Or even better, are there any technical reasons why we couldn't just use email as an IM protocol? I'm thinking an extra header flag to denote that a message is

Or even better, are there any technical reasons why we couldn't just use email as an IM protocol? I'm thinking an extra header flag to denote that a message is an IM would be all thats needed to keep IMs out of your inbox (and then your mail app can separate IMs from emails). Or is IMAP not fast/powerful enough to handle this kind of messaging?