphers, smtp_tls_mandatory_ciphers and lmtp_tls_mandatory_ciphers.
This is the default cipherlist for mandatory TLS encryption in the TLS client (with anonymous ciphers
disabled when verifying server certificates). You are strongly encouraged to not change this setting.

This feature is available in Postfix 2.3 and later.

tls_null_cipherlist (default: eNULL:!aNULL)
The OpenSSL cipherlist for "NULL" grade ciphers that provide authentication without encryption. This
defines the meaning of the "null" setting in smtpd_mandatory_tls_ciphers, smtp_tls_mandatory_ciphers
and lmtp_tls_mandatory_ciphers. You are strongly encouraged to not change this setting.

This feature is available in Postfix 2.3 and later.

tls_random_bytes (default: 32)
The number of bytes that tlsmgr(8) reads from $tls_random_source when (re)seeding the in-memory
pseudo random number generator (PRNG) pool. The default of 32 bytes (256 bits) is good enough for
128bit symmetric keys. If using EGD or a device file, a maximum of 255 bytes is read.

This feature is available in Postfix 2.2 and later.

tls_random_exchange_name (default: ${config_directory}/prng_exch)
Name of the pseudo random number generator (PRNG) state file that is maintained by tlsmgr(8). The
file is created when it does not exist, and its length is fixed at 1024 bytes.

Since this file is modified by Postfix, it should probably be kept in the /var file system, instead
of under $config_directory. The location should not be inside the chroot jail.

This feature is available in Postfix 2.2 and later.

tls_random_prng_update_period (default: 3600s)
The time between attempts by tlsmgr(8) to save the state of the pseudo random number generator (PRNG)
to the file specified with $tls_random_exchange_name.

This feature is available in Postfix 2.2 and later.

tls_random_reseed_period (default: 3600s)
The maximal time between attempts by tlsmgr(8) to re-seed the in-memory pseudo random number genera-
tor (PRNG) pool from external sources. The actual time between re-seeding attempts is calculated
using the PRNG, and is between 0 and the time specified.

This feature is available in Postfix 2.2 and later.

tls_random_source (default: see postconf -d output)
The external entropy source for the in-memory tlsmgr(8) pseudo random number generator (PRNG) pool.
Be sure to specify a non-blocking source. If this source is not a regular file, the entropy source
type must be prepended: egd:/path/to/egd_socket for a source with EGD compatible socket interface,
or dev:/path/to/device for a device file.

Note: on OpenBSD systems specify /dev/arandom when /dev/urandom gives timeout errors.

This feature is available in Postfix 2.2 and later.

trace_service_name (default: trace)
The name of the trace service. This service is implemented by the bounce(8) daemon and maintains a
record of mail deliveries and produces a mail delivery report when verbose delivery is requested with
"sendmail -v".

This feature is available in Postfix 2.1 and later.

transport_maps (default: empty)
Optional lookup tables with mappings from recipient address to (message delivery transport, next-hop
destination). See transport(5) for details.

Specify zero or more "type:table" lookup tables. If you use this feature with local files, run
"postmap /etc/postfix/transport" after making a change.

For safety reasons, as of Postfix 2.3 this feature does not allow $number substitutions in regular
expression maps.

Examples:

transport_maps = dbm:/etc/postfix/transport
transport_maps = hash:/etc/postfix/transport

transport_retry_time (default: 60s)
The time between attempts by the Postfix queue manager to contact a malfunctioning message delivery
transport.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

trigger_timeout (default: 10s)
The time limit for sending a trigger to a Postfix daemon (for example, the pickup(8) or qmgr(8) dae-
mon). This time limit prevents programs from getting stuck when the mail system is under heavy load.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is s
(seconds).

undisclosed_recipients_header (default: To: undisclosed-recipients:;)
Message header that the Postfix cleanup(8) server inserts when a message contains no To: or Cc: mes-
sage header.

unknown_address_reject_code (default: 450)
The numerical Postfix SMTP server response code when a sender or recipient address is rejected by the
reject_unknown_sender_domain or reject_unknown_recipient_domain restriction. The response is always
450 in case of a temporary DNS error.

Do not change this unless you have a complete understanding of RFC 821.

unknown_client_reject_code (default: 450)
The numerical Postfix SMTP server response code when a client without valid address <=> name mapping
is rejected by the reject_unknown_client_hostname restriction. The SMTP server always replies with
450 when the mapping failed due to a temporary error condition.

Do not change this unless you have a complete understanding of RFC 821.

unknown_hostname_reject_code (default: 450)
The numerical Postfix SMTP server response code when the hostname specified with the HELO or EHLO
command is rejected by the reject_unknown_helo_hostname restriction.

Do not change this unless you have a complete understanding of RFC 821.

unknown_local_recipient_reject_code (default: 550)
The numerical Postfix SMTP server response code when a recipient address is local, and $local_recipi-
ent_maps specifies a list of lookup tables that does not match the recipient. A recipient address is
local when its domain matches $mydestination, $proxy_interfaces or $inet_interfaces.

The default setting is 550 (reject mail) but it is safer to initially use 450 (try again later) so
you have time to find out if your local_recipient_maps settings are OK.

Example:

unknown_local_recipient_reject_code = 450

This feature is available in Postfix 2.0 and later.

unknown_relay_recipient_reject_code (default: 550)
The numerical Postfix SMTP server reply code when a recipient address matches $relay_domains, and
relay_recipient_maps specifies a list of lookup tables that does not match the recipient address.

This feature is available in Postfix 2.0 and later.

unknown_virtual_alias_reject_code (default: 550)
The SMTP server reply code when a recipient address matches $virtual_alias_domains, and $vir-
tual_alias_maps specifies a list of lookup tables that does not match the recipient address.

This feature is available in Postfix 2.0 and later.

unknown_virtual_mailbox_reject_code (default: 550)
The SMTP server reply code when a recipient address matches $virtual_mailbox_domains, and $vir-
tual_mailbox_maps specifies a list of lookup tables that does not match the recipient address.

This feature is available in Postfix 2.0 and later.

unverified_recipient_reject_code (default: 450)
The numerical Postfix SMTP server response when a recipient address is rejected by the reject_unveri-
fied_recipient restriction.

Unlike elsewhere in Postfix, you can specify 250 in order to accept the address anyway.

Do not change this unless you have a complete understanding of RFC 821.

This feature is available in Postfix 2.1 and later.

unverified_sender_reject_code (default: 450)
The numerical Postfix SMTP server response code when a recipient address is rejected by the
reject_unverified_sender restriction.

Unlike elsewhere in Postfix, you can specify 250 in order to accept the address anyway.

Do not change this unless you have a complete understanding of RFC 821.

This feature is available in Postfix 2.1 and later.

verp_delimiter_filter (default: -=+)
The characters Postfix accepts as VERP delimiter characters on the Postfix sendmail(1) command line
and in SMTP commands.

This feature is available in Postfix 1.1 and later.

virtual_alias_domains (default: $virtual_alias_maps)
Postfix is final destination for the specified list of virtual alias domains, that is, domains for
which all addresses are aliased to addresses in other local or remote domains. The SMTP server vali-
dates recipient addresses with $virtual_alias_maps and rejects non-existent recipients. See also the
virtual alias domain class in the ADDRESS_CLASS_README file

This feature is available in Postfix 2.0 and later. The default value is backwards compatible with
Postfix version 1.1.

The default value is $virtual_alias_maps so that you can keep all information about virtual alias
domains in one place. If you have many users, it is better to separate information that changes more
frequently (virtual address -> local or remote address mapping) from information that changes less
frequently (the list of virtual domain names).

Specify a list of host or domain names, "/file/name" or "type:table" patterns, separated by commas
and/or whitespace. A "/file/name" pattern is replaced by its contents; a "type:table" lookup table is
matched when a table entry matches a lookup string (the lookup result is ignored). Continue long
lines by starting the next line with whitespace. Specify "!pattern" to exclude a host or domain name
from the list. The form "!/file/name" is supported only in Postfix version 2.4 and later.

See also the VIRTUAL_README and ADDRESS_CLASS_README documents for further information.

Example:

virtual_alias_domains = virtual1.tld virtual2.tld

virtual_alias_expansion_limit (default: 1000)
The maximal number of addresses that virtual alias expansion produces from each original recipient.

This feature is available in Postfix 2.1 and later.

virtual_alias_maps (default: $virtual_maps)
Optional lookup tables that alias specific mail addresses or domains to other local or remote
address. The table format and lookups are documented in virtual(5). For an overview of Postfix
address manipulations see the ADDRESS_REWRITING_README document.

This feature is available in Postfix 2.0 and later. The default value is backwards compatible with
Postfix version 1.1.

If you use this feature with indexed files, run "postmap /etc/postfix/virtual" after changing the
file.

Examples:

virtual_alias_maps = dbm:/etc/postfix/virtual
virtual_alias_maps = hash:/etc/postfix/virtual

virtual_alias_recursion_limit (default: 1000)
The maximal nesting depth of virtual alias expansion. Currently the recursion limit is applied only
to the left branch of the expansion graph, so the depth of the tree can in the worst case reach the
sum of the expansion and recursion limits. This may change in the future.

This feature is available in Postfix 2.1 and later.

virtual_destination_concurrency_limit (default: $default_destination_concurrency_limit)
The maximal number of parallel deliveries to the same destination via the virtual message delivery
transport. This limit is enforced by the queue manager. The message delivery transport name is the
first field in the entry in the master.cf file.

virtual_destination_recipient_limit (default: $default_destination_recipient_limit)
The maximal number of recipients per delivery via the virtual message delivery transport. This limit
is enforced by the queue manager. The message delivery transport name is the first field in the entry
in the master.cf file.

Setting this parameter to a value of 1 changes the meaning of virtual_destination_concurrency_limit
from concurrency per domain into concurrency per recipient.

virtual_gid_maps (default: empty)
Lookup tables with the per-recipient group ID for virtual(8) mailbox delivery.

In a lookup table, specify a left-hand side of "@domain.tld" to match any user in the specified
domain that does not have a specific "user@domain.tld" entry.

When a recipient address has an optional address extension (user+foo@domain.tld), the virtual(8)
delivery agent looks up the full address first, and when the lookup fails, it looks up the unextended
address (user@domain.tld).

Note 1: for security reasons, the virtual(8) delivery agent disallows regular expression substitution
of $1 etc. in regular expression lookup tables, because that would open a security hole.

Note 2: for security reasons, the virtual(8) delivery agent will silently ignore requests to use the
proxymap(8) server. Instead it will open the table directly. Before Postfix version 2.2, the vir-
tual(8) delivery agent will terminate with a fatal error.

virtual_mailbox_base (default: empty)
A prefix that the virtual(8) delivery agent prepends to all pathname results from $virtual_mail-
box_maps table lookups. This is a safety measure to ensure that an out of control map doesn't litter
the file system with mailboxes. While virtual_mailbox_base could be set to "/", this setting isn't
recommended.

Example:

virtual_mailbox_base = /var/mail

virtual_mailbox_domains (default: $virtual_mailbox_maps)
Postfix is final destination for the specified list of domains; mail is delivered via the $vir-
tual_transport mail delivery transport. By default this is the Postfix virtual(8) delivery agent.
The SMTP server validates recipient addresses with $virtual_mailbox_maps and rejects mail for non-
existent recipients. See also the virtual mailbox domain class in the ADDRESS_CLASS_README file.

This parameter expects the same syntax as the mydestination configuration parameter.

This feature is available in Postfix 2.0 and later. The default value is backwards compatible with
Postfix version 1.1.

virtual_mailbox_limit (default: 51200000)
The maximal size in bytes of an individual mailbox or maildir file, or zero (no limit).

virtual_mailbox_lock (default: see postconf -d output)
How to lock a UNIX-style virtual(8) mailbox before attempting delivery. For a list of available file
locking methods, use the "postconf -l" command.

This setting is ignored with maildir style delivery, because such deliveries are safe without appli-
cation-level locks.

Note 1: the dotlock method requires that the recipient UID or GID has write access to the parent
directory of the recipient's mailbox file.

Note 2: the default setting of this parameter is system dependent.

virtual_mailbox_maps (default: empty)
Optional lookup tables with all valid addresses in the domains that match $virtual_mailbox_domains.

In a lookup table, specify a left-hand side of "@domain.tld" to match any user in the specified
domain that does not have a specific "user@domain.tld" entry.

The virtual(8) delivery agent uses this table to look up the per-recipient mailbox or maildir path-
name. If the lookup result ends in a slash ("/"), maildir-style delivery is carried out, otherwise
the path is assumed to specify a UNIX-style mailbox file. Note that $virtual_mailbox_base is uncon-
ditionally prepended to this path.

Note 1: for security reasons, the virtual(8) delivery agent disallows regular expression substitution
of $1 etc. in regular expression lookup tables, because that would open a security hole.

virtual_maps (default: empty)
Optional lookup tables with a) names of domains for which all addresses are aliased to addresses in
other local or remote domains, and b) addresses that are aliased to addresses in other local or
remote domains. Available before Postfix version 2.0. With Postfix version 2.0 and later, this is
replaced by separate controls: virtual_alias_domains and virtual_alias_maps.

virtual_minimum_uid (default: 100)
The minimum user ID value that the virtual(8) delivery agent accepts as a result from $vir-
tual_uid_maps table lookup. Returned values less than this will be rejected, and the message will be
deferred.

virtual_transport (default: virtual)
The default mail delivery transport and next-hop destination for final delivery to domains listed
with $virtual_mailbox_domains. This information can be overruled with the transport(5) table.

Specify a string of the form transport:nexthop, where transport is the name of a mail delivery trans-
port defined in master.cf. The :nexthop part is optional. For more details see the transport(5)
manual page.

This feature is available in Postfix 2.0 and later.

virtual_uid_maps (default: empty)
Lookup tables with the per-recipient user ID that the virtual(8) delivery agent uses while writing to
the recipient's mailbox.

In a lookup table, specify a left-hand side of "@domain.tld" to match any user in the specified
domain that does not have a specific "user@domain.tld" entry.

Note 1: for security reasons, the virtual(8) delivery agent disallows regular expression substitution
of $1 etc. in regular expression lookup tables, because that would open a security hole.

SEE ALSO
postconf(1), Postfix configuration parameter maintenance
master(5), Postfix daemon configuration maintenance

LICENSE
The Secure Mailer license must be distributed with this software.

AUTHOR(S)
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA

POSTCONF(5)

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