While not a perl solution, how about using a linux box and using tcpdump? Or a real packet analyzer? There are free ones available on the net.
in reply to Network Reliability Testing, problems with buffered sockets?
As a complete stab in the dark, I have run across something like this ages ago, turned out to be an email message that kept getting bounced back and forth between two email servers, each adding a "he's on vacation" message to the end. We found it about 3 days after it had started, and it was gigantic.