Stuffing the headers (or the entire message) into the database should be reasonably straightforward. I use mailagent to filter incoming mail. That would probably be overkill to parse incoming mail and stuff it in a database, though. Something like MailTools might come in handy.

That said the major issue is creating the appropriate categorization when the emails get inserted so that you can query the database easily afterwards. I think you'll find that to be the tricky part, because categorizing on the fly based on some values in the Subject, From, Cc fields, or in the body of the message will become slower and slower as the database grows.

It's an interesting project, though :-)

Michael