It may be as simple as recording the voice name for each mailbox and checking to see if the number of digits on the extensions are both the same on the Telephone system and the TVS50. Make sure your ports are the prescribed ones on the telephone system and the type of integration is correct. I haven't done one of these in a year but actually the quick setup in the TVS50 takes care of the mail boxes pretty well. I'll see if I can dig up a manual for specifics.