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QMGR(8) 		     System Manager's Manual			 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 maildrop directory.

     active Messages that the queue manager has opened for delivery. Only a lim-
	    ited  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.

     corruptUnreadable 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  pre-
	    vents a large mail backlog from blocking the delivery of new mail.

     slow start
	    This  strategy  eliminates	"thundering herd" problems by slowly ad-
	    justing 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 de-
	    liveries 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  maintain-
	    ing a short-term, in-memory list of unreachable destinations.

     preemptive message scheduling
	    The queue manager attempts to minimize the average per-recipient de-
	    lay  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
     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 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).  Cor-
     rupted 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 persis-
     tent 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 charac-
	    ter.

     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 re-
	    cipients.

     transport_recipient_limit ($default_recipient_limit)
	    A  transport-specific override for the default_recipient_limit para-
	    meter 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 mes-
	    sage 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  mes-
	    sage delivery transport.

     default_recipient_refill_delay (5s)
	    The  default  per-transport  maximum delay between refilling recipi-
	    ents.

     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  mes-
	    sage 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 desti-
	    nation.

     transport_destination_concurrency_limit ($default_destination_concur-
     rency_limit)
	    A transport-specific override  for	the  default_destination_concur-
	    rency_limit  parameter  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_concur-
     rency)
	    A transport-specific override  for	the  initial_destination_concur-
	    rency  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 specific destination is considered unavailable (and further
	    delivery is suspended).

     transport_destination_concurrency_failed_cohort_limit ($default_destina-
     tion_concurrency_failed_cohort_limit)
	    A  transport-specific  override  for the default_destination_concur-
	    rency_failed_cohort_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 feed-
	    back, after a delivery completes  with  a  connection  or  handshake
	    failure.

     transport_destination_concurrency_negative_feedback ($default_destina-
     tion_concurrency_negative_feedback)
	    A  transport-specific  override  for the default_destination_concur-
	    rency_negative_feedback parameter value, where transport is the mas-
	    ter.cf name of the message delivery transport.

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

     transport_destination_concurrency_positive_feedback ($default_destina-
     tion_concurrency_positive_feedback)
	    A transport-specific override  for	the  default_destination_concur-
	    rency_positive_feedback parameter value, where transport is the mas-
	    ter.cf name of the message delivery 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 message delivery.

     transport_destination_recipient_limit ($default_destination_recipi-
     ent_limit)
	    A transport-specific override  for	the  default_destination_recipi-
	    ent_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  pre-
	    empt delivery of one message with another.

     transport_delivery_slot_cost ($default_delivery_slot_cost)
	    A transport-specific override for the default_delivery_slot_cost pa-
	    rameter  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 Post-
	    fix queue manager'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  mes-
	    sage 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  mes-
	    sage delivery transport.

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

     transport_delivery_slot_loan ($default_delivery_slot_loan)
	    A transport-specific override for the default_delivery_slot_loan pa-
	    rameter 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 tem-
	    porary 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 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 mes-
	    sage  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  mes-
	    sage 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 mes-
	    sage 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 message 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 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 configura-
	    tion 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
	    delay values.

     helpful_warnings (yes)
	    Log warnings about problematic configuration settings,  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 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.

     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(8)
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