Mail over the interwebs

Coldtobi has a list of the free web-accessible email clients. Horde seems like a good choice, in which case, some performance hints might come in handy.

Others to check out: Kerio MailServer.
I haven't yet tired to figure out where that fits into this:
RoundCube = Squirrelmail = Horde != Zimbra = Bongo (old:Hula Project) = OpenExchange = Exchange