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QMGR(8)                                                                                              QMGR(8)



NAME
       qmgr - Postfix queue manager

SYNOPSIS
       qmgr [generic Postfix daemon options]

DESCRIPTION
       The  qmgr(8)  daemon  awaits  the  arrival of incoming mail and arranges for its delivery via Postfix
       delivery processes.  The actual mail routing strategy is delegated to the trivial-rewrite(8)  daemon.
       This program expects to be run from the master(8) process manager.

       Mail  addressed  to  the  local  double-bounce address is logged and discarded.  This stops potential
       loops caused by undeliverable bounce notifications.

MAIL QUEUES
       The qmgr(8) daemon maintains the following queues:

       incoming
              Inbound mail from the network, or mail picked up by the local pickup(8) daemon from the  mail-drop maildrop
              drop directory.

       active Messages  that the queue manager has opened for delivery. Only a limited number of messages is
              allowed to enter the active queue (leaky bucket strategy, for a fixed delivery rate).

       deferred
              Mail that could not be delivered upon the first attempt. The queue manager implements exponen-tial exponential
              tial backoff by doubling the time between delivery attempts.

       corrupt
              Unreadable or damaged queue files are moved here for inspection.

       hold   Messages that are kept "on hold" are kept here until someone sets them free.

DELIVERY STATUS REPORTS
       The  qmgr(8) daemon keeps an eye on per-message delivery status reports in the following directories.
       Each status report file has the same name as the corresponding message file:

       bounce Per-recipient status information about why mail is bounced.  These files are maintained by the
              bounce(8) daemon.

       defer  Per-recipient status information about why mail is delayed.  These files are maintained by the
              defer(8) daemon.

       trace  Per-recipient status information as requested with the Postfix "sendmail -v" or "sendmail -bv"
              command.  These files are maintained by the trace(8) daemon.

       The  qmgr(8)  daemon  is  responsible  for asking the bounce(8), defer(8) or trace(8) daemons to send
       delivery reports.

STRATEGIES
       The queue manager implements a variety of strategies for either opening queue files  (input)  or  for
       message delivery (output).

       leaky bucket
              This strategy limits the number of messages in the active queue and prevents the queue manager
              from running out of memory under heavy load.

       fairness
              When the active queue has room, the queue manager takes one message from  the  incoming  queue
              and one from the deferred queue. This prevents a large mail backlog from blocking the delivery
              of new mail.

       slow start
              This strategy eliminates "thundering herd" problems by slowly adjusting the number of parallel
              deliveries to the same destination.

       round robin
              The  queue manager sorts delivery requests by destination.  Round-robin selection prevents one
              destination from dominating deliveries to other destinations.

       exponential backoff
              Mail that cannot be delivered upon the first attempt is deferred.  The time  interval  between
              delivery attempts is doubled after each attempt.

       destination status cache
              The  queue manager avoids unnecessary delivery attempts by maintaining a short-term, in-memory
              list of unreachable destinations.

       preemptive message scheduling
              The queue manager attempts to minimize the average per-recipient delay while still  preserving
              the correct per-message delays, using a sophisticated preemptive message scheduling.

TRIGGERS
       On an idle system, the queue manager waits for the arrival of trigger events, or it waits for a timer
       to go off. A trigger is a one-byte message.  Depending on the message  received,  the  queue  manager
       performs  one  of the following actions (the message is followed by the symbolic constant used inter-nally internally
       nally by the software):

       D (QMGR_REQ_SCAN_DEFERRED)
              Start a deferred queue scan.  If a deferred queue scan is already in progress, that scan  will
              be restarted as soon as it finishes.

       I (QMGR_REQ_SCAN_INCOMING)
              Start an incoming queue scan. If an incoming queue scan is already in progress, that scan will
              be restarted as soon as it finishes.

       A (QMGR_REQ_SCAN_ALL)
              Ignore deferred queue file time stamps. The request affects the next deferred queue scan.

       F (QMGR_REQ_FLUSH_DEAD)
              Purge all information about dead transports and destinations.

       W (TRIGGER_REQ_WAKEUP)
              Wakeup call, This is used by the master server to instantiate servers that should not go  away
              forever. The action is to start an incoming queue scan.

       The qmgr(8) daemon reads an entire buffer worth of triggers.  Multiple identical trigger requests are
       collapsed into one, and trigger requests are sorted so that A and F precede D and I. Thus,  in  order
       to  force  a deferred queue run, one would request A F D; in order to notify the queue manager of the
       arrival of new mail one would request I.

STANDARDS
       RFC 3463 (Enhanced status codes)
       RFC 3464 (Delivery status notifications)

SECURITY
       The qmgr(8) daemon is not security sensitive. It reads single-character messages from untrusted local
       users,  and thus may be susceptible to denial of service attacks. The qmgr(8) daemon does not talk to
       the outside world, and it can be run at fixed low privilege in a chrooted environment.

DIAGNOSTICS
       Problems and transactions are logged to the syslog daemon.  Corrupted message files are saved to  the
       corrupt queue for further inspection.

       Depending  on  the setting of the notify_classes parameter, the postmaster is notified of bounces and
       of other trouble.

BUGS
       A single queue manager process has to compete for disk access with multiple front-end processes  such
       as cleanup(8). A sudden burst of inbound mail can negatively impact outbound delivery rates.

CONFIGURATION PARAMETERS
       Changes to main.cf are not picked up automatically as qmgr(8) is a persistent process. Use the "post-fix "postfix
       fix reload" command after a configuration change.

       The text below provides only a parameter summary. See postconf(5) for more  details  including  exam-ples. examples.
       ples.

       In the text below, transport is the first field in a master.cf entry.

COMPATIBILITY CONTROLS
       allow_min_user (no)
              Allow a recipient address to have `-' as the first character.

ACTIVE QUEUE CONTROLS
       qmgr_clog_warn_time (300s)
              The  minimal  delay  between  warnings  that a specific destination is clogging up the Postfix
              active queue.

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

       qmgr_message_recipient_limit (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 (10)
              The minimal number of in-memory recipients for any message.

       default_recipient_limit (20000)
              The default per-transport upper limit on the number of in-memory recipients.

       transport_recipient_limit ($default_recipient_limit)
              Idem, for delivery via the named message transport.

       default_extra_recipient_limit (1000)
              The default value for the extra per-transport limit imposed on the number of in-memory recipi-ents. recipients.
              ents.

       transport_extra_recipient_limit ($default_extra_recipient_limit)
              Idem, for delivery via the named message transport.

       Available in Postfix version 2.4 and later:

       default_recipient_refill_limit (100)
              The default per-transport limit on the number of recipients refilled at once.

       transport_recipient_refill_limit ($default_recipient_refill_limit)
              Idem, for delivery via the named message transport.

       default_recipient_refill_delay (5s)
              The default per-transport maximum delay between recipients refills.

       transport_recipient_refill_delay ($default_recipient_refill_delay)
              Idem, for delivery via the named message transport.

DELIVERY CONCURRENCY CONTROLS
       initial_destination_concurrency (5)
              The initial per-destination concurrency level for parallel delivery to the same destination.

       default_destination_concurrency_limit (20)
              The default maximal number of parallel deliveries to the same destination.

       transport_destination_concurrency_limit ($default_destination_concurrency_limit)
              Idem, for delivery via the named message transport.

RECIPIENT SCHEDULING CONTROLS
       default_destination_recipient_limit (50)
              The default maximal number of recipients per message delivery.

       transport_destination_recipient_limit ($default_destination_recipient_limit)
              Idem, for delivery via the named message transport.

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

       transport_delivery_slot_cost ($default_delivery_slot_cost)
              Idem, for delivery via the named message transport.

       default_minimum_delivery_slots (3)
              How  many recipients a message must have in order to invoke the Postfix queue manager's sched-uling scheduling
              uling algorithm at all.

       transport_minimum_delivery_slots ($default_minimum_delivery_slots)
              Idem, for delivery via the named message transport.

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

       transport_delivery_slot_discount ($default_delivery_slot_discount)
              Idem, for delivery via the named message transport.

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

       transport_delivery_slot_loan ($default_delivery_slot_loan)
              Idem, for delivery via the named message transport.

OTHER RESOURCE AND RATE CONTROLS
       minimal_backoff_time (version dependent)
              The minimal time between attempts to deliver a deferred message.

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

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

       queue_run_delay (version dependent)
              The time between deferred queue scans by the queue manager.

       transport_retry_time (60s)
              The time between attempts by the Postfix queue manager to  contact  a  malfunctioning  message
              delivery transport.

       Available in Postfix version 2.1 and later:

       bounce_queue_lifetime (5d)
              The maximal time a bounce message is queued before it is considered undeliverable.

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.

       defer_transports (empty)
              The names of message delivery transports that should not deliver mail  unless  someone  issues
              "sendmail -q" or equivalent.

       delay_logging_resolution_limit (2)
              The maximal number of digits after the decimal point when logging sub-second delay values.

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

       ipc_timeout (3600s)
              The time limit for sending or receiving information over an internal communication channel.

       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".

FILES
       /var/spool/postfix/incoming, incoming queue
       /var/spool/postfix/active, active queue
       /var/spool/postfix/deferred, deferred queue
       /var/spool/postfix/bounce, non-delivery status
       /var/spool/postfix/defer, non-delivery status
       /var/spool/postfix/trace, delivery status

SEE ALSO
       trivial-rewrite(8), address routing
       bounce(8), delivery status reports
       postconf(5), configuration parameters
       master(5), generic daemon options
       master(8), process manager
       syslogd(8), system logging

README FILES
       Use "postconf readme_directory" or "postconf html_directory" to locate this information.
       SCHEDULER_README, scheduling algorithm
       QSHAPE_README, Postfix queue analysis

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

       Scheduler enhancements:
       Patrik Rak
       Modra 6
       155 00, Prague, Czech Republic



                                                                                                     QMGR(8)

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