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 +OK PASS ********** +OK User successfully logged on. LIST +OK 70 8340467 1 30838 2 30838 3 30838 QUIT +OK Microsoft Exchange Server POP3 server signing off.