I've got some experience here, so let me throw out a few observations in addition to what everyone else has said.

• You can create a "close" soloution to your problem pretty easily, but the "perfect" soloution is a lot of work. For example, you're right that bounces tend to be regularly formatted - but not always, and it's tough to catch all the edge conditions. Depending on your volume and how close you need to be to perfect, this may or may not be much of an issue.

• Not every bounce message contains the original address that you sent to. It may have been changed en route via a forwarding mechanism, or it may simply be missing. Recognizing who such a bounce is for is tricky.

• Not every bounce is accurate - I've seen "successful delivery" notices that actually indicate failure, for example. Also, a message that bounced today might deliver tomorrow, depending on the cause of failure.

Good luck!

Peace,
-McD