I've just installed Exchange 2010 SP1 on a new server, in a domain that already has an Exchange 2003 Server. I followed the steps in Technet on how to accomplish this, and seemingly all went well. These are the only two exchange servers in the domain.
I moved one test user/mailbox from 2003 to 2010. Everything I've tested works, except if I email the test user from an account associated with the exchange 2003 server. Then the email ends up being queued in the "messages with an unreachable destination" queue
I've enabled diagnostic logging for MSExchangeTransport on the 2003 server and got the following error
MSExchangeTransport / Connection Manager / EventID 4006
Message delivery to the host '192.168.0.2' failed while delivering to the remote domain '_4886135a22abb944886470d7c12473c7_D' for the following reason: The remote SMTP service rejected AUTH negotiation.
Where 192.168.0.2 is the IP of the 2010 Exchange Server
I'm relying on the "routing group connector" created during the install for the communication from 2003 to 2010.
I understand what this error is, but in the context of the "routing group connector" I've no idea how to proceed to resolve what it really means and fix it.
Any and all advice appreciated.