I often get to configure POP3 on mail environments. The easiest way to test if it works is to use telnet (using built-in or Putty).

First, connect to port 110:

telnet POPserver.domain.com 110

Then run the following to authenticate, list mails and quit. Just change whatever you need in red, domain is not always needed if you have one domain.

+OK The Microsoft Exchange POP3 service is ready.
USER DOMAIN\username
PASS **********
+OK User successfully logged on.
+OK 70 8340467
1 30838
2 30838
3 30838
+OK Microsoft Exchange Server POP3 server signing off.

More info.