We still have an old Exchange Server 5.5 running on NT4. It has now been targeted by a number of spammers for transmission of their spam. I am NOT an expert on this, but my understanding is that when someone attempts to send an email to a non-existent address on the server (firstname.lastname@example.org) ES 5.5 will not deliver it, of course, but will allow the server to send it onward to any other recipients that are not in one of our domains. As a result, I think, there are now huge numbers of spam messages being forwarded from our server. We have now been black-listed by Comcast, for example. Since we host mail for about 25 domains, with many of the users off-site, does anyone know of a way to stop this from happening? I set up a new user for the notifications for the admin and now am receiving hundreds of notices of failed inbound emails. I gave up on trying to enter domains in the routing tab of the IMC, as there are just too many and they constantly change. (yes, I know we need to move off of this beast, but that is still a few months away.) Any help is sincerely appreciated.