At the moment, Messenger Plus! (or Windows Live Mail for Windows Live Messenger users) is the only way to get somewhat real-time mail notifications (I say somewhat because they poll for new messages and then notify you rather than stay on a TCP connection where the server could send you mail notifications by the time they’re intercepted, or in terms of POP3/IMAP, actually read the incoming mail and notify in real-time by the time it’s received). But if I’m successful with a solution to get the real account thing a reality, we could get the e-mail notification stuff dealt with server-side. 