Ubuntu Manpage: policyd-spf - pure-Python Postfix policy daemon for SPF checking

Provided by: postfix-policyd-spf-python_2.9.2-1_all

NAME

       policyd-spf - pure-Python Postfix policy daemon for SPF checking

VERSION

       2.0.0

USAGE

       NOTE: Depending on the packaging and distribution, the exact path to the executable may
       vary.

       $ policyd-spf (Start using installed config file)

       $ policyd-spf -h (Display usage message)

       $ policyd-spf /etc/postfix-policyd-spf-python/policyd-spf.conf
         (Config file name to use)

       Configuration options are described in the sample configuration file installed in
       /usr/share/doc/postfix-policyd-spf-python (policyd-spf.conf.commented) and in policyd-
       spf.conf(5).  The provided setup.py installs an uncommented configuration file in
       /etc/postfix-policyd-spf-python/.

       Additionally, whitelisting certain IP addresses or IP addresses used by listed domains
       from SPF checks is supported.  Skipping SPF checks for local submission or trusted relays
       is also provided.  The sample configuration file and policyd-spf.conf(5) shows the format
       to use.

SYNOPSIS

       python-policyd-spf is a Postfix SMTPd policy daemon for SPF checking.  It is implemented
       in pure Python and uses the pyspf module.  The SPF web site is http://www.openspf.org/.
       The Postfix configuration must be changed to check SPF.

DESCRIPTION

Logging is sent to syslogd.

Each time a Postfix SMTP server process is started it connects to the policy service
socket and Postfix runs one instance of this Python script. By default, a Postfix SMTP
server process terminates after 100 seconds of idle time, or after serving 100 clients.
Thus, the cost of starting this Python script is smoothed over time

The default policy_time_limit is 1000 seconds. This may be too short for some SMTP
transactions to complete. As recommended in SMTPD_POLICY_README, this should be extended
to 3600 seconds. To do so, set "policy_time_limit = 3600" in /etc/postfix/main.cf.

Messages that get a Fail SPF result will be rejected. Messages that get a Permerror are,
by default, treated as if they had no SPF record. Messages that get a Temperror result
are, by default, treated as if they had no SPF record, but can (and probably should) be
deferred if otherwise permitted. Messages that get other SPF results (Pass, None,
Neutral, Softfail) will have the SPF Received header prepended. Note: Spamasassisn 3.2
and follow will use this header for spam scoring so there is no need to configure a
separate SPF check in these Spamassassin versions. See Spamassassin documentation for
details.

Default Mail From rejection/deferal criteria are, by design, conservative. Default HELO
check actions are to reject mail with other than Pass/None. HELO records are much simpler
than Mail From records and rejecting based on HELO checking does not present a false
positive risk. These settings are a matter of local policy and should be adjusted to meet
the requirements of site administrators. See policyd-spf.conf(5) for configuration file
details.

LOGGING

       Policyd-spf will log messages to syslog about it's activities.  The "debugLevel" value in
       "policyd-spf.conf" can be increased to get additional information to be logged.  When set
       to a value of "0", only test results (SPF hits/misses) are logged.  Results will be
       returned to Postfix and logged as a warning by Postfix also.  For logging by this policy
       server, look for "policyd-spf" in your mail log files.

TESTING THE POLICY DAEMON

       Testing the policy daemon

       To test the policy daemon by hand, execute:

           policyd-spf

       Each query is a bunch of attributes.  Order does not matter, and the daemon uses only a
       few of all the attributes shown below:

           request=smtpd_access_policy
           protocol_state=RCPT
           protocol_name=SMTP
           helo_name=some.domain.tld
           queue_id=8045F2AB23
           instance=12345.6789
           sender=foo@bar.tld
           recipient=bar@foo.tld
           client_address=1.2.3.4
           client_name=another.domain.tld
           [empty line]

       The policy daemon will answer in the same style, with an attribute list followed by a
       empty line:

           action=dunno
           [empty line]

POSTFIX INTEGRATION

        1. Add the following to /etc/postfix/master.cf:

               policyd-spf  unix  -       n       n       -       0       spawn
                   user=policyd-spf argv=/usr/bin/policyd-spf

           NOTE: Check the path to both the installed Python interpreter and
                 policyd-spf.  These vary from system to system.  To use non-default
                 settings, you must also add the config file (see above and
                 policyd-spf.conf(5) for details).  Python and Python 3 versions
                 prior to 3.3 are not supported.

        2. Configure the Postfix policy service in /etc/postfix/main.cf:

               smtpd_recipient_restrictions =
                   ...
                   reject_unauth_destination
                   check_policy_service unix:private/policyd-spf
                   ...
               policyd-spf_time_limit = 3600

           NOTE:  Specify check_policy_service AFTER reject_unauth_destination or
                  else your system can become an open relay.

        3. Reload Postfix.

PERFORMANCE CONSIDERATIONS

The time to complete DNS lookups associated with SPF checks is the most significant factor
in policy server performance. Use of a capable local caching resolver is highly
recommended. Specifics of resolver setup are outside the scope of this document.

Long waits for DNS answers can cause performance bottlenecks. There are two primary
controls, policyd-spf.conf(5) has details, provided to affect DNS timing. Lookup_Time
controls the overall time, in seconds, allowed for an SPF check to complete.
Whitelist_Lookup_Time controls the amount of time allowed for individual DNS lookups
associated with name based whitelist options.

Lookup_Time defaults to the 20 second value recommended by RFC 7208. This is a
conservative recommendation and often a lower limit works quite well. Delays associated
with whitelisting related DNS lookups can be avoided by using IP based options instead.

A shorter time increases the likelihood that the result for some messages will be a
temporary error rather then the actual correct result. To avoid some reported
interoperability issues with some greylisting implementations, TempError_Defer defaults to
False. With TempError_Defer set to True, such TempError messages will be deferred and
when retried, the responses should be in the local DNS resolver's cache.

The combination of a low Lookup_Time setting, TempError_Defer = True, and no DNS name
based whitelisting will maximize SPF checking throughput with only mimimal delays.
Consider a value of Lookup_Time = 5 seconds and monitor the system mail logs. If
TempError results are rare or non-existent, the value can be lowered. If such result are
common (more than 1% of mail), then the value should be raised.

AUTHORS

       This version of policyd-spf (python) was written by Copyright © 2007-2016 Scott Kitterman
       <scott@kitterman.com>.  It is derived from Tumgreyspf, written by Sean Reifschneider,
       tummy.com, ltd <jafo@tummy.com>. Portions of the documentation were written by Meng Weng
       Wong <mengwong@pobox.com>.

       This man-page was created by Scott Kitterman <scott@kitterman.com>.  It is licensed under
       the same terms as the program.

                                                                                   POLICYD-SPF(1)