qmgr



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  dis-
       carded.   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 maildrop 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 exponential  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  main-
              tained 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 mes-
              sage 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 destina-
              tion.

       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 dou-
              bled after each attempt.

       destination status cache
              The queue manager avoids unnecessary delivery attempts by  main-
              taining  a  short-term,  in-memory  list of unreachable destina-
              tions.

       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 mes-
       sage.  Depending on the message received, the  queue  manager  performs
       one  of  the following actions (the message is followed by the symbolic
       constant used internally 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

       None. The qmgr(8) daemon does not interact with the outside world.


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 out-
       side 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  postmas-
       ter is notified of bounces and of other trouble.


BUGS

       A single queue manager process has to compete for disk access with mul-
       tiple 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 per-
       sistent process. Use the "postfix reload" command after a configuration
       change.

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

       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 (10000)
              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 recipients.

       transport_extra_recipient_limit ($default_extra_recipient_limit)
              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_concur-
       rency_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_recipi-
       ent_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 scheduling 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 (1000s)
              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 (1000s)
              The time between deferred queue scans by the queue manager.

       transport_retry_time (60s)
              The time between attempts by the Postfix queue manager  to  con-
              tact 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 consid-
              ered undeliverable.


MISCELLANEOUS CONTROLS

       config_directory (see postconf -d output)
              The default location of the Postfix main.cf and  master.cf  con-
              figuration 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  be
              delivered  to unless someone issues "sendmail -q" or equivalent.

       helpful_warnings (yes)
              Log warnings about problematic configuration settings, and  pro-
              vide 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, "post-
              fix/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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