Postfix manual - verify(8)

    VERIFY(8)                                                            VERIFY(8)

    NAME
           verify - Postfix address verification server

    SYNOPSIS
           verify [generic Postfix daemon options]

    DESCRIPTION
           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.

    SECURITY
           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 logged.

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

    BUGS
           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.

    CONFIGURATION PARAMETERS
           Changes to main.cf are not picked up automatically, as  verify(8)  pro-
           cesses are long-lived. Use the command "postfix reload" after a config-
           uration change.

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

    PROBE MESSAGE CONTROLS
           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.

    CACHE CONTROLS
           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  data-
                  base cleanup runs.

    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 verifica-
                  tion probes.

           address_verify_transport_maps ($transport_maps)
                  Overrides the transport_maps parameter setting for address veri-
                  fication probes.

           address_verify_local_transport ($local_transport)
                  Overrides the local_transport parameter setting for address ver-
                  ification 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 ver-
                  ification 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_depen-
           dent_relayhost_maps)
                  Overrides  the sender_dependent_relayhost_maps parameter setting
                  for address verification probes.

           Available in Postfix 2.7 and later:

           address_verify_sender_dependent_default_transport_maps  ($sender_depen-
           dent_default_transport_maps)
                  Overrides the sender_dependent_default_transport_maps  parameter
                  setting for address verification probes.

    SMTPUTF8 CONTROLS
           Preliminary SMTPUTF8 support is introduced with Postfix 3.0.

           smtputf8_autodetect_classes (sendmail, verify)
                  Detect  that  a message requires SMTPUTF8 support for the speci-
                  fied 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.

    MISCELLANEOUS CONTROLS
           config_directory (see 'postconf -d' output)
                  The default location of the Postfix main.cf and  master.cf  con-
                  figuration 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.

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

    README FILES
           ADDRESS_VERIFICATION_README, address verification howto

    LICENSE
           The Secure Mailer license must be distributed with this software.

    HISTORY
           This service was introduced with Postfix version 2.1.

    AUTHOR(S)
           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

                                                                         VERIFY(8)