Route emails internally and to external smart host

I am migrating users from Exchange 2003 to Exchange 2010, cross forest.

I have moved mailboxes and can access them on the 2010 side, I can also send and receive email externally.

I have set up the accepted domain as an internal relay and added a send connector pointing to the Exchange 2003 server.  If I then email to someone on the same domain, within the Exchange 2003, 2010 forwards it to the Exchange 2003 server.  This is perfect.

However, how do I get it to work the other way.

I've tried to create a new smtp connector for the domain, giving it a new smart host and picking that it is to relay to this Exchange.  However, in the queue it simply says submitted to advanced queuing.

How do I get the Exchange 2003 server to do what I have managed to get the Exchange 2010 server to do.

Thanks in advance