VERIFY(8) 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 deliv-
erable 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 per-
sistent 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 directory is redirected to the Postfix-owned
data_directory, and a warning is logged.
DIAGNOSTICS
Problems and transactions are logged to syslogd(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
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.
CONFIGURATION PARAMETERS
Changes to main.cf are not picked up automatically, as
verify(8) processes are long-lived. Use the command "post-
fix reload" after a configuration change.
The text below provides only a parameter summary. See
postconf(5) for more details including examples.
CACHE CONTROLS
address_verify_map (see 'postconf -d' output)
Lookup table for persistent address verification
status storage.
address_verify_sender ($double_bounce_sender)
The sender address to use in address verification
probes; prior to Postfix 2.5 the default was "post-
master".
address_verify_positive_expire_time (31d)
The time after which a successful probe expires
from the address verification cache.
address_verify_positive_refresh_time (7d)
The time after which a successful address verifica-
tion probe needs to be refreshed.
address_verify_negative_cache (yes)
Enable caching of failed address verification probe
results.
address_verify_negative_expire_time (3d)
The time after which a failed probe expires from
the address verification cache.
address_verify_negative_refresh_time (3h)
The time after which a failed address verification
probe needs to be refreshed.
Available with Postfix 2.7 and later:
address_verify_cache_cleanup_interval (12h)
The amount of time between verify(8) address veri-
fication database cleanup runs.
PROBE MESSAGE ROUTING CONTROLS
By default, probe messages are delivered via the same
route as regular messages. The following parameters can
be used to override specific message routing mechanisms.
address_verify_relayhost ($relayhost)
Overrides the relayhost parameter setting for
address 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 verification probes.
Available in Postfix 2.7 and later:
address_verify_sender_dependent_default_transport_maps
($sender_dependent_default_transport_maps)
Overrides the sender_dependent_default_trans-
port_maps parameter setting for address verifica-
tion probes.
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 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
process.
queue_directory (see 'postconf -d' output)
The location of the Postfix top-level queue direc-
tory.
syslog_facility (mail)
The syslog facility of Postfix logging.
syslog_name (see 'postconf -d' output)
The mail system name that is prepended to the
process name in syslog records, so that "smtpd"
becomes, for example, "postfix/smtpd".
SEE ALSO
smtpd(8), Postfix SMTP server
cleanup(8), enqueue Postfix message
postconf(5), configuration parameters
syslogd(5), system logging
README FILES
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
VERIFY(8)