verify - Postfix address verification server
verify [generic Postfix daemon options]
(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.
(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.
(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.
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
Problems and transactions are logged to syslogd
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
processes are long-lived. Use the command " postfix reload
after a configuration change.
The text below provides only a parameter summary. See postconf
more details including examples.
- address_verify_sender ($double_bounce_sender)
- The sender address to use in address verification probes;
prior to Postfix 2.5 the default was "postmaster".
Available with Postfix 2.9 and later:
- address_verify_sender_ttl (0s)
- The time between changes in the time-dependent portion of
address verification probe sender addresses.
- address_verify_map (see 'postconf -d' output)
- Lookup table for persistent address verification status
- address_verify_positive_expire_time (31d)
- The time after which a successful probe expires from the
address verification cache.
- address_verify_positive_refresh_time (7d)
- The time after which a successful address verification
probe needs to be refreshed.
- address_verify_negative_cache (yes)
- Enable caching of failed address verification probe
- address_verify_negative_expire_time (3d)
- The time after which a failed probe expires from the
address verification cache.
- address_verify_negative_refresh_time (3h)
- The time after which a failed address verification probe
needs to be refreshed.
Available with Postfix 2.7 and later:
- address_verify_cache_cleanup_interval (12h)
- The amount of time between verify(8) address
verification database cleanup runs.
By default, probe messages are delivered via the same route as regular messages.
The following parameters can be used to override specific message routing
- address_verify_relayhost ($relayhost)
- Overrides the relayhost parameter setting for address
- address_verify_transport_maps ($transport_maps)
- Overrides the transport_maps parameter setting for address
- Overrides the local_transport parameter setting for address
- Overrides the virtual_transport parameter setting for
address verification probes.
- Overrides the relay_transport parameter setting for address
- 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.
- 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.
- config_directory (see 'postconf -d' output)
- The default location of the Postfix main.cf and master.cf
- 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
- 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
smtpd(8), Postfix SMTP server
cleanup(8), enqueue Postfix message
postconf(5), configuration parameters
syslogd(5), system logging
Use " postconf readme_directory
" or " postconf
" 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.
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
111 8th Avenue
New York, NY 10011, USA