Updated: 2022/Sep/29

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VERIFY(8)                   System Manager's Manual                  VERIFY(8)

       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

       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

       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) 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

       Changes to main.cf 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 cache.

       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:

              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 classes.

       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 main.cf and master.cf
              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 channel.

       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 master.cf 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