I have exactly the same problem here with exactly the same symptoms. Mac OS X 10.6.8 with Kerberos, CRAM-MD5, Login and PLAIN methods enabled. We have about a hundred users authenticated all the time and they use PCs Macs, mobiles... with different setups... I spent number of hours trying to get a test message but no success so far. I even tried a completely different Mac server at another company and got the same result. There is no point to show my logs as they are identical to the ones mentioned before and that is how I found this thread. It basically means that SnomOne email facility is unusable on a standard Mac Server. Otherwise it is a great product and a pleasure to work with. I am willing to participate in any tests to get it right.