POP-Before-SMTP-Auth is a POP before SMTP daemon for Dovecot and Postfix that works by scanning mail server log files. The line-matching regex can be changed from the configuration file, in case Dovecot's logging format changes, and also to adapt the script for use with something besides Dovecot. Presently the script requires that the IP address appear on a single line with the successful login in the log file.
