I used the transparent mode to intercept the messages on port 25. If don't use transparent mode won't the messages go straight to my barracuda as I have a static NAT translation directing smpt traffic to it's internal IP bypassing the Astaro alltogether? If I do disable that nat statement will the Asatro just pick up that traffic without some sort of nat statement?

One more thing...I do need to send outbound e-mails, just not from any other domains except for the one I've specificed. So do I still need to add hosts to the allowed hosts field, maybe just my exchange servers?

Sorry for all of the questions.