Able to send, but not receive email

[dtrotter]

This is the third production ISPConfig server i have built, and I am confiused as to why, adter a clean new server build and ISPConfig installation I am able to send from all of my domains (from a client on my machine as well as web based email), but I am never able to receive on any of them. For example, I email myself at gmail, and I receive the email in no time at all, but when I reply I never get it... and it never gets rejected either. Maybe I am overlooking something as it is a little late, but...

Well, thanks in advance.

dtrotter