    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 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 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 direc-
                  tory.

           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" com-
                  mand.  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 deliver-
                  ies to the same destination.

           round robin
                  The queue manager sorts delivery requests by desti-
                  nation.   Round-robin selection prevents one desti-
                  nation from dominating deliveries to other destina-
                  tions.

           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 cor-
                  rect per-message delays, using a sophisticated pre-
                  emptive 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 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  for-
                  ever.  The  action  is  to  start an incoming queue
                  scan.

           The qmgr(8) daemon reads an entire buffer worth  of  trig-
           gers.   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 environ-
           ment.

    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 trou-
           ble.

    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 "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  mas-
           ter.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_fil-
                  ter_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_recipi-
           ent_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_recipi-
           ent_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_recipi-
           ent_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_destina-
           tion_concurrency_limit)
                  Idem, for delivery via the named message transport.

           Available in Postfix version 2.5 and later:

           transport_initial_destination_concurrency ($initial_desti-
           nation_concurrency)
                  Initial concurrency for delivery via the named mes-
                  sage transport.

           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_destination_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 handshake failure.

           transport_destination_concurrency_negative_feedback
           ($default_destination_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 with-
                  out connection or handshake failure.

           transport_destination_concurrency_positive_feedback
           ($default_destination_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 performance analysis purposes.

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

           transport_destination_recipient_limit   ($default_destina-
           tion_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 scheduling algo-
                  rithm at all.

           transport_minimum_delivery_slots  ($default_minimum_deliv-
           ery_slots)
                  Idem, for delivery via the named message transport.

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

           transport_delivery_slot_discount          ($default_deliv-
           ery_slot_discount)
                  Idem, for delivery via the named message transport.

           default_delivery_slot_loan (3)
                  The  default  value  for transport-specific _deliv-
                  ery_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)
                  The maximal time a message is queued before  it  is
                  sent back as undeliverable.

           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 man-
                  ager 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.

           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 destina-
                  tion; the resulting behavior depends on  the  value
                  of   the  corresponding  per-destination  recipient
                  limit.

           transport_destination_rate_delay         $default_destina-
           tion_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 information over an internal  communication
                  channel.

    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  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 set-
                  tings, and provide 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  direc-
                  tory.

           syslog_facility (mail)
                  The syslog facility of Postfix logging.

           syslog_name (see 'postconf -d' output)
                  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
           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

                                                                           QMGR(8)