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pop-before-smtp - watch log for POP/IMAP auth, update map allowing SMTP


 nohup pop-before-smtp [--config=FILE] [--[no]write] [--[no]debug] \
     [--[no]flock] [--reprocess] [--watchlog=FILE] [--dbfile=FILE] \
     [--logto=FILE] [--grace=SECONDS] [--daemon=PIDFILE] \
     [--version] [--dumpconfig] [--list]


pop-before-smtp watches your mail log file (e.g. /var/log/maillog) for lines written by your POP/IMAP software (e.g. UW popd/imapd) that indicate a successful login. When found, pop-before-smtp installs an entry for the IP in an on-disk hash (DB) that is watched by your SMTP software (e.g. Postfix, sendmail, qmail, etc.). It then expires these entries when 30 minutes have elapsed after the last POP/IMAP access from that IP.


Specify the config file to read instead of /etc/ Useful for testing a new configuration before you install it. This option must occur first on the command-line since it will be processed before reading the config file, and all other options will be processed after reading the config file.

Specify --nowrite if you don't want the DB file to be even opened, let alone updated. Useful for trying out pattern-matching rules, especially when used with --debug and --reprocess. (If your maillog is world-readable, you can even run the test as a non-privileged user.)

If you specify --debug, logging to stdout will be enabled, plus extra debug messages will be generated to help you diagnose local/remote IP distinctions. Specify --logto after this option if you want the messages to go somewhere other than stdout. Often combined with --reprocess.

Using --noflock will turn off the default file-locking used on the DB file.

Parse the whole maillog file, pretending that each line is happening again. Useful for testing, especially when combined with --debug and possibly --nowrite.

You can specify what maillog to watch for POP/IMAP events. The default in the script is /var/log/maillog, but the provided config file searches for an existing log file, also checking for /var/log/mail/info, /var/log/mail.log, /var/log/messages, or /var/adm/messages. Run ``pop-before-smtp --dumpconfig'' to see the actual value for your system.

You can specify what DB file to update. To see what the default value is for your system, run ``pop-before-smtp --dumpconfig''. Typically, the filename that is created/updated is this name with a ``.db'' suffix added (because the default tie function appends the ``.db'' onto the specified db name -- if you supply a custom tie function, it is free to choose to do something else).

Turns on logging to the specified file (use ``-'' for stdout).

Set the number of seconds that an IP address is authorized after it successfully signs in via POP or IMAP.

Output the current version of the script and exit. May be combined with --dumpconfig and --list in the same run.

Output some config info and exit. This makes it easy to see what things like the dbfile, logto, and watchlog values are being set to in the config file. May be combined with --version and --list in the same run.

List the current IPs contained in the DB file (if any) and exit. May be combined with --version and --dumpconfig in the same run.

Become a daemon by forking, redirecting STDIN/STDOUT/STDERR to /dev/null, calling setsid, calling chdir('/'), and writing out the process ID of the forked process into the specified PIDFILE.


This daemon directly requires four modules from CPAN, which are not included in the base Perl release as of this writing. See the quickstart guide for more information (either look at the README.QUICKSTART file in the source or visit

You should edit the supplied file to customize things for your local system, such as scanning for the right POP/IMAP authorization, setting various options, etc. Again, the quickstart guide cover this.

When starting up, pop-before-smtp builds an internal table of all netblocks natively permitted by your SMTP software (for Postfix it looks at the output of ``postconf mynetworks''). This allows us to filter out local IP addresses that are already authorized and thus need no special help from us.

This daemon likes a couple of helpers. Several init scripts are included with the source and a version customized for your current OS may have been installed in the same package as the pop-before-smtp script.

Once pop-before-smtp has been started (and thus the database file has been created), you'll need to modify your MTA's configuration to read the IPs from the database file. This is also covered in the quickstart guide.


See the website for the latest version. See the mailing list (referenced on the website) for support.


pop-before-smtp keeps two data structures for all currently-allowed hosts: a queue, and a hash. The queue contains [ipaddr, time] records, while the hash contains ipaddr => time. Every time the daemon wakes up to deal with something else from the logfile handle, it peeks a the front of the queue, and when the timestamp of the record there has expired (is > 30 minutes old) it tosses it, and if the timestamp in the hash equals the timestamp in the queue, it deletes the hash entry and the on-disk db file entry.

pop-before-smtp protects the writes to the db file by flock. As far as I know, the consequences of a collision (corrupt read in an smtpd) are relatively mild, and the likelihood of one is remote, but the performance impact of the locking seems to be negligible, so it's enabled by default. To disable the flocking, invoke with --noflock or set ``$flock = 0'' in the config file.


Pop-before-smtp was created by Bennett Todd <>. It is currently being maintained by Wayne Davison <>.

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