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QMGR(8postfix)                                                                     QMGR(8postfix)

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  triv-
       ial-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 po-
       tential 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 imple-
              ments 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 main-
              tained by the bounce(8) daemon.

       defer  Per-recipient status information about why mail is delayed.  These files are  main-
              tained 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 (in-
       put) 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 incom-
              ing 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 inter-
              val 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  re-
       ceived,  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
       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 un-
       trusted 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  syslogd(8)  or  postlogd(8).   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 pro-
       cesses  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 "postfix reload" command after a configuration change.

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

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

COMPATIBILITY CONTROLS
       Available before Postfix version 2.5:

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

       Available with Postfix version 2.7 and later:

       default_filter_nexthop (empty)
              When a content_filter or FILTER request specifies no explicit next-hop destination,
              use  $default_filter_nexthop  instead;  when that value is empty, use the domain in
              the recipient address.

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 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)
              A transport-specific override  for  the  default_recipient_limit  parameter  value,
              where transport is the master.cf name of the message delivery 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)
              A  transport-specific  override  for  the  default_extra_recipient_limit  parameter
              value, where transport is the master.cf name of the message delivery 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)
              A  transport-specific  override  for  the  default_recipient_refill_limit parameter
              value, where transport is the master.cf name of the message delivery transport.

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

       transport_recipient_refill_delay ($default_recipient_refill_delay)
              A transport-specific  override  for  the  default_recipient_refill_delay  parameter
              value, where transport is the master.cf name of the message delivery 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)
              A transport-specific override for the default_destination_concurrency_limit parame-
              ter value, where transport is the master.cf name of the message delivery transport.

       Available in Postfix version 2.5 and later:

       transport_initial_destination_concurrency ($initial_destination_concurrency)
              A  transport-specific  override  for  the initial_destination_concurrency parameter
              value, where transport is the master.cf name of the message delivery transport.

       default_destination_concurrency_failed_cohort_limit (1)
              How many pseudo-cohorts must suffer connection or handshake failure before  a  spe-
              cific destination is considered unavailable (and further delivery is suspended).

       transport_destination_concurrency_failed_cohort_limit        ($default_destination_concur-
       rency_failed_cohort_limit)
              A transport-specific override  for  the  default_destination_concurrency_failed_co-
              hort_limit  parameter  value,  where transport is the master.cf name of the message
              delivery transport.

       default_destination_concurrency_negative_feedback (1)
              The per-destination amount of delivery concurrency negative feedback, after  a  de-
              livery completes with a connection or handshake failure.

       transport_destination_concurrency_negative_feedback ($default_destination_concurrency_neg-
       ative_feedback)
              A  transport-specific  override   for   the   default_destination_concurrency_nega-
              tive_feedback parameter value, where transport is the master.cf name of the message
              delivery transport.

       default_destination_concurrency_positive_feedback (1)
              The per-destination amount of delivery concurrency positive feedback, after  a  de-
              livery completes without connection or handshake failure.

       transport_destination_concurrency_positive_feedback ($default_destination_concurrency_pos-
       itive_feedback)
              A  transport-specific  override   for   the   default_destination_concurrency_posi-
              tive_feedback parameter value, where transport is the master.cf name of the message
              delivery transport.

       destination_concurrency_feedback_debug (no)
              Make the queue manager's feedback algorithm verbose for performance  analysis  pur-
              poses.

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)
              A transport-specific override for the default_destination_recipient_limit parameter
              value, where transport is the master.cf name of the message delivery 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)
              A  transport-specific  override for the default_delivery_slot_cost parameter value,
              where transport is the master.cf name of the message delivery transport.

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

       transport_minimum_delivery_slots ($default_minimum_delivery_slots)
              A  transport-specific  override  for  the  default_minimum_delivery_slots parameter
              value, where transport is the master.cf name of the message delivery transport.

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

       transport_delivery_slot_discount ($default_delivery_slot_discount)
              A transport-specific  override  for  the  default_delivery_slot_discount  parameter
              value, where transport is the master.cf name of the message delivery transport.

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

       transport_delivery_slot_loan ($default_delivery_slot_loan)
              A  transport-specific  override for the default_delivery_slot_loan parameter value,
              where transport is the master.cf name of the message delivery transport.

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

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

       maximal_queue_lifetime (5d)
              Consider  a  message  as undeliverable, when delivery fails with a temporary error,
              and the time in the queue has reached the maximal_queue_lifetime limit.

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

       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)
              Consider a bounce message as undeliverable, when delivery fails  with  a  temporary
              error, and the time in the queue has reached the bounce_queue_lifetime limit.

       Available in Postfix version 2.5 and later:

       default_destination_rate_delay (0s)
              The  default amount of delay that is inserted between individual message deliveries
              to the same destination and over the same message delivery transport.

       transport_destination_rate_delay ($default_destination_rate_delay)
              A transport-specific  override  for  the  default_destination_rate_delay  parameter
              value, where transport is the master.cf name of the message delivery transport.

       Available in Postfix version 3.1 and later:

       default_transport_rate_delay (0s)
              The  default amount of delay that is inserted between individual message deliveries
              over the same message delivery transport, regardless of destination.

       transport_transport_rate_delay ($default_transport_rate_delay)
              A transport-specific override for the default_transport_rate_delay parameter value,
              where the initial transport in the parameter name is the master.cf name of the mes-
              sage delivery transport.

SAFETY CONTROLS
       qmgr_daemon_timeout (1000s)
              How much time a Postfix queue manager process may take to handle a  request  before
              it is terminated by a built-in watchdog timer.

       qmgr_ipc_timeout (60s)
              The  time limit for the queue manager to send or receive information over an inter-
              nal communication channel.

       Available in Postfix version 3.1 and later:

       address_verify_pending_request_limit (see 'postconf -d' output)
              A safety limit that prevents address verification requests  from  overwhelming  the
              Postfix queue.

MISCELLANEOUS CONTROLS
       config_directory (see 'postconf -d' output)
              The default location of the Postfix main.cf and master.cf configuration files.

       defer_transports (empty)
              The  names of message delivery transports that should not deliver mail unless some-
              one 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 sugges-
              tions.

       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 (see 'postconf -d' output)
              A prefix that is prepended to the process name in syslog records, so that, for  ex-
              ample, "smtpd" becomes "prefix/smtpd".

       Available in Postfix version 3.0 and later:

       confirm_delay_cleared (no)
              After  sending a "your message is delayed" notification, inform the sender when the
              delay clears up.

       Available in Postfix 3.3 and later:

       service_name (read-only)
              The master.cf service name of a Postfix daemon process.

       Available in Postfix 3.5 and later:

       info_log_address_format (external)
              The email address form that will be  used  in  non-debug  logging  (info,  warning,
              etc.).

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
       postlogd(8), Postfix logging
       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

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

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA

                                                                                   QMGR(8postfix)

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