Duplicate message ids in the sendmail log

Here's a quick little perl script that can help you find duplicate message ids in your sendmail log. Script and explanation after the break.

#!perl

while (<>) {
        ($_ =~ /msgid=\<(.*?)\>?,/) && ($msgid = $1);
        $ids{$msgid}++;
        print $msgid . "\n" if ($ids{$msgid} == 2);
}

Where to use this script? Let's say, hypothetically, that you have email coming in that is causing the mail server to tempfail a message (over and over). Or you have a server that is sending a mail message over and over. This script can help you find those messages quickly.