VERIFY(8)		    System Manager's Manual		     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 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)  pro-
       cesses are persistent. 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.

CACHE CONTROLS
       address_verify_map (empty)
	      Optional lookup table for persistent address verification 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 "postmaster".

       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.

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.

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)
	      The mail system name that is prepended to the  process  name  in
	      syslog  records,	so  that  "smtpd" becomes, for example, "post-
	      fix/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(8)