Try Zimbra as a storage engine

The kinds of things you want to do with email once it is in a database... already sounds like what I've been doing with Zimbra for over 4 years now. It has a very extensive search capability and the ability to store searches. To me having a ton of email is no good at all if you can't find what you are looking for.

Zimbra is certainly more than a way to import some email from a source and then search it... it is a complete mail solution with shared documents, calenders, and even IM... but you can do what you want with it... or at least I'd be surprised after looking at if if you thought the search was missing something.