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  deliv-
           erable 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 per-
           sistent 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 size
           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
           The  address  verification  service  is  suitable only for
           sites that handle a low mail volume.  Verification  probes
           add  additional  traffic  to  the  mail  queue and perform
           poorly under high load.  Servers may blacklist sites  that
           probe excessively, or that probe excessively for non-exis-
           tent recipient addresses.

           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 persistent. Use the command "post-
           fix reload" after a configuration change.

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

    CACHE CONTROLS
           address_verify_map (empty)
                  Optional  lookup table for persistent address veri-
                  fication status storage.

           address_verify_sender ($double_bounce_sender)
                  The sender address to use in  address  verification
                  probes; prior to Postfix 2.5 the default was "post-
                  master".

           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 verifica-
                  tion 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.

    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.

    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 direc-
                  tory.

           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
           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(8)