Hi I have a Front-end server and BAck-end server running Exchange 2003 in coexistence with 1 CAS/HT server and 1 MB/HT server running Exchange 2010. I have created the Interop RGC connector as follows: New-RoutingGroupConnector -Name "Interop RGC" -SourceTransportServers "EXchangeMBX2010" -TargetTransportServers "ExchangeFE2003" -Cost 1 -Bidirectional $true -PublicFolderReferralsEnabled $true Since then i can send emails from 2003 users to 2010 users correctly but the other way around doesnt work (2010 users to 2003 users). All i receive is a delivery delayed notification: Delivery is delayed to these recipients or groups: Subject: Test This message hasn't been delivered yet. Delivery will continue to be attempted. The server will keep trying to deliver this message for the next 1 days, 19 hours and 51 minutes. You'll be notified if the message can't be delivered by that time.

Have you tried the Email Flow Troubleshooter located in the EMC -> Toolbox node? Run that and post the results.Tim Harrington - Catapult Systems - http://HowDoUC.blogspot.com

The tool is asking for a NDR code which i cant find in the NDR.

Try removing the routing group connector, then creating it fresh, but one way at a time, so you end up with two. Also ensure that the servers can telnet to each other on port 25. You have enabled/checked the relevant permissions on the connectors? Simon.Simon Butler, Exchange MVP. http://blog.sembee.co.uk , http://exbpa.com/