Currently doing an Exchange Project upgrading an environment from 2003 to 2010 and ran into a little problem that was unexpected and have not seen before on past migrations. My engineer figured the issue out and now mail is properly flowing between the internet and the two exchange servers. Apparently, when someone updates the default SMTP virtual server on exchange 2003 and inserts a smarthost on the connector it will break all routing group connectors on 2007 & 2010 exchange servers. Even if you delete the RGC and recreate them on exchange 2010, messages will still fail. This is because the smarthost field is filled in on to the virtual SMTP server. To correct the issue, remove the smarthost entry on the virtual SMTP server, delete the RCG using the exchange management shell (command below), recreate the routing groups (command below), and wait 5 minutes. Everything should be corrected. Now to fix the smarthost error, delete the SMTP connector on exchange 2003, recreate a new routing group connector for SMTP specifying the smarthost under the outgoing settings. Exchange routes correctly.. Good news!
To remove a RCG:
Remove-routinggroupconnector (hit enter to get a prompt of the name of the RCG)
To add a RCG (make sure its bidirectional there are two one for each server so e2k3srvr-e2k10srvr and e2k10srvr-e2k3srvr in this case)
New-RoutingGroupConnector -Name “2003-2010” -SourceTransportServers “e2k3srvr.”clientserver”.net” -Tar
getTransportServers “e2k10srvr.”clientserver”.net” -Cost 1 -Bidirectional $false -PublicFolderReferralsEnabled $true
New-RoutingGroupConnector -Name “2010-2003” -SourceTransportServers “e2k10srvr.”clientserver”.net” -Tar
getTransportServers “.”clientserver”.net” -Cost 1 -Bidirectional $false -PublicFolderReferralsEnabled $true
Last note, DO NOT ever edit anything in ESM on 2003 for the 2010 server, it may take the change but it will not actually process or turn active. At this point the MA exchange 2010 server is ready to be released to production.