Having problems accessing some email accounts this morning. The exchange with their tech support ended with this :
Your connectivity is perfect. All I can suggest is using another email client, another PC and if possible disable your firewall if you run one. If you can connect just fine at http://mail.yourdomain.com then the issue must be client related.
That’s the geek way of saying “I’ve run out of ideas, you’re on your own.” One reset of the computer later and all is fine.