Domino app servers and pop3 servers not communicating

I have a domino 8 server and a pop3 server not communicating. can anyone give insight as to what other trouble shooting techniques would contribute to a remedy to this problem and what can be done? This first thing that comes to mind is DNS and configuration but those both have been checked.

Subject: HI…

Can you be a little more specific? Do you mean that they are not replicating? You cannot trace them?

Did you create connection documents?

If they are created, check the optional network address.