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VERIFY(8)                                                            VERIFY(8)

       verify(1,8) - Postfix address verification server

       verify(1,8) [generic Postfix daemon options]

       The  verify(1,8)(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(1,8)(8)  server  is designed to run under control by the Postfix
       master(5,8) server. It maintains an optional persistent database.  To  avoid
       being interrupted by "postfix stop" in(1,8) the middle of a database update(7,n),
       the process runs in(1,8) a separate process group.

       The verify(1,8)(8) server implements the following requests:

       update(7,n) 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(1,8) 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(1,8)
       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(1,2,n)  to  client

       Problems and transactions are logged to syslogd(8).

       The address verification service is suitable only for sites that handle
       a low mail(1,8) volume. Verification probes add additional  traffic  to  the
       mail(1,8)  queue(1,3)  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(3,n) corrupted then the world comes to
       an end and human intervention is needed. This violates a basic  Postfix

       Changes  to are not picked up automatically, as verify(1,8)(8) pro-
       cesses are persistent. Use the command "postfix reload" after a config-
       uration change.

       The  text  below provides only a parameter summary. See postconf(1,5)(5) for
       more details including examples.

       address_verify_map (empty)
              Optional lookup table for persistent address verification status

       address_verify_sender (postmaster)
              The sender address to use in(1,8) address verification probes.

       address_verify_positive_expire_time (31d)
              The time(1,2,n) after which a successful probe expires from the address
              verification cache.

       address_verify_positive_refresh_time (7d)
              The time(1,2,n) 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(1,2,n)  after  which  a failed probe expires from the address
              verification cache.

       address_verify_negative_refresh_time (3h)
              The time(1,2,n) after which a failed address verification  probe  needs
              to be refreshed.

       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.

       config_directory (see 'postconf(1,5) -d' output)
              The  default  location of the Postfix and con-
              figuration files.

       daemon_timeout (18000s)
              How much time(1,2,n) a Postfix daemon process  may  take  to  handle  a
              request before it is terminated by a built-in watchdog(5,8) timer.

       ipc_timeout (3600s)
              The  time(1,2,n)  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(1,5) -d' output)
              The location of the Postfix top-level queue(1,3) directory.

       syslog_facility (mail(1,8))
              The syslog(2,3,5,3 Sys::Syslog) facility of Postfix logging.

       syslog_name (postfix)
              The mail(1,8) system name that is prepended to the  process  name  in(1,8)
              syslog(2,3,5,3 Sys::Syslog)  records,  so  that  "smtpd" becomes, for example, "post-

       smtpd(8), Postfix SMTP server
       cleanup(8), enqueue Postfix message
       postconf(1,5)(5), configuration parameters
       syslogd(5), system logging

       Use "postconf(1,5) readme_directory" or "postconf(1,5) 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(1,3,5) 2.1.

       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA


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