VIRTUAL(8) VIRTUAL(8)
NAME
virtual - Postfix virtual domain mail delivery agent
SYNOPSIS
virtual [generic Postfix daemon options]
DESCRIPTION
The virtual(8) delivery agent is designed for virtual mail hosting services. Originally based on the
Postfix local(8) delivery agent, this agent looks up recipients with map lookups of their full recip-ient recipient
ient address, instead of using hard-coded unix password file lookups of the address local part only.
This delivery agent only delivers mail. Other features such as mail forwarding, out-of-office noti-fications, notifications,
fications, etc., must be configured via virtual_alias maps or via similar lookup mechanisms.
MAILBOX LOCATION
The mailbox location is controlled by the virtual_mailbox_base and virtual_mailbox_maps configuration
parameters (see below). The virtual_mailbox_maps table is indexed by the recipient address as
described under TABLE SEARCH ORDER below.
The mailbox pathname is constructed as follows:
$virtual_mailbox_base/$virtual_mailbox_maps(recipient)
where recipient is the full recipient address.
UNIX MAILBOX FORMAT
When the mailbox location does not end in /, the message is delivered in UNIX mailbox format. This
format stores multiple messages in one textfile.
The virtual(8) delivery agent prepends a "From sender time_stamp" envelope header to each message,
prepends a Delivered-To: message header with the envelope recipient address, prepends an X-Original-To: X-OriginalTo:
To: header with the recipient address as given to Postfix, prepends a Return-Path: message header
with the envelope sender address, prepends a > character to lines beginning with "From ", and appends
an empty line.
The mailbox is locked for exclusive access while delivery is in progress. In case of problems, an
attempt is made to truncate the mailbox to its original length.
QMAIL MAILDIR FORMAT
When the mailbox location ends in /, the message is delivered in qmail maildir format. This format
stores one message per file.
The virtual(8) delivery agent prepends a Delivered-To: message header with the final envelope recipi-ent recipient
ent address, prepends an X-Original-To: header with the recipient address as given to Postfix, and
prepends a Return-Path: message header with the envelope sender address.
By definition, maildir format does not require application-level file locking during mail delivery or
retrieval.
MAILBOX OWNERSHIP
Mailbox ownership is controlled by the virtual_uid_maps and virtual_gid_maps lookup tables, which are
indexed with the full recipient address. Each table provides a string with the numerical user and
group ID, respectively.
The virtual_minimum_uid parameter imposes a lower bound on numerical user ID values that may be spec-ified specified
ified in any virtual_uid_maps.
CASE FOLDING
All delivery decisions are made using the full recipient address, folded to lower case. See also the
next section for a few exceptions with optional address extensions.
TABLE SEARCH ORDER
Normally, a lookup table is specified as a text file that serves as input to the postmap(1) command.
The result, an indexed file in dbm or db format, is used for fast searching by the mail system.
The search order is as follows. The search stops upon the first successful lookup.
When the recipient has an optional address extension the user+extension@domain.tld address is
looked up first.
With Postfix versions before 2.1, the optional address extension is always ignored.
The user@domain.tld address, without address extension, is looked up next.
Finally, the recipient @domain is looked up.
When the table is provided via other means such as NIS, LDAP or SQL, the same lookups are done as for
ordinary indexed files.
Alternatively, a table can be provided as a regular-expression map where patterns are given as regu-lar regular
lar expressions. In that case, only the full recipient address is given to the regular-expression
map.
SECURITY
The virtual(8) delivery agent is not security sensitive, provided that the lookup tables with recipi-ent recipient
ent user/group ID information are adequately protected. This program is not designed to run chrooted.
The virtual(8) delivery agent disallows regular expression substitution of $1 etc. in regular expres-sion expression
sion lookup tables, because that would open a security hole.
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 virtual delivery agent will terminate
with a fatal error.
STANDARDS
RFC 822 (ARPA Internet Text Messages)
DIAGNOSTICS
Mail bounces when the recipient has no mailbox or when the recipient is over disk quota. In all other
cases, mail for an existing recipient is deferred and a warning is logged.
Problems and transactions are logged to syslogd(8). Corrupted message files are marked so that the
queue manager can move them to the corrupt queue afterwards.
Depending on the setting of the notify_classes parameter, the postmaster is notified of bounces and
of other trouble.
BUGS
This delivery agent supports address extensions in email addresses and in lookup table keys, but does
not propagate address extension information to the result of table lookup.
Postfix should have lookup tables that can return multiple result attributes. In order to avoid the
inconvenience of maintaining three tables, use an LDAP or MYSQL database.
CONFIGURATION PARAMETERS
Changes to main.cf are picked up automatically, as virtual(8) processes run for only a limited amount
of time. Use the command "postfix reload" to speed up a change.
The text below provides only a parameter summary. See postconf(5) for more details including exam-ples. examples.
ples.
MAILBOX DELIVERY CONTROLS
virtual_mailbox_base (empty)
A prefix that the virtual(8) delivery agent prepends to all pathname results from $vir-tual_mailbox_maps $virtual_mailbox_maps
tual_mailbox_maps table lookups.
virtual_mailbox_maps (empty)
Optional lookup tables with all valid addresses in the domains that match $virtual_mail-box_domains. $virtual_mailbox_domains.
box_domains.
virtual_minimum_uid (100)
The minimum user ID value that the virtual(8) delivery agent accepts as a result from $vir-tual_uid_maps $virtual_uid_maps
tual_uid_maps table lookup.
virtual_uid_maps (empty)
Lookup tables with the per-recipient user ID that the virtual(8) delivery agent uses while
writing to the recipient's mailbox.
virtual_gid_maps (empty)
Lookup tables with the per-recipient group ID for virtual(8) mailbox delivery.
Available in Postfix version 2.0 and later:
virtual_mailbox_domains ($virtual_mailbox_maps)
Postfix is final destination for the specified list of domains; mail is delivered via the
$virtual_transport mail delivery transport.
virtual_transport (virtual)
The default mail delivery transport and next-hop destination for final delivery to domains
listed with $virtual_mailbox_domains.
LOCKING CONTROLS
virtual_mailbox_lock (see 'postconf -d' output)
How to lock a UNIX-style virtual(8) mailbox before attempting delivery.
deliver_lock_attempts (20)
The maximal number of attempts to acquire an exclusive lock on a mailbox file or bounce(8)
logfile.
deliver_lock_delay (1s)
The time between attempts to acquire an exclusive lock on a mailbox file or bounce(8) logfile.
stale_lock_time (500s)
The time after which a stale exclusive mailbox lockfile is removed.
RESOURCE AND RATE CONTROLS
virtual_destination_concurrency_limit ($default_destination_concurrency_limit)
The maximal number of parallel deliveries to the same destination via the virtual message
delivery transport.
virtual_destination_recipient_limit ($default_destination_recipient_limit)
The maximal number of recipients per delivery via the virtual message delivery transport.
virtual_mailbox_limit (51200000)
The maximal size in bytes of an individual mailbox or maildir file, or zero (no limit).
MISCELLANEOUS CONTROLS
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf configuration files.
daemon_timeout (18000s)
How much time a Postfix daemon process may take to handle a request before it is terminated by
a built-in watchdog timer.
delay_logging_resolution_limit (2)
The maximal number of digits after the decimal point when logging sub-second delay values.
ipc_timeout (3600s)
The time limit for sending or receiving information over an internal communication channel.
max_idle (100s)
The maximum amount of time that an idle Postfix daemon process waits for an incoming connec-tion connection
tion before terminating voluntarily.
max_use (100)
The maximal number of incoming connections that a Postfix daemon process will service before
terminating voluntarily.
process_id (read-only)
The process ID of a Postfix command or daemon process.
process_name (read-only)
The process name of a Postfix command or daemon process.
queue_directory (see 'postconf -d' output)
The location of the Postfix top-level queue directory.
syslog_facility (mail)
The syslog facility of Postfix logging.
syslog_name (postfix)
The mail system name that is prepended to the process name in syslog records, so that "smtpd"
becomes, for example, "postfix/smtpd".
SEE ALSO
qmgr(8), queue manager
bounce(8), delivery status reports
postconf(5), configuration parameters
syslogd(8), system logging
README_FILES
Use "postconf readme_directory" or
"postconf html_directory" to locate this information.
VIRTUAL_README, domain hosting howto
LICENSE
The Secure Mailer license must be distributed with this software.
HISTORY
This delivery agent was originally based on the Postfix local delivery agent. Modifications mainly
consisted of removing code that either was not applicable or that was not safe in this context:
aliases, ~user/.forward files, delivery to "|command" or to /file/name.
The Delivered-To: message header appears in the qmail system by Daniel Bernstein.
The maildir structure appears in the qmail system by Daniel Bernstein.
AUTHOR(S)
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
Andrew McNamara
andrewm@connect.com.au
connect.com.au Pty. Ltd.
Level 3, 213 Miller St
North Sydney 2060, NSW, Australia
VIRTUAL(8)
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