Hey all, just to weigh in here ... I too have tried to turn this on for a cluster of boxes, and I don't see any real performance hit, nor do I actually see anything tagged. On top of that, I have a domain here that we have DKIM records setup for, as well as we sign the outbound messages. With that said, I actually tried sending a message inbound to my account, from and outside SMTP, posing as a user on the domain. Obviously when the mail goes out from this standalone SMTP, and hits the cuda, it doesn't have a DKIM signature on it. I have enabled DKIM inspection on the cuda, and have also said "inspect all mail for DomainKeys Policy" so I would expect the cuda to block this inbound message, but it doesn't.
Can anyone from Barracuda Networks weigh in here?