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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 ma- chinery 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 ad- dresses. 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 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 di- rectory is redirected to the Postfix-owned data_directory, and a warn- ing is logged. DIAGNOSTICS Problems and transactions are logged to syslogd(8) or postlogd(8). BUGS 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 denylisted 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. CONFIGURATION PARAMETERS Changes to main.cf are not picked up automatically, as verify(8) processes are long-lived. Use the command "postfix reload" after a con- figuration change. The text below provides only a parameter summary. See postconf(5) for more details including examples. PROBE MESSAGE CONTROLS address_verify_sender ($double_bounce_sender) The sender address to use in address verification probes; prior to Postfix 2.5 the default was "postmaster". Available with Postfix 2.9 and later: address_verify_sender_ttl (0s) The time between changes in the time-dependent portion of ad- dress verification probe sender addresses. CACHE CONTROLS address_verify_map (see 'postconf -d' output) Lookup table for persistent address verification status storage. address_verify_positive_expire_time (31d) The time after which a successful probe expires from the address verification cache. address_verify_positive_refresh_time (7d) The time after which a successful address verification probe needs to be refreshed. address_verify_negative_cache (yes) Enable caching of failed address verification probe results. address_verify_negative_expire_time (3d) The time after which a failed probe expires from the address verification cache. address_verify_negative_refresh_time (3h) The time after which a failed address verification probe needs to be refreshed. Available with Postfix 2.7 and later: address_verify_cache_cleanup_interval (12h) The amount of time between verify(8) address verification data- base cleanup runs. PROBE MESSAGE ROUTING CONTROLS By default, probe messages are delivered via the same route as regular messages. The following parameters can be used to override specific message routing mechanisms. address_verify_relayhost ($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 ($default_transport) Overrides the default_transport parameter setting for address verification probes. Available in Postfix 2.3 and later: address_verify_sender_dependent_relayhost_maps ($sender_dependent_re- layhost_maps) Overrides the sender_dependent_relayhost_maps parameter setting for address verification probes. Available in Postfix 2.7 and later: address_verify_sender_dependent_default_transport_maps ($sender_depen- dent_default_transport_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 speci- fied 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 con- figuration files. daemon_timeout (18000s) How much time a Postfix daemon process may take to handle a re- quest before it is terminated by a built-in watchdog timer. ipc_timeout (3600s) The time limit for sending or receiving information over an in- ternal 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 example, "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), Postfix SMTP server cleanup(8), enqueue Postfix message postconf(5), configuration parameters postlogd(8), Postfix logging syslogd(8), 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(8)
NAME | SYNOPSIS | DESCRIPTION | SECURITY | DIAGNOSTICS | BUGS | CONFIGURATION PARAMETERS | PROBE MESSAGE CONTROLS | CACHE CONTROLS | PROBE MESSAGE ROUTING CONTROLS | SMTPUTF8 CONTROLS | MISCELLANEOUS CONTROLS | SEE ALSO | README FILES | LICENSE | HISTORY | AUTHOR(S)
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