Over the weekend I completed for the most part a migration from single Exchange 2003 to a single Exchange 2010. All mailboxes have been moved and public folders replicated. Email is flowing to and from our domain and OWA is working. The problem I seem to be getting is if I disable the SMTP protocol on the exchange 2003 server than I start getting messages backing up in the queue on the Exchange 2010 server. The messages are related to public folders it appears as normal smtp traffic still flows just fine.
The error is: 451 4.4.0 primary target IP address responded with "4188.8.131.52 unable to connect."attempted failover to alternate host, but that did not succeed.Either there are no alternate hosts, or delivery failed to all alternate hosts.
The From address is showing as my 2010 Public folder database, Message Source is Local, Subject is Folder Content.
I have not yet moved the Public Folder replica as I want to make sure all works before moving. If I re-enable the SMTP protocol on 2003 than messages clear queue. If I look at the recipient Info of one of the messages it is showing as my