We have added an Exchange 2010 Server to our existing 2003 setup. It is setup as Mailbox, client Access, and Hub Transport. We moved several mailboxes over and for a couple days everything ran OK. Now users with mailboxes on 2010 are not able to send to users on 2003. The error in the queue is:
The 'Remote delivery' queue (MACFEXC\2221) on server MACFEXC is in retry status. Number of message(s) in the queue: 64. Last error information: 451 4.4.0 Primary target IP address responded with: "500 5.3.3 Unrecognized command." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts.
We have deleted the routing connector and recreated, but that hasn't had any effect.