This script, by Viktor Dukhovni, untangles a Postfix logfile and groups the records one "session" at a time based on queue ID and process ID information. From auxiliary/collate/collate.pl.

Records from different sessions are separated by an empty line. Such text is easy to process with $/="" in perl, or RS="" in awk.

Usage: postfix-collate file...

It reads standard input when no file is specified.