.\"	$NetBSD: qmgr.8,v 1.2.14.1 2023/12/25 12:54:41 martin Exp $
.\"
.TH QMGR 8 
.ad
.fi
.SH NAME
qmgr
\-
Postfix queue manager
.SH "SYNOPSIS"
.na
.nf
\fBqmgr\fR [generic Postfix daemon options]
.SH DESCRIPTION
.ad
.fi
The \fBqmgr\fR(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
\fBtrivial\-rewrite\fR(8) daemon.
This program expects to be run from the \fBmaster\fR(8) process
manager.

Mail addressed to the local \fBdouble\-bounce\fR address is
logged and discarded.  This stops potential loops caused by
undeliverable bounce notifications.
.SH "MAIL QUEUES"
.na
.nf
.ad
.fi
The \fBqmgr\fR(8) daemon maintains the following queues:
.IP \fBincoming\fR
Inbound mail from the network, or mail picked up by the
local \fBpickup\fR(8) daemon from the \fBmaildrop\fR directory.
.IP \fBactive\fR
Messages that the queue manager has opened for delivery. Only
a limited number of messages is allowed to enter the \fBactive\fR
queue (leaky bucket strategy, for a fixed delivery rate).
.IP \fBdeferred\fR
Mail that could not be delivered upon the first attempt. The queue
manager implements exponential backoff by doubling the time between
delivery attempts.
.IP \fBcorrupt\fR
Unreadable or damaged queue files are moved here for inspection.
.IP \fBhold\fR
Messages that are kept "on hold" are kept here until someone
sets them free.
.SH "DELIVERY STATUS REPORTS"
.na
.nf
.ad
.fi
The \fBqmgr\fR(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:
.IP \fBbounce\fR
Per\-recipient status information about why mail is bounced.
These files are maintained by the \fBbounce\fR(8) daemon.
.IP \fBdefer\fR
Per\-recipient status information about why mail is delayed.
These files are maintained by the \fBdefer\fR(8) daemon.
.IP \fBtrace\fR
Per\-recipient status information as requested with the
Postfix "\fBsendmail \-v\fR" or "\fBsendmail \-bv\fR" command.
These files are maintained by the \fBtrace\fR(8) daemon.
.PP
The \fBqmgr\fR(8) daemon is responsible for asking the
\fBbounce\fR(8), \fBdefer\fR(8) or \fBtrace\fR(8) daemons to
send delivery reports.
.SH "STRATEGIES"
.na
.nf
.ad
.fi
The queue manager implements a variety of strategies for
either opening queue files (input) or for message delivery (output).
.IP "\fBleaky bucket\fR"
This strategy limits the number of messages in the \fBactive\fR queue
and prevents the queue manager from running out of memory under
heavy load.
.IP \fBfairness\fR
When the \fBactive\fR queue has room, the queue manager takes one
message from the \fBincoming\fR queue and one from the \fBdeferred\fR
queue. This prevents a large mail backlog from blocking the delivery
of new mail.
.IP "\fBslow start\fR"
This strategy eliminates "thundering herd" problems by slowly
adjusting the number of parallel deliveries to the same destination.
.IP "\fBround robin\fR"
The queue manager sorts delivery requests by destination.
Round\-robin selection prevents one destination from dominating
deliveries to other destinations.
.IP "\fBexponential backoff\fR"
Mail that cannot be delivered upon the first attempt is deferred.
The time interval between delivery attempts is doubled after each
attempt.
.IP "\fBdestination status cache\fR"
The queue manager avoids unnecessary delivery attempts by
maintaining a short\-term, in\-memory list of unreachable destinations.
.IP "\fBpreemptive message scheduling\fR"
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.
.SH "TRIGGERS"
.na
.nf
.ad
.fi
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):
.IP "\fBD (QMGR_REQ_SCAN_DEFERRED)\fR"
Start a deferred queue scan.  If a deferred queue scan is already
in progress, that scan will be restarted as soon as it finishes.
.IP "\fBI (QMGR_REQ_SCAN_INCOMING)\fR"
Start an incoming queue scan. If an incoming queue scan is already
in progress, that scan will be restarted as soon as it finishes.
.IP "\fBA (QMGR_REQ_SCAN_ALL)\fR"
Ignore deferred queue file time stamps. The request affects
the next deferred queue scan.
.IP "\fBF (QMGR_REQ_FLUSH_DEAD)\fR"
Purge all information about dead transports and destinations.
.IP "\fBW (TRIGGER_REQ_WAKEUP)\fR"
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.
.PP
The \fBqmgr\fR(8) daemon reads an entire buffer worth of triggers.
Multiple identical trigger requests are collapsed into one, and
trigger requests are sorted so that \fBA\fR and \fBF\fR precede
\fBD\fR and \fBI\fR. Thus, in order to force a deferred queue run,
one would request \fBA F D\fR; in order to notify the queue manager
of the arrival of new mail one would request \fBI\fR.
.SH "STANDARDS"
.na
.nf
RFC 3463 (Enhanced status codes)
RFC 3464 (Delivery status notifications)
.SH "SECURITY"
.na
.nf
.ad
.fi
The \fBqmgr\fR(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 \fBqmgr\fR(8) daemon
does not talk to the outside world, and it can be run at fixed low
privilege in a chrooted environment.
.SH DIAGNOSTICS
.ad
.fi
Problems and transactions are logged to \fBsyslogd\fR(8)
or \fBpostlogd\fR(8).
Corrupted message files are saved to the \fBcorrupt\fR queue
for further inspection.

Depending on the setting of the \fBnotify_classes\fR parameter,
the postmaster is notified of bounces and of other trouble.
.SH BUGS
.ad
.fi
A single queue manager process has to compete for disk access with
multiple front\-end processes such as \fBcleanup\fR(8). A sudden burst of
inbound mail can negatively impact outbound delivery rates.
.SH "CONFIGURATION PARAMETERS"
.na
.nf
.ad
.fi
Changes to \fBmain.cf\fR are not picked up automatically
as \fBqmgr\fR(8)
is a persistent process. Use the "\fBpostfix reload\fR" command after
a configuration change.

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

In the text below, \fItransport\fR is the first field in a
\fBmaster.cf\fR entry.
.SH "COMPATIBILITY CONTROLS"
.na
.nf
.ad
.fi
Available before Postfix version 2.5:
.IP "\fBallow_min_user (no)\fR"
Allow a sender or recipient address to have `\-' as the first
character.
.PP
Available with Postfix version 2.7 and later:
.IP "\fBdefault_filter_nexthop (empty)\fR"
When a content_filter or FILTER request specifies no explicit
next\-hop destination, use $default_filter_nexthop instead; when
that value is empty, use the domain in the recipient address.
.SH "ACTIVE QUEUE CONTROLS"
.na
.nf
.ad
.fi
.IP "\fBqmgr_clog_warn_time (300s)\fR"
The minimal delay between warnings that a specific destination is
clogging up the Postfix active queue.
.IP "\fBqmgr_message_active_limit (20000)\fR"
The maximal number of messages in the active queue.
.IP "\fBqmgr_message_recipient_limit (20000)\fR"
The maximal number of recipients held in memory by the Postfix
queue manager, and the maximal size of the short\-term,
in\-memory "dead" destination status cache.
.IP "\fBqmgr_message_recipient_minimum (10)\fR"
The minimal number of in\-memory recipients for any message.
.IP "\fBdefault_recipient_limit (20000)\fR"
The default per\-transport upper limit on the number of in\-memory
recipients.
.IP "\fBtransport_recipient_limit ($default_recipient_limit)\fR"
A transport\-specific override for the default_recipient_limit
parameter value, where \fItransport\fR is the master.cf name of
the message delivery transport.
.IP "\fBdefault_extra_recipient_limit (1000)\fR"
The default value for the extra per\-transport limit imposed on the
number of in\-memory recipients.
.IP "\fBtransport_extra_recipient_limit ($default_extra_recipient_limit)\fR"
A transport\-specific override for the default_extra_recipient_limit
parameter value, where \fItransport\fR is the master.cf name of
the message delivery transport.
.PP
Available in Postfix version 2.4 and later:
.IP "\fBdefault_recipient_refill_limit (100)\fR"
The default per\-transport limit on the number of recipients refilled at
once.
.IP "\fBtransport_recipient_refill_limit ($default_recipient_refill_limit)\fR"
A transport\-specific override for the default_recipient_refill_limit
parameter value, where \fItransport\fR is the master.cf name of
the message delivery transport.
.IP "\fBdefault_recipient_refill_delay (5s)\fR"
The default per\-transport maximum delay between recipients refills.
.IP "\fBtransport_recipient_refill_delay ($default_recipient_refill_delay)\fR"
A transport\-specific override for the default_recipient_refill_delay
parameter value, where \fItransport\fR is the master.cf name of
the message delivery transport.
.SH "DELIVERY CONCURRENCY CONTROLS"
.na
.nf
.ad
.fi
.IP "\fBinitial_destination_concurrency (5)\fR"
The initial per\-destination concurrency level for parallel delivery
to the same destination.
.IP "\fBdefault_destination_concurrency_limit (20)\fR"
The default maximal number of parallel deliveries to the same
destination.
.IP "\fBtransport_destination_concurrency_limit ($default_destination_concurrency_limit)\fR"
A transport\-specific override for the
default_destination_concurrency_limit parameter value, where
\fItransport\fR is the master.cf name of the message delivery
transport.
.PP
Available in Postfix version 2.5 and later:
.IP "\fBtransport_initial_destination_concurrency ($initial_destination_concurrency)\fR"
A transport\-specific override for the initial_destination_concurrency
parameter value, where \fItransport\fR is the master.cf name of
the message delivery transport.
.IP "\fBdefault_destination_concurrency_failed_cohort_limit (1)\fR"
How many pseudo\-cohorts must suffer connection or handshake
failure before a specific destination is considered unavailable
(and further delivery is suspended).
.IP "\fBtransport_destination_concurrency_failed_cohort_limit ($default_destination_concurrency_failed_cohort_limit)\fR"
A transport\-specific override for the
default_destination_concurrency_failed_cohort_limit parameter value,
where \fItransport\fR is the master.cf name of the message delivery
transport.
.IP "\fBdefault_destination_concurrency_negative_feedback (1)\fR"
The per\-destination amount of delivery concurrency negative
feedback, after a delivery completes with a connection or handshake
failure.
.IP "\fBtransport_destination_concurrency_negative_feedback ($default_destination_concurrency_negative_feedback)\fR"
A transport\-specific override for the
default_destination_concurrency_negative_feedback parameter value,
where \fItransport\fR is the master.cf name of the message delivery
transport.
.IP "\fBdefault_destination_concurrency_positive_feedback (1)\fR"
The per\-destination amount of delivery concurrency positive
feedback, after a delivery completes without connection or handshake
failure.
.IP "\fBtransport_destination_concurrency_positive_feedback ($default_destination_concurrency_positive_feedback)\fR"
A transport\-specific override for the
default_destination_concurrency_positive_feedback parameter value,
where \fItransport\fR is the master.cf name of the message delivery
transport.
.IP "\fBdestination_concurrency_feedback_debug (no)\fR"
Make the queue manager's feedback algorithm verbose for performance
analysis purposes.
.SH "RECIPIENT SCHEDULING CONTROLS"
.na
.nf
.ad
.fi
.IP "\fBdefault_destination_recipient_limit (50)\fR"
The default maximal number of recipients per message delivery.
.IP "\fBtransport_destination_recipient_limit ($default_destination_recipient_limit)\fR"
A transport\-specific override for the
default_destination_recipient_limit parameter value, where
\fItransport\fR is the master.cf name of the message delivery
transport.
.SH "MESSAGE SCHEDULING CONTROLS"
.na
.nf
.ad
.fi
.IP "\fBdefault_delivery_slot_cost (5)\fR"
How often the Postfix queue manager's scheduler is allowed to
preempt delivery of one message with another.
.IP "\fBtransport_delivery_slot_cost ($default_delivery_slot_cost)\fR"
A transport\-specific override for the default_delivery_slot_cost
parameter value, where \fItransport\fR is the master.cf name of
the message delivery transport.
.IP "\fBdefault_minimum_delivery_slots (3)\fR"
How many recipients a message must have in order to invoke the
Postfix queue manager's scheduling algorithm at all.
.IP "\fBtransport_minimum_delivery_slots ($default_minimum_delivery_slots)\fR"
A transport\-specific override for the default_minimum_delivery_slots
parameter value, where \fItransport\fR is the master.cf name of
the message delivery transport.
.IP "\fBdefault_delivery_slot_discount (50)\fR"
The default value for transport\-specific _delivery_slot_discount
settings.
.IP "\fBtransport_delivery_slot_discount ($default_delivery_slot_discount)\fR"
A transport\-specific override for the default_delivery_slot_discount
parameter value, where \fItransport\fR is the master.cf name of
the message delivery transport.
.IP "\fBdefault_delivery_slot_loan (3)\fR"
The default value for transport\-specific _delivery_slot_loan
settings.
.IP "\fBtransport_delivery_slot_loan ($default_delivery_slot_loan)\fR"
A transport\-specific override for the default_delivery_slot_loan
parameter value, where \fItransport\fR is the master.cf name of
the message delivery transport.
.SH "OTHER RESOURCE AND RATE CONTROLS"
.na
.nf
.ad
.fi
.IP "\fBminimal_backoff_time (300s)\fR"
The minimal time between attempts to deliver a deferred message;
prior to Postfix 2.4 the default value was 1000s.
.IP "\fBmaximal_backoff_time (4000s)\fR"
The maximal time between attempts to deliver a deferred message.
.IP "\fBmaximal_queue_lifetime (5d)\fR"
Consider a message as undeliverable, when delivery fails with a
temporary error, and the time in the queue has reached the
maximal_queue_lifetime limit.
.IP "\fBqueue_run_delay (300s)\fR"
The time between deferred queue scans by the queue manager;
prior to Postfix 2.4 the default value was 1000s.
.IP "\fBtransport_retry_time (60s)\fR"
The time between attempts by the Postfix queue manager to contact
a malfunctioning message delivery transport.
.PP
Available in Postfix version 2.1 and later:
.IP "\fBbounce_queue_lifetime (5d)\fR"
Consider a bounce message as undeliverable, when delivery fails
with a temporary error, and the time in the queue has reached the
bounce_queue_lifetime limit.
.PP
Available in Postfix version 2.5 and later:
.IP "\fBdefault_destination_rate_delay (0s)\fR"
The default amount of delay that is inserted between individual
message deliveries to the same destination and over the same message
delivery transport.
.IP "\fBtransport_destination_rate_delay ($default_destination_rate_delay)\fR"
A transport\-specific override for the default_destination_rate_delay
parameter value, where \fItransport\fR is the master.cf name of
the message delivery transport.
.PP
Available in Postfix version 3.1 and later:
.IP "\fBdefault_transport_rate_delay (0s)\fR"
The default amount of delay that is inserted between individual
message deliveries over the same message delivery transport,
regardless of destination.
.IP "\fBtransport_transport_rate_delay ($default_transport_rate_delay)\fR"
A transport\-specific override for the default_transport_rate_delay
parameter value, where the initial \fItransport\fR in the parameter
name is the master.cf name of the message delivery transport.
.SH "SAFETY CONTROLS"
.na
.nf
.ad
.fi
.IP "\fBqmgr_daemon_timeout (1000s)\fR"
How much time a Postfix queue manager process may take to handle
a request before it is terminated by a built\-in watchdog timer.
.IP "\fBqmgr_ipc_timeout (60s)\fR"
The time limit for the queue manager to send or receive information
over an internal communication channel.
.PP
Available in Postfix version 3.1 and later:
.IP "\fBaddress_verify_pending_request_limit (see 'postconf -d' output)\fR"
A safety limit that prevents address verification requests from
overwhelming the Postfix queue.
.SH "MISCELLANEOUS CONTROLS"
.na
.nf
.ad
.fi
.IP "\fBconfig_directory (see 'postconf -d' output)\fR"
The default location of the Postfix main.cf and master.cf
configuration files.
.IP "\fBdefer_transports (empty)\fR"
The names of message delivery transports that should not deliver mail
unless someone issues "\fBsendmail \-q\fR" or equivalent.
.IP "\fBdelay_logging_resolution_limit (2)\fR"
The maximal number of digits after the decimal point when logging
sub\-second delay values.
.IP "\fBhelpful_warnings (yes)\fR"
Log warnings about problematic configuration settings, and provide
helpful suggestions.
.IP "\fBprocess_id (read\-only)\fR"
The process ID of a Postfix command or daemon process.
.IP "\fBprocess_name (read\-only)\fR"
The process name of a Postfix command or daemon process.
.IP "\fBqueue_directory (see 'postconf -d' output)\fR"
The location of the Postfix top\-level queue directory.
.IP "\fBsyslog_facility (mail)\fR"
The syslog facility of Postfix logging.
.IP "\fBsyslog_name (see 'postconf -d' output)\fR"
A prefix that is prepended to the process name in syslog
records, so that, for example, "smtpd" becomes "prefix/smtpd".
.PP
Available in Postfix version 3.0 and later:
.IP "\fBconfirm_delay_cleared (no)\fR"
After sending a "your message is delayed" notification, inform
the sender when the delay clears up.
.PP
Available in Postfix 3.3 and later:
.IP "\fBservice_name (read\-only)\fR"
The master.cf service name of a Postfix daemon process.
.PP
Available in Postfix 3.5 and later:
.IP "\fBinfo_log_address_format (external)\fR"
The email address form that will be used in non\-debug logging
(info, warning, etc.).
.SH "FILES"
.na
.nf
/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
.SH "SEE ALSO"
.na
.nf
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
.SH "README FILES"
.na
.nf
.ad
.fi
Use "\fBpostconf readme_directory\fR" or
"\fBpostconf html_directory\fR" to locate this information.
.na
.nf
SCHEDULER_README, scheduling algorithm
QSHAPE_README, Postfix queue analysis
.SH "LICENSE"
.na
.nf
.ad
.fi
The Secure Mailer license must be distributed with this software.
.SH "AUTHOR(S)"
.na
.nf
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