How to add additional servers to Exchange 2010 Routing Group Connector

Issue: You need to add additional Exchange 2010 Servers to the Routing Group Connector used for co-existence with Exchange 2003.

Background: Routing Group Connectors are used to allow mail-flow between Exchange 2003 and Exchange 2010 When you are running a co-existence.

The Routing Group Connector that is created by default during installation of Exchange 2010 will only add one Exchange 2010 server as a bridgehead.  If you have multiple Exchange 2010 servers with the Hub Transport role then you may want to add them to the Routing Group Connector connector for redundancy purposes.

Solution A: If all your Exchange 2010 Servers with the Hub Transport role are in the same Active Directory Site you can simple add them to the existing Routing Group Connector.
1) Open Exchange Management Shell and enter: Get-RoutingGroupConnector

If you just have the default routing group connector created during install you can use the command:
Get-RoutingGroupConnector | Set-RoutingGroupConnector -SourceTransportServers Server1.domain.local, Server2.domain.local

Note: You may need to restart the following services on Exchange 2003 for the changes to take effect: SMTP, Microsoft Exchange Routing Engine service, and the Microsoft Exchange MTA Stacks.  Additionally restarted the Exchange Transport Service on you Exchange 2010 servers.  It may take a few minutes for the new Routing Group Connector to appear in Exchange Management Console.

Solution B:
If you have Exchange 2010 Servers in multiple sites you should create a new Connector.

First you need to Suppress Link State Updates on Exchange 2003 or 2000:

1. Open Registry Editor.
2. Locate HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\RESvc\Parameters.
3. Right-click Parameters and select New | DWORD value. Name the new DWORD value SuppressStateChanges.
4. Double-click SuppressStateChanges.
5. In the Value data field, enter 1.
6. Close Registry Editor and then restart the Simple Mail Transfer Protocol (SMTP) service, the Microsoft Exchange Routing Engine service, and the Microsoft Exchange MTA Stacks services for the change to take effect.

Next create the new connector from Exchange Management Shell:
New-RoutingGroupConnector -Name “Interop RGC MAIN-SITE” -SourceTransportServers exchange2k10A.domain.local, exchange2k10B.domain.local -TargetTransportServers “exchange2k3.domain.local” -Cost 10 -Bidirectional $true -PublicFolderReferralsEnabled $true

Note: You may need to restart the following services on Exchange 2003 for the changes to take effect: SMTP, Microsoft Exchange Routing Engine service, and the Microsoft Exchange MTA Stacks.  Additionally restarted the Exchange Transport Service on you Exchange 2010 servers.  It may take a few minutes for the new Routing Group Connector to appear in Exchange Management Console

In Conclusion, in order to test the new or modified routing group connector you will need to shutdown or disable the initial Exchange 2010 servers that were in the Routing Group Connector to see if the Exchange servers that were added today will route mail to and from Exchange 2003 (use test accounts on 2003 and on 2010 and send mail back and forth).