In an attempt to evaluate Exchange 2007, I installed theeval in a small domain that mirrored our production environment, that is a mailbox server and a front end server. Exchange 2007 installation and configuration was easy enough and everything looked like it was working until I tried sending message between servers. Ex2k3 clients were able to receive messages from 2k7 clients, but 2k7 clients aren't receiving messages from 2k3 clients. Does anyone know why this is? Thanks.

Is the E2K7 servers in the same organization as the E2K3 server? Do the E2K3 clients get an NDR message?

Yes to both. It is the same organization and a NDR is received.

I tried using this script to resolve the issue and while it now allows messages to go from 2k3 to 2k7, it no longer allows them to go from 2k7 to 2k3.New-RoutingGroupConnector -Name "Interop RGC" -SourceTransportServers "Ex2007Hub1.contoso.com" -TargetTransportServers "Ex2003BH1.contoso.com" -Cost 100 -Bidirectional $trueAny ideas?