I have Exchange 2007 Sp3. I upgraded to Exchange 2013 with co existence. I have added 2 MBX servers in DAG and 2 CAS servers in clusters. There is ironmail appliance. Now, I am testing the mail flow internally from 2013 to 2007 MBX its fine. But from 2007 to 2013 mail stops in queue. Please help. I think its connectors but I am unable to resolve it. In queue viewer I can see messages.