I'm currently transitioning from Exchange 2003 to Exchange 2010 but my split domain/namespace has stopped working - although it took a week to stop!
We have a namespace which was split between two Exchange 2003 servers in separate Admin groups - one in UK, one in Australia. We then had a connector routing this specific domain between these two servers. All was working OK.
We have now installed an Exchange 2010 server into the UK Admin group and initially all was OK. However, the split domain changed itself (at least I'm not aware of a manual change) from Authoritative to Internal Relay domain. This resulted in NDRs being generated when sending into this domain from external sources (UK only - Aus was still receiving OK).
We changed this back to Authoritative and external mail now being received. But when I send an e-mail to this domain for an Australian recipient from a mailbox on my Exchange 2003 server I get "A configuration error in the e-mail system caused the message to bounce between two servers or to be forwarded between two recipients. Contact your administrator." error message.
If I send it from a mailbox on my Exchange 2010 server then it's delivered OK.
I've tried removing my UK Exchange 2003 connector.
I've tried pointing the Smart Host for this connector to my Exchange 2010 server
I've tried setting up a separate SMTP Virtual Server on my UK Exchange 2003 server
All of which result in the same error message.
Message tracking indicates that it's not leaving my UK Exch2003 server and generating the NDR from there.
I can't really find any config guides about split domain involving 3 servers or from transitioning a split domain from 2003 to 2010.
All e-mails from Aus to UK (Exch2003 & 2010) are received OK.