If you're looking to do your own Hotmail, we've been developing exactly such a system to plug into any domain to offer unlimited webmail accounts. It uses PHP, MySQL and a tiny bit of Perl. Users can sign up, send/receive mail, address books, etc.
The webmaster can control everything, suspend users manually or automatically, send mailshots etc, and lots more. It's secure, fast and easy.
Email me off list if you like, I can show you a demo.
We also have a version that just checks any POP account.
Note, AFAIK, Imp works for IMAP mail not POP mail. It's a bit different to our system, probably more complex than ours, I'd imagine.
paul_AT_genie.ie
