processing email

I want to write an application that's almost like a webmail, but not quite. It must receive emails from several mailing lists, store them in a database, allow making annotations, provide some kind of accounts with passwords, etc. It's quite specialized, it cannot be used as a webmail proper, nor a webmail can be used instead (and that's why i'm writing it). But i do not want to reinvent the wheel. Are there any PHP libraries or something to process email? E.g., for things like "here's the message, separate the headers from the body and do something different with each other item" or "find a discussion thread in these emails if i give you the headers of each message". Things like that. BTW, i will use PHP-4.3 -- Florin Andrei http://florin.myip.org/