VERIFY(8) System Manager's Manual VERIFY(8)

verify - Postfix address verification server

verify [generic Postfix daemon options]

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 the status and text of the specified 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.



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 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.










Problems and transactions are logged to syslogd(8).










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.










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 including examples.











  

  
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:



  

  
The time between changes in the time-dependent portion of address
      verification probe sender addresses.













  

  
Lookup table for persistent address verification status storage.

  

  
The time after which a successful probe expires from the address
      verification cache.

  

  
The time after which a successful address verification probe needs to be
      refreshed.

  

  
Enable caching of failed address verification probe results.

  

  
The time after which a failed probe expires from the address verification
      cache.

  

  
The time after which a failed address verification probe needs to be
      refreshed.




Available with Postfix 2.7 and later:



  

  
The amount of time between verify(8) address verification database
      cleanup runs.












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.



  

  
Overrides the relayhost parameter setting for address verification
    probes.

  

  
Overrides the transport_maps parameter setting for address verification
      probes.

  

  
Overrides the local_transport parameter setting for address verification
      probes.

  

  
Overrides the virtual_transport parameter setting for address verification
      probes.

  

  
Overrides the relay_transport parameter setting for address verification
      probes.

  

  
Overrides the default_transport parameter setting for address verification
      probes.




Available in Postfix 2.3 and later:



  

  
Overrides the sender_dependent_relayhost_maps parameter setting for
      address verification probes.




Available in Postfix 2.7 and later:



  

  
Overrides the sender_dependent_default_transport_maps parameter setting
      for address verification probes.












Preliminary SMTPUTF8 support is introduced with Postfix 3.0.



  

  
Detect that a message requires SMTPUTF8 support for the specified mail
      origin classes.




Available in Postfix version 3.2 and later:



  

  
Enable 'transitional' compatibility between IDNA2003 and IDNA2008, when
      converting UTF-8 domain names to/from the ASCII form that is used for DNS
      lookups.













  

  
The default location of the Postfix main.cf and master.cf configuration
      files.

  

  
How much time a Postfix daemon process may take to handle a request before
      it is terminated by a built-in watchdog timer.

  

  
The time limit for sending or receiving information over an internal
      communication channel.

  

  
The process ID of a Postfix command or daemon process.

  

  
The process name of a Postfix command or daemon process.

  

  
The location of the Postfix top-level queue directory.

  

  
The syslog facility of Postfix logging.

  

  
A prefix that is prepended to the process name in syslog records, so that,
      for example, "smtpd" becomes "prefix/smtpd".










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










Use "postconf readme_directory" or
    "postconf 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 2.1.








Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA