VERIFY(8postfix)                                                                 VERIFY(8postfix)



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  net‐
       work,  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. Lim‐
       iting  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).

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 dictio‐
       nary attack or a flood of backscatter bounces.  Sender address verification may cause your
       site to be blacklisted 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 includ‐
       ing 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 fol‐
       lowing 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 verifi‐
              cation probes.

       Available in Postfix 2.7 and later:

       address_verify_sender_dependent_default_transport_maps   ($sender_dependent_default_trans‐
       port_maps)
              Overrides the sender_dependent_default_transport_maps parameter setting for address
              verification probes.

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)
              The  mail  system  name that is prepended to the process name in syslog records, so
              that "smtpd" becomes, for example, "postfix/smtpd".

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

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



                                                                                 VERIFY(8postfix)