@Floyd:
you may be oversimplifying... if webmail is pointing UebiMiau (if I recall, this is the default), it reads email through POP3.
A better test for user msites would be to test squirrelmail, which uses IMAP. If that works, then the problem is most likely with Apple Mail.
@msites:
Your posts made no sense attached to a previous thread about another issue. I've made it into a new thread.
If squirrelmail works but Apple Mail doesn't work with IMAP, then you should check your server to make sure that your IMAP daemon is running, and that you haven't blocked it by accident with a firewall setting.
If it's not your server, you need to check with your hosting company.
Jeff