I was able to connect to both your POP and mail server via telnet without any problems.
You may wish to try this yourself, using either of these tutorials:
Also we have been seeing increasing instances of Firewall problems when accessing email, problems that just seem to crop up on a local machine or network, so checking your firewall, if one is involved would be a good idea.
That particular error is connected with many, many email issues both in sending and receiving.
Hope this may help,