You could, if you have access to the server that you host on, edit the aliases file (on unix) and point a email address to a perl file, use the perl file to read any values and arguments, and then use that to pass to PHP.
I thin this is a very basic outline of how it can be done, but I think that it is a possibility.
procmail is definatly the way to go if you have it. It's a very powerfull tool. I do just that looking for bounce messages. A mail comes in an a PHP script fires to process it. Then decide weither to pass it to me or delete it.
Sure ... anything a human on a browser can do can be replicated with some kind of scripting. Addressing the "or something else" rather than the PHP part of your question, the perl module Mail::POP3Client makes it a snap to write a perl script to check a pop3 account and automatically manipulate email to your hearts content. Set the script up to run automatically every few minutes/hours and it's makes for a nice way to handle various concerns of incoming email.