I have been experiencing similar problems with my connection working in some locations and not in others. It seems to have something to do with what software is being used at the location to block "inappropriate use". What I'm wondering is whether it's actually a timing issue with the firewall delaying the packets or if it is the actual port being blocked. At other times, the messages have indicated that the connection timed out.
As with some of the other people on this forum, my error message is
The server error encountered was: Mail was unable to connect to server “mail.mac.com” using SSL on port 993. Verify that this server supports SSL and that your account settings are correct.
From these locations, I am able to go to the
http://www.mac.com site. However, sometimes, the messages take a very long time to load or never complete loading. I don't know if this could be a connected problem. The places where I have the most problems with mail via www.mac.com are also the locations where the mail application has problems.