Ubuntu Manpage: verify - Postfix address verification server

Provided by: postfix_3.10.2-1ubuntu1_amd64

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) 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.

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 database 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 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:

address_verify_sender_dependent_default_transport_maps ($sender_dependent_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 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.

MISCELLANEOUS CONTROLS

       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.

README FILES

       Use "postconf readme_directory" or "postconf html_directory" to locate this information.
       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)