If you are attempting to diagnose mail on your server or VPS, you can quickly test POP3 without setting up an account in a mail program using telnet :
telnet server-name.com 110 USER firstname.lastname@example.org PASS unencrypted-password here LIST
where email@example.com is the pop3 login your are testing. Usually this is the same as the email address.
List should return the messages number or a single period if no messages are available
Note that in this test the password is unencrypted. You should set a temporary test password during the test.