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<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN"
        "http://www.w3.org/TR/html4/loose.dtd">
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<title> Postfix manual - verify(8) </title>
</head> <body> <pre>
VERIFY(8)                                                            VERIFY(8)

<b>NAME</b>
       verify - Postfix address verification server

<b>SYNOPSIS</b>
       <b>verify</b> [generic Postfix daemon options]

<b>DESCRIPTION</b>
       The  <a href="verify.8.html"><b>verify</b>(8)</a>  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  <a href="verify.8.html"><b>verify</b>(8)</a>  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 <a href="verify.8.html"><b>verify</b>(8)</a> server implements the following requests:

       <b>update</b> <i>address status text</i>
              Update the status and text of the specified address.

       <b>query</b> <i>address</i>
              Look up the <i>status</i> and <i>text</i> for the specified <i>address</i>.   If  the
              status  is  unknown, a probe is sent and an "in progress" status
              is returned.

<b>SECURITY</b>
       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 <a href="verify.8.html"><b>verify</b>(8)</a> server no longer uses
       root privileges when opening the  <b><a href="postconf.5.html#address_verify_map">address_verify_map</a></b>  cache  file.  The
       file should now be stored under the Postfix-owned <b><a href="postconf.5.html#data_directory">data_directory</a></b>.  As a
       migration aid, an attempt to open a  cache  file  under  a  non-Postfix
       directory  is  redirected  to  the  Postfix-owned <b><a href="postconf.5.html#data_directory">data_directory</a></b>, and a
       warning is logged.

<b>DIAGNOSTICS</b>
       Problems and transactions are logged to <b>syslogd</b>(8).

<b>BUGS</b>
       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 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.

<b>CONFIGURATION PARAMETERS</b>
       Changes to <a href="postconf.5.html"><b>main.cf</b></a> are not picked up automatically, as  <a href="verify.8.html"><b>verify</b>(8)</a>  pro-
       cesses are long-lived. Use the command "<b>postfix reload</b>" after a config-
       uration change.

       The text below provides only a parameter summary. See  <a href="postconf.5.html"><b>postconf</b>(5)</a>  for
       more details including examples.

<b>PROBE MESSAGE CONTROLS</b>
       <b><a href="postconf.5.html#address_verify_sender">address_verify_sender</a> ($<a href="postconf.5.html#double_bounce_sender">double_bounce_sender</a>)</b>
              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:

       <b><a href="postconf.5.html#address_verify_sender_ttl">address_verify_sender_ttl</a> (0s)</b>
              The time  between  changes  in  the  time-dependent  portion  of
              address verification probe sender addresses.

<b>CACHE CONTROLS</b>
       <b><a href="postconf.5.html#address_verify_map">address_verify_map</a> (see 'postconf -d' output)</b>
              Lookup table for persistent address verification status storage.

       <b><a href="postconf.5.html#address_verify_positive_expire_time">address_verify_positive_expire_time</a> (31d)</b>
              The time after which a successful probe expires from the address
              verification cache.

       <b><a href="postconf.5.html#address_verify_positive_refresh_time">address_verify_positive_refresh_time</a> (7d)</b>
              The  time  after  which  a successful address verification probe
              needs to be refreshed.

       <b><a href="postconf.5.html#address_verify_negative_cache">address_verify_negative_cache</a> (yes)</b>
              Enable caching of failed address verification probe results.

       <b><a href="postconf.5.html#address_verify_negative_expire_time">address_verify_negative_expire_time</a> (3d)</b>
              The time after which a failed probe  expires  from  the  address
              verification cache.

       <b><a href="postconf.5.html#address_verify_negative_refresh_time">address_verify_negative_refresh_time</a> (3h)</b>
              The  time  after which a failed address verification probe needs
              to be refreshed.

       Available with Postfix 2.7 and later:

       <b><a href="postconf.5.html#address_verify_cache_cleanup_interval">address_verify_cache_cleanup_interval</a> (12h)</b>
              The amount of time between <a href="verify.8.html"><b>verify</b>(8)</a> address verification  data-
              base cleanup runs.

<b>PROBE MESSAGE ROUTING CONTROLS</b>
       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.

       <b><a href="postconf.5.html#address_verify_relayhost">address_verify_relayhost</a> ($<a href="postconf.5.html#relayhost">relayhost</a>)</b>
              Overrides  the <a href="postconf.5.html#relayhost">relayhost</a> parameter setting for address verifica-
              tion probes.

       <b><a href="postconf.5.html#address_verify_transport_maps">address_verify_transport_maps</a> ($<a href="postconf.5.html#transport_maps">transport_maps</a>)</b>
              Overrides the <a href="postconf.5.html#transport_maps">transport_maps</a> parameter setting for address veri-
              fication probes.

       <b><a href="postconf.5.html#address_verify_local_transport">address_verify_local_transport</a> ($<a href="postconf.5.html#local_transport">local_transport</a>)</b>
              Overrides the <a href="postconf.5.html#local_transport">local_transport</a> parameter setting for address ver-
              ification probes.

       <b><a href="postconf.5.html#address_verify_virtual_transport">address_verify_virtual_transport</a> ($<a href="postconf.5.html#virtual_transport">virtual_transport</a>)</b>
              Overrides the <a href="postconf.5.html#virtual_transport">virtual_transport</a> parameter  setting  for  address
              verification probes.

       <b><a href="postconf.5.html#address_verify_relay_transport">address_verify_relay_transport</a> ($<a href="postconf.5.html#relay_transport">relay_transport</a>)</b>
              Overrides the <a href="postconf.5.html#relay_transport">relay_transport</a> parameter setting for address ver-
              ification probes.

       <b><a href="postconf.5.html#address_verify_default_transport">address_verify_default_transport</a> ($<a href="postconf.5.html#default_transport">default_transport</a>)</b>
              Overrides the <a href="postconf.5.html#default_transport">default_transport</a> parameter  setting  for  address
              verification probes.

       Available in Postfix 2.3 and later:

       <b><a href="postconf.5.html#address_verify_sender_dependent_relayhost_maps">address_verify_sender_dependent_relayhost_maps</a>          ($<a href="postconf.5.html#sender_dependent_relayhost_maps">sender_depen</a>-</b>
       <b><a href="postconf.5.html#sender_dependent_relayhost_maps">dent_relayhost_maps</a>)</b>
              Overrides  the <a href="postconf.5.html#sender_dependent_relayhost_maps">sender_dependent_relayhost_maps</a> parameter setting
              for address verification probes.

       Available in Postfix 2.7 and later:

       <b><a href="postconf.5.html#address_verify_sender_dependent_default_transport_maps">address_verify_sender_dependent_default_transport_maps</a>  ($<a href="postconf.5.html#sender_dependent_default_transport_maps">sender_depen</a>-</b>
       <b><a href="postconf.5.html#sender_dependent_default_transport_maps">dent_default_transport_maps</a>)</b>
              Overrides the <a href="postconf.5.html#sender_dependent_default_transport_maps">sender_dependent_default_transport_maps</a>  parameter
              setting for address verification probes.

<b>MISCELLANEOUS CONTROLS</b>
       <b><a href="postconf.5.html#config_directory">config_directory</a> (see 'postconf -d' output)</b>
              The  default  location of the Postfix <a href="postconf.5.html">main.cf</a> and <a href="master.5.html">master.cf</a> con-
              figuration files.

       <b><a href="postconf.5.html#daemon_timeout">daemon_timeout</a> (18000s)</b>
              How much time a Postfix daemon process  may  take  to  handle  a
              request before it is terminated by a built-in watchdog timer.

       <b><a href="postconf.5.html#ipc_timeout">ipc_timeout</a> (3600s)</b>
              The  time  limit  for  sending  or receiving information over an
              internal communication channel.

       <b><a href="postconf.5.html#process_id">process_id</a> (read-only)</b>
              The process ID of a Postfix command or daemon process.

       <b><a href="postconf.5.html#process_name">process_name</a> (read-only)</b>
              The process name of a Postfix command or daemon process.

       <b><a href="postconf.5.html#queue_directory">queue_directory</a> (see 'postconf -d' output)</b>
              The location of the Postfix top-level queue directory.

       <b><a href="postconf.5.html#syslog_facility">syslog_facility</a> (mail)</b>
              The syslog facility of Postfix logging.

       <b><a href="postconf.5.html#syslog_name">syslog_name</a> (see 'postconf -d' output)</b>
              The mail system name that is prepended to the  process  name  in
              syslog  records,  so  that  "smtpd" becomes, for example, "post-
              fix/smtpd".

<b>SEE ALSO</b>
       <a href="smtpd.8.html">smtpd(8)</a>, Postfix SMTP server
       <a href="cleanup.8.html">cleanup(8)</a>, enqueue Postfix message
       <a href="postconf.5.html">postconf(5)</a>, configuration parameters
       syslogd(5), system logging

<b>README FILES</b>
       <a href="ADDRESS_VERIFICATION_README.html">ADDRESS_VERIFICATION_README</a>, address verification howto

<b>LICENSE</b>
       The Secure Mailer license must be distributed with this software.

<b>HISTORY</b>
       This service was introduced with Postfix version 2.1.

<b>AUTHOR(S)</b>
       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

                                                                     VERIFY(8)
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