With IMAP an email client program can not only retrieve email but can also manipulate message stored on the server, without having to actually retrieve the messages. So messages can be deleted, have their status changed, etc. Nothing new about that. But don’t deploy IMAP if you have lousy connectivity between your IMAP clients (e.g. Thunderbird) and your servers. We are experiencing great difficulties with our users in the far East with regards to accessing the mail stores on the European servers. So bad in fact, that I’m considering degrading them to POP3. I’m currently investigating the situation and trying to find a decent solution which will increase user- acceptance on the one hand, and lower the bandwidth requirements on the other. Oh, and all that of course, without spending a penny cent.