Company XYZ has two locations.
Each location has two servers, one Exchange 2003 and one Exchange 2007. All incoming mail from the internet goes to Server C.
The location on the left is the main office, the location on the right is the branch office.
The default installation of the first exchange server happened to be Server D. This created a connector between the two version.
Unfortunately, Incoming mail from the Interent can be assigned to Server A or Server C, as the location on the Left is where the Incoming connection exists.
The problem exists when mail is sent from Internet to mailboxes that exist on Server A. The mail unnecessarily travels across the WAN link to the branch office, then back to the Main office after going thru the Exchange connector.
This problem is resolved by using the following powershell command to build a connector between Server A and Server C
New-RoutingGroupConnector -Name "Interop RGC" -SourceTransportServers "Ex2007Hub1.contoso.com" -TargetTransportServers "Ex2003BH1.contoso.com" -Cost 100 -Bidirectional $true -PublicFolderReferralsEnabled $true
It’s explained in technet here: How to Create Routing Group Connectors from Exchange 2007 to Exchange Server 2003
Because there is a possibility of looping, you need to Suppress Link State Updates on all Exchange 2003 servers. Instead of traversing the registry, I decided to make a reg file. Just copy and paste the following text to a file called SupressLinkState.reg
Windows Registry Editor Version 5.00
Then double click it, and say yes to this:
Exchange 2007 can’t send mail directly to a 2003 server unless there is a connector between them. The Blue arrows represent connectors, the Black arrows represent built in mail flow based on lookup of mailbox location.
And you can’t modify any of the properties once you do get into it.
Get-RoutingGroupConnector and Get-RoutingGroupConnector | fl for a full listing.