Provided by: postfix_3.6.4-1ubuntu2_amd64 bug


       verify - 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 undeliverable.

       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 group.

       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 expiry time 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


       Problems and transactions are logged to syslogd(8) or postlogd(8).


       Address verification probe messages add additional traffic to the mail  queue.   Recipient
       verification  may  cause  an  increased  load  on  down-stream  servers  in  the case of a
       dictionary attack or a flood of backscatter  bounces.   Sender  address  verification  may
       cause your site to be denylisted by some providers.

       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 are not picked up automatically, as verify(8) processes are long-lived.
       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_sender ($double_bounce_sender)
              The sender address to use in address verification probes; prior to Postfix 2.5  the
              default was "postmaster".

       Available with Postfix 2.9 and later:

       address_verify_sender_ttl (0s)
              The  time  between  changes  in  the time-dependent portion of address verification
              probe sender addresses.


       address_verify_map (see 'postconf -d' output)
              Lookup table for persistent address verification status storage.

       address_verify_positive_expire_time (31d)
              The time after which a successful  probe  expires  from  the  address  verification

       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 verification cache.

       address_verify_negative_refresh_time (3h)
              The time after which a failed address verification probe needs to be refreshed.

       Available with Postfix 2.7 and later:

       address_verify_cache_cleanup_interval (12h)
              The amount of time between verify(8) address verification database cleanup runs.


       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 probes.

       address_verify_transport_maps ($transport_maps)
              Overrides the transport_maps parameter setting for address verification probes.

       address_verify_local_transport ($local_transport)
              Overrides the local_transport parameter setting for address verification probes.

       address_verify_virtual_transport ($virtual_transport)
              Overrides the virtual_transport parameter setting for address verification probes.

       address_verify_relay_transport ($relay_transport)
              Overrides the relay_transport parameter setting for address verification probes.

       address_verify_default_transport ($default_transport)
              Overrides the default_transport parameter setting for address verification probes.

       Available in Postfix 2.3 and later:

       address_verify_sender_dependent_relayhost_maps ($sender_dependent_relayhost_maps)
              Overrides  the  sender_dependent_relayhost_maps  parameter  setting   for   address
              verification probes.

       Available in Postfix 2.7 and later:

              Overrides the sender_dependent_default_transport_maps parameter setting for address
              verification probes.


       Preliminary SMTPUTF8 support is introduced with Postfix 3.0.

       smtputf8_autodetect_classes (sendmail, verify)
              Detect  that  a  message  requires  SMTPUTF8  support for the specified mail origin

       Available in Postfix version 3.2 and later:

       enable_idna2003_compatibility (no)
              Enable 'transitional' compatibility between IDNA2003 and IDNA2008, when  converting
              UTF-8 domain names to/from the ASCII form that is used for DNS lookups.


       config_directory (see 'postconf -d' output)
              The default location of the Postfix and configuration files.

       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  communication

       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 3.3 and later:

       service_name (read-only)
              The service name of a Postfix daemon process.


       smtpd(8), Postfix SMTP server
       cleanup(8), enqueue Postfix message
       postconf(5), configuration parameters
       postlogd(8), Postfix logging
       syslogd(8), 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.


       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA