If you get an error message when trying to connect to the VPOP3 SMTP/POP3/IMAP4/etc service which says

VPOP3 xxxx Server Access not allowed - See your administrator (where xxxx is replaced with the specific service name, and there may be protocol specific error codes before the message)

This means that there was a problem during VPOP3's startup - usually this is due to a licencing problem.

If you log in as the VPOP3 administrator, then VPOP3 should tell you after login what the problem is, and tell you how to resolve it. Usually it simply involves entering the VPOP3 licence details.