    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
           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 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
           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)
                  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.

           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_concur-
           rency_limit)
                  Idem, for delivery via the named message transport.

           Available in Postfix version 2.5 and later:

           transport_initial_destination_concurrency ($initial_destination_concur-
           rency)
                  Initial concurrency for delivery via the  named  message  trans-
                  port.

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

           transport_destination_concurrency_failed_cohort_limit  ($default_desti-
           nation_concurrency_failed_cohort_limit)
                  Idem, for delivery via the named message transport.

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

           transport_destination_concurrency_negative_feedback  ($default_destina-
           tion_concurrency_negative_feedback)
                  Idem, for delivery via the named message transport.

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

           transport_destination_concurrency_positive_feedback  ($default_destina-
           tion_concurrency_positive_feedback)
                  Idem, for delivery via the named message transport.

           destination_concurrency_feedback_debug (no)
                  Make  the queue manager's feedback algorithm verbose for perfor-
                  mance analysis purposes.

    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 (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 maxi-
                  mal_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 con-
                  tact 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
                  deliveries  to  the  same  destination;  the  resulting behavior
                  depends on the value of the corresponding per-destination recip-
                  ient limit.

           transport_destination_rate_delay $default_destination_rate_delay
                  Idem, for delivery via the named message transport.

           Available in Postfix version 3.1 and later:

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

           transport_transport_rate_delay $default_transport_rate_delay
                  Idem, for delivery via the named message 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 informa-
                  tion over an internal 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 con-
                  figuration files.

           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 log-
                  ging sub-second delay values.

           helpful_warnings (yes)
                  Log warnings about problematic configuration settings, and  pro-
                  vide helpful suggestions.

           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 example, "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.

    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
           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(8)