# verify(8) - man - phpMan [VERIFY(8postfix)](https://www.chedong.com/phpMan.php/man/VERIFY/8postfix/markdown) [VERIFY(8postfix)](https://www.chedong.com/phpMan.php/man/VERIFY/8postfix/markdown) ## NAME verify - Postfix address verification server ## SYNOPSIS **verify** [generic Postfix daemon options] ## DESCRIPTION The [**verify**(8)](https://www.chedong.com/phpMan.php/man/verify/8/markdown) 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 dis‐ carded 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)](https://www.chedong.com/phpMan.php/man/verify/8/markdown) server is designed to run under control by the Postfix master server. It main‐ tains 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)](https://www.chedong.com/phpMan.php/man/verify/8/markdown) 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 privi‐ lege. The address verification server can be coerced to store unlimited amounts of garbage. Limit‐ ing 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)](https://www.chedong.com/phpMan.php/man/verify/8/markdown) server no longer uses root privileges when opening the **address**___**verify**___**map** cache file. The file should now be stored under the Post‐ fix-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)](https://www.chedong.com/phpMan.php/man/syslogd/8/markdown) or [**postlogd**(8)](https://www.chedong.com/phpMan.php/man/postlogd/8/markdown). ## BUGS Address verification probe messages add additional traffic to the mail queue. Recipient ver‐ ification may cause an increased load on down-stream servers in the case of a dictionary at‐ tack or a flood of backscatter bounces. Sender address verification may cause your site to be denylisted by some providers. If the persistent database ever gets corrupted then the world comes to an end and human in‐ tervention is needed. This violates a basic Postfix principle. ## CONFIGURATION PARAMETERS Changes to **main.cf** are not picked up automatically, as [**verify**(8)](https://www.chedong.com/phpMan.php/man/verify/8/markdown) processes are long-lived. Use the command "**postfix** **reload**" after a configuration change. The text below provides only a parameter summary. See [**postconf**(5)](https://www.chedong.com/phpMan.php/man/postconf/5/markdown) for more details including examples. ## PROBE MESSAGE CONTROLS **address**___**verify**___**sender** **($double**___**bounce**___**sender)** The sender address to use in address verification probes; prior to Postfix 2.5 the de‐ fault was "postmaster". Available with Postfix 2.9 and later: **address**___**verify**___**sender**___**ttl** **(0s)** The time between changes in the time-dependent portion of address verification probe sender addresses. ## CACHE CONTROLS **address**___**verify**___**map** **(see** **'postconf** **-d'** **output)** Lookup table for persistent address verification status storage. **address**___**verify**___**positive**___**expire**___**time** **(31d)** The time after which a successful probe expires from the address verification cache. **address**___**verify**___**positive**___**refresh**___**time** **(7d)** The time after which a successful address verification probe needs to be refreshed. **address**___**verify**___**negative**___**cache** **(yes)** Enable caching of failed address verification probe results. **address**___**verify**___**negative**___**expire**___**time** **(3d)** The time after which a failed probe expires from the address verification cache. **address**___**verify**___**negative**___**refresh**___**time** **(3h)** The time after which a failed address verification probe needs to be refreshed. Available with Postfix 2.7 and later: **address**___**verify**___**cache**___**cleanup**___**interval** **(12h)** The amount of time between [**verify**(8)](https://www.chedong.com/phpMan.php/man/verify/8/markdown) address verification database cleanup runs. ## PROBE MESSAGE ROUTING CONTROLS By default, probe messages are delivered via the same route as regular messages. The follow‐ ing parameters can be used to override specific message routing mechanisms. **address**___**verify**___**relayhost** **($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** **($default**___**transport)** Overrides the default_transport parameter setting for address verification probes. Available in Postfix 2.3 and later: **address**___**verify**___**sender**___**dependent**___**relayhost**___**maps** **($sender**___**dependent**___**relayhost**___**maps)** Overrides the sender_dependent_relayhost_maps parameter setting for address verifica‐ tion probes. Available in Postfix 2.7 and later: **address**___**verify**___**sender**___**dependent**___**default**___**transport**___**maps** **($sender**___**dependent**___**default**___**trans**‐‐ **port**___**maps)** Overrides the sender_dependent_default_transport_maps parameter setting for address verification probes. ## SMTPUTF8 CONTROLS Preliminary SMTPUTF8 support is introduced with Postfix 3.0. **smtputf8**___**autodetect**___**classes** **(sendmail,** **verify)** Detect that a message requires SMTPUTF8 support for the specified mail origin classes. Available in Postfix version 3.2 and later: **enable**___**idna2003**___**compatibility** **(no)** Enable 'transitional' compatibility between IDNA2003 and IDNA2008, when converting UTF-8 domain names to/from the ASCII form that is used for DNS lookups. ## 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 ter‐ minated 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)** A prefix that is prepended to the process name in syslog records, so that, for exam‐ ple, "smtpd" becomes "prefix/smtpd". Available in Postfix 3.3 and later: **service**___**name** **(read-only)** The master.cf service name of a Postfix daemon process. ## SEE ALSO [smtpd(8)](https://www.chedong.com/phpMan.php/man/smtpd/8/markdown), Postfix SMTP server [cleanup(8)](https://www.chedong.com/phpMan.php/man/cleanup/8/markdown), enqueue Postfix message [postconf(5)](https://www.chedong.com/phpMan.php/man/postconf/5/markdown), configuration parameters [postlogd(8)](https://www.chedong.com/phpMan.php/man/postlogd/8/markdown), Postfix logging [syslogd(8)](https://www.chedong.com/phpMan.php/man/syslogd/8/markdown), 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 Wietse Venema Google, Inc. 111 8th Avenue New York, NY 10011, USA [VERIFY(8postfix)](https://www.chedong.com/phpMan.php/man/VERIFY/8postfix/markdown)