Exchange migration from 2010 to 2016. I have been testing by moving some mailboxes over to 2016 server and switching incoming to new server but the incoming mail will not deliver to 2010 mailbox. If I have incoming port 25 going to 2010, mail sits in the queue for a bit then gets delivered to 2016. If I set port 25 to 2016 server, it sits in the "smtp relay to mailbox delivery group" queue and never gets delivered to the 2010 mailboxes. Am I missing some kind of connector?