I have deployed a new Exchange 2007 server in to an existing Exchange 2003 setup. Everything seems to have installed correctly and the servers see each other as there are 2 administrative groups not visible. The bridgehead connectors were auto-created and I am able to move mailboxes across to the new server. Problem is that when an inbound message comes in to a mailbox that is located on the new server, it gets stuck in the "2003SERVER-2007SERVER (Routing Group Connector)" or "Messages queued for deferred delivery" in the queue. My default SMTP Connector in Exchange 2003 was set to deliver through a smart host but I've tried switching that back to DNS but with no luck. All other messages inbound/outbound work on the 2003 server but can't seem to get anything to route to the 2007 server.
What am I missing to get this to work?