Section: Maintenance Commands (8)Index
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Postfix address verification server
verify [generic Postfix daemon options]
The verify(8) address verification server maintains a record
of what recipient addresses are known to be deliverable or
Addresses are verified by injecting probe messages into the
Postfix queue. Probe messages are run through all the routing
and rewriting machinery except for final delivery, and are
discarded rather than being deferred or bounced.
Address verification relies on the answer from the nearest
MTA for the specified address, and will therefore not detect
all undeliverable addresses.
The verify(8) server is designed to run under control
by the Postfix
master server. It maintains an optional persistent database.
To avoid being interrupted by "postfix stop" in the middle
of a database update, the process runs in a separate process
The verify(8) server implements the following requests:
- update address status text
Update the status and text of the specified address.
- query address
Look up the status and text for the specified address.
If the status is unknown, a probe is sent and an "in progress"
status is returned.
The address verification server is not security-sensitive. It does
not talk to the network, and it does not talk to local users.
The verify server can run chrooted at fixed low privilege.
The address verification server can be coerced to store
unlimited amounts of garbage. Limiting the cache size
trades one problem (disk space exhaustion) for another
one (poor response time to client requests).
With Postfix version 2.5 and later, the verify(8)
server no longer uses root privileges when opening the
address_verify_map cache file. The file should now
be stored under the Postfix-owned data_directory. As
a migration aid, an attempt to open a cache file under a
non-Postfix directory is redirected to the Postfix-owned
data_directory, and a warning is logged.
Problems and transactions are logged to syslogd(8).
The address verification service is suitable only for sites that
handle a low mail volume. Verification probes add additional
traffic to the mail queue and perform poorly under high load.
Servers may blacklist sites that probe excessively, or that
probe excessively for non-existent recipient addresses.
If the persistent database ever gets corrupted then the world
comes to an end and human intervention is needed. This violates
a basic Postfix principle.
Changes to main.cf are not picked up automatically,
processes are persistent. Use the command "postfix reload" after
a configuration change.
The text below provides only a parameter summary. See
postconf(5) for more details including examples.
- address_verify_map (empty)
Optional lookup table for persistent address verification status
- address_verify_sender ($double_bounce_sender)
The sender address to use in address verification probes; prior
to Postfix 2.5 the default was "postmaster".
- address_verify_positive_expire_time (31d)
The time after which a successful probe expires from the address
- address_verify_positive_refresh_time (7d)
The time after which a successful address verification probe needs
to be refreshed.
- address_verify_negative_cache (yes)
Enable caching of failed address verification probe results.
- address_verify_negative_expire_time (3d)
The time after which a failed probe expires from the address
- address_verify_negative_refresh_time (3h)
The time after which a failed address verification probe needs to
PROBE MESSAGE ROUTING CONTROLS
By default, probe messages are delivered via the same route
as regular messages. The following parameters can be used to
override specific message routing mechanisms.
- address_verify_relayhost ($relayhost)
Overrides the relayhost parameter setting for address verification
- address_verify_transport_maps ($transport_maps)
Overrides the transport_maps parameter setting for address verification
- address_verify_local_transport ($local_transport)
Overrides the local_transport parameter setting for address
- address_verify_virtual_transport ($virtual_transport)
Overrides the virtual_transport parameter setting for address
- address_verify_relay_transport ($relay_transport)
Overrides the relay_transport parameter setting for address
- address_verify_default_transport ($default_transport)
Overrides the default_transport parameter setting for address
- config_directory (see ‘postconf -d’ output)
The default location of the Postfix main.cf and master.cf
- daemon_timeout (18000s)
How much time a Postfix daemon process may take to handle a
request before it is terminated by a built-in watchdog timer.
- ipc_timeout (3600s)
The time limit for sending or receiving information over an internal
- 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)
The mail system name that is prepended to the process name in syslog
records, so that "smtpd" becomes, for example, "postfix/smtpd".
smtpd(8), Postfix SMTP server
cleanup(8), enqueue Postfix message
postconf(5), configuration parameters
syslogd(5), system logging
Use "postconf readme_directory" or
"postconf html_directory" to locate this information.
ADDRESS_VERIFICATION_README, address verification howto
The Secure Mailer license must be distributed with this software.
This service was introduced with Postfix version 2.1.
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
- CONFIGURATION PARAMETERS
- CACHE CONTROLS
- PROBE MESSAGE ROUTING CONTROLS
- MISCELLANEOUS CONTROLS
- SEE ALSO
- README FILES