I'm having some problems with message transfer from my Exchange 2003 server (ISA 2004 secureNAT client) to Exchange 5.5 server in branch offices. I'm getting MTABindBack errors to one server, and looking through the ISA logs, it is showing the bindback as "unidentified IP traffic". The intial connection is shown as RPC. I have a second server that I successfully sent mail to this morning (at the same time the first one wasn't working properly) which is now failing with the same problem. I have not changed the ISA configuration today. I swear. The only thing I did today was to restart the MTA services on Exchange to see if that was a problem. the ISA rule I have is to allow Exchange RPC Server, RPC (alll interfaces), RPC Server(allinterfaces) from Internal to Internal. It just looks to me that ISA isn't seeing the bindback as RPC traffic and thus denying it. Do I need to modify this some way? Jeff