Sorry, wrote my post about Mail after a long ahrd day! I amusing Mail with system 10.4, POP account with messages left on server. Messages can be sent (so log in must be recognised), and Activity Window shows that Mail is connecting to the server, authenticating user and checking for new mail. it fails to recognise mail on the server however. If I go to my other computer, it does recognise and download messages on the server.
As the account details in Preferences are idential, I thought it must have been a problem with my settings in System Preferences, but as far as I can tell those settings are also the same (account details, passwords, settings, etc.). It's got me beat! Bud