1QMGR(8) System Manager's Manual QMGR(8)
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6 qmgr - Postfix queue manager
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9 qmgr [generic Postfix daemon options]
10
12 The qmgr(8) daemon awaits the arrival of incoming mail and arranges for
13 its delivery via Postfix delivery processes. The actual mail routing
14 strategy is delegated to the trivial-rewrite(8) daemon. This program
15 expects to be run from the master(8) process manager.
16 Mail addressed to the local double-bounce address is logged and dis‐
18 carded. This stops potential loops caused by undeliverable bounce
19 notifications.
20
22 The qmgr(8) daemon maintains the following queues:
23 incoming
25 Inbound mail from the network, or mail picked up by the local
26 pickup(8) daemon from the maildrop directory.
27 active Messages that the queue manager has opened for delivery. Only a
29 limited number of messages is allowed to enter the active queue
30 (leaky bucket strategy, for a fixed delivery rate).
31 deferred
33 Mail that could not be delivered upon the first attempt. The
34 queue manager implements exponential backoff by doubling the
35 time between delivery attempts.
36 corrupt
38 Unreadable or damaged queue files are moved here for inspection.
39 hold Messages that are kept "on hold" are kept here until someone
41 sets them free.
42
44 The qmgr(8) daemon keeps an eye on per-message delivery status reports
45 in the following directories. Each status report file has the same name
46 as the corresponding message file:
47 bounce Per-recipient status information about why mail is bounced.
49 These files are maintained by the bounce(8) daemon.
50 defer Per-recipient status information about why mail is delayed.
52 These files are maintained by the defer(8) daemon.
53 trace Per-recipient status information as requested with the Postfix
55 "sendmail -v" or "sendmail -bv" command. These files are main‐
56 tained by the trace(8) daemon.
57 The qmgr(8) daemon is responsible for asking the bounce(8), defer(8) or
59 trace(8) daemons to send delivery reports.
60
62 The queue manager implements a variety of strategies for either opening
63 queue files (input) or for message delivery (output).
64 leaky bucket
66 This strategy limits the number of messages in the active queue
67 and prevents the queue manager from running out of memory under
68 heavy load.
69 fairness
71 When the active queue has room, the queue manager takes one mes‐
72 sage from the incoming queue and one from the deferred queue.
73 This prevents a large mail backlog from blocking the delivery of
74 new mail.
75 slow start
77 This strategy eliminates "thundering herd" problems by slowly
78 adjusting the number of parallel deliveries to the same destina‐
79 tion.
80 round robin
82 The queue manager sorts delivery requests by destination.
83 Round-robin selection prevents one destination from dominating
84 deliveries to other destinations.
85 exponential backoff
87 Mail that cannot be delivered upon the first attempt is
88 deferred. The time interval between delivery attempts is dou‐
89 bled after each attempt.
90 destination status cache
92 The queue manager avoids unnecessary delivery attempts by main‐
93 taining a short-term, in-memory list of unreachable destina‐
94 tions.
95 preemptive message scheduling
97 The queue manager attempts to minimize the average per-recipient
98 delay while still preserving the correct per-message delays,
99 using a sophisticated preemptive message scheduling.
100
102 On an idle system, the queue manager waits for the arrival of trigger
103 events, or it waits for a timer to go off. A trigger is a one-byte mes‐
104 sage. Depending on the message received, the queue manager performs
105 one of the following actions (the message is followed by the symbolic
106 constant used internally by the software):
107 D (QMGR_REQ_SCAN_DEFERRED)
109 Start a deferred queue scan. If a deferred queue scan is
110 already in progress, that scan will be restarted as soon as it
111 finishes.
112 I (QMGR_REQ_SCAN_INCOMING)
114 Start an incoming queue scan. If an incoming queue scan is
115 already in progress, that scan will be restarted as soon as it
116 finishes.
117 A (QMGR_REQ_SCAN_ALL)
119 Ignore deferred queue file time stamps. The request affects the
120 next deferred queue scan.
121 F (QMGR_REQ_FLUSH_DEAD)
123 Purge all information about dead transports and destinations.
124 W (TRIGGER_REQ_WAKEUP)
126 Wakeup call, This is used by the master server to instantiate
127 servers that should not go away forever. The action is to start
128 an incoming queue scan.
129 The qmgr(8) daemon reads an entire buffer worth of triggers. Multiple
131 identical trigger requests are collapsed into one, and trigger requests
132 are sorted so that A and F precede D and I. Thus, in order to force a
133 deferred queue run, one would request A F D; in order to notify the
134 queue manager of the arrival of new mail one would request I.
135
137 RFC 3463 (Enhanced status codes)
138 RFC 3464 (Delivery status notifications)
139
141 The qmgr(8) daemon is not security sensitive. It reads single-character
142 messages from untrusted local users, and thus may be susceptible to
143 denial of service attacks. The qmgr(8) daemon does not talk to the out‐
144 side world, and it can be run at fixed low privilege in a chrooted
145 environment.
146
148 Problems and transactions are logged to the syslog daemon. Corrupted
149 message files are saved to the corrupt queue for further inspection.
150 Depending on the setting of the notify_classes parameter, the postmas‐
152 ter is notified of bounces and of other trouble.
153
155 A single queue manager process has to compete for disk access with mul‐
156 tiple front-end processes such as cleanup(8). A sudden burst of inbound
157 mail can negatively impact outbound delivery rates.
158
160 Changes to main.cf are not picked up automatically as qmgr(8) is a per‐
161 sistent process. Use the "postfix reload" command after a configuration
162 change.
163 The text below provides only a parameter summary. See postconf(5) for
165 more details including examples.
166 In the text below, transport is the first field in a master.cf entry.
168
170 allow_min_user (no)
171 Allow a recipient address to have `-' as the first character.
172
174 qmgr_clog_warn_time (300s)
175 The minimal delay between warnings that a specific destination
176 is clogging up the Postfix active queue.
177 qmgr_message_active_limit (20000)
179 The maximal number of messages in the active queue.
180 qmgr_message_recipient_limit (20000)
182 The maximal number of recipients held in memory by the Postfix
183 queue manager, and the maximal size of the size of the short-
184 term, in-memory "dead" destination status cache.
185 qmgr_message_recipient_minimum (10)
187 The minimal number of in-memory recipients for any message.
188 default_recipient_limit (20000)
190 The default per-transport upper limit on the number of in-memory
191 recipients.
192 transport_recipient_limit ($default_recipient_limit)
194 Idem, for delivery via the named message transport.
195 default_extra_recipient_limit (1000)
197 The default value for the extra per-transport limit imposed on
198 the number of in-memory recipients.
199 transport_extra_recipient_limit ($default_extra_recipient_limit)
201 Idem, for delivery via the named message transport.
202 Available in Postfix version 2.4 and later:
204 default_recipient_refill_limit (100)
206 The default per-transport limit on the number of recipients
207 refilled at once.
208 transport_recipient_refill_limit ($default_recipient_refill_limit)
210 Idem, for delivery via the named message transport.
211 default_recipient_refill_delay (5s)
213 The default per-transport maximum delay between recipients
214 refills.
215 transport_recipient_refill_delay ($default_recipient_refill_delay)
217 Idem, for delivery via the named message transport.
218
220 initial_destination_concurrency (5)
221 The initial per-destination concurrency level for parallel
222 delivery to the same destination.
223 default_destination_concurrency_limit (20)
225 The default maximal number of parallel deliveries to the same
226 destination.
227 transport_destination_concurrency_limit ($default_destination_concur‐
229 rency_limit)
230 Idem, for delivery via the named message transport.
231
233 default_destination_recipient_limit (50)
234 The default maximal number of recipients per message delivery.
235 transport_destination_recipient_limit ($default_destination_recipi‐
237 ent_limit)
238 Idem, for delivery via the named message transport.
239
241 default_delivery_slot_cost (5)
242 How often the Postfix queue manager's scheduler is allowed to
243 preempt delivery of one message with another.
244 transport_delivery_slot_cost ($default_delivery_slot_cost)
246 Idem, for delivery via the named message transport.
247 default_minimum_delivery_slots (3)
249 How many recipients a message must have in order to invoke the
250 Postfix queue manager's scheduling algorithm at all.
251 transport_minimum_delivery_slots ($default_minimum_delivery_slots)
253 Idem, for delivery via the named message transport.
254 default_delivery_slot_discount (50)
256 The default value for transport-specific _delivery_slot_discount
257 settings.
258 transport_delivery_slot_discount ($default_delivery_slot_discount)
260 Idem, for delivery via the named message transport.
261 default_delivery_slot_loan (3)
263 The default value for transport-specific _delivery_slot_loan
264 settings.
265 transport_delivery_slot_loan ($default_delivery_slot_loan)
267 Idem, for delivery via the named message transport.
268
270 minimal_backoff_time (version dependent)
271 The minimal time between attempts to deliver a deferred message.
272 maximal_backoff_time (4000s)
274 The maximal time between attempts to deliver a deferred message.
275 maximal_queue_lifetime (5d)
277 The maximal time a message is queued before it is sent back as
278 undeliverable.
279 queue_run_delay (version dependent)
281 The time between deferred queue scans by the queue manager.
282 transport_retry_time (60s)
284 The time between attempts by the Postfix queue manager to con‐
285 tact a malfunctioning message delivery transport.
286 Available in Postfix version 2.1 and later:
288 bounce_queue_lifetime (5d)
290 The maximal time a bounce message is queued before it is consid‐
291 ered undeliverable.
292
294 config_directory (see 'postconf -d' output)
295 The default location of the Postfix main.cf and master.cf con‐
296 figuration files.
297 daemon_timeout (18000s)
299 How much time a Postfix daemon process may take to handle a
300 request before it is terminated by a built-in watchdog timer.
301 defer_transports (empty)
303 The names of message delivery transports that should not deliver
304 mail unless someone issues "sendmail -q" or equivalent.
305 delay_logging_resolution_limit (2)
307 The maximal number of digits after the decimal point when log‐
308 ging sub-second delay values.
309 helpful_warnings (yes)
311 Log warnings about problematic configuration settings, and pro‐
312 vide helpful suggestions.
313 ipc_timeout (3600s)
315 The time limit for sending or receiving information over an
316 internal communication channel.
317 process_id (read-only)
319 The process ID of a Postfix command or daemon process.
320 process_name (read-only)
322 The process name of a Postfix command or daemon process.
323 queue_directory (see 'postconf -d' output)
325 The location of the Postfix top-level queue directory.
326 syslog_facility (mail)
328 The syslog facility of Postfix logging.
329 syslog_name (postfix)
331 The mail system name that is prepended to the process name in
332 syslog records, so that "smtpd" becomes, for example, "post‐
333 fix/smtpd".
334
336 /var/spool/postfix/incoming, incoming queue
337 /var/spool/postfix/active, active queue
338 /var/spool/postfix/deferred, deferred queue
339 /var/spool/postfix/bounce, non-delivery status
340 /var/spool/postfix/defer, non-delivery status
341 /var/spool/postfix/trace, delivery status
342
344 trivial-rewrite(8), address routing
345 bounce(8), delivery status reports
346 postconf(5), configuration parameters
347 master(5), generic daemon options
348 master(8), process manager
349 syslogd(8), system logging
350
352 Use "postconf readme_directory" or "postconf html_directory" to locate
353 this information.
354 SCHEDULER_README, scheduling algorithm
355 QSHAPE_README, Postfix queue analysis
356
358 The Secure Mailer license must be distributed with this software.
359
361 Wietse Venema
362 IBM T.J. Watson Research
363 P.O. Box 704
364 Yorktown Heights, NY 10598, USA
365 Scheduler enhancements:
367 Patrik Rak
368 Modra 6
369 155 00, Prague, Czech Republic
370 QMGR(8)