@ABCFED, thanks for the detail. That situation certainly isn't "proper" as Exchange expects to be able to perform Exchange Auth between the servers and the fact that you had to enable anonymous tells me something was breaking down there which we could probably diagnose with SMTP logging. Did anyone do something like untick IPv6 from the NIC on either server? The reason I pushed for details (I hope you don't mind) is many times when the 'bug' flag is raised by customers we tend to find it is a misconfiguration in the OS or Exchange. In no way am I saying we don't bugs (hell, this thread is proof enough), but something as core to the product as mail flow between versions is something the whole world would be blowing up about if it didn't work out of the box. :) -b