After a migration from Exchange Server 2010 to Exchange server 2013, I turned off the Exchange 2010 Server to ensure mail flow continued before decommissioning it. Users are now getting a ‘Delayed Message’ bounce back when sending email. All mail is stuck in the queue of the Exchange 2013.
When I turned the Exchange 2010 back on again, mail flow was restored and the queue emptied. In testing, when I stopped the service “Microsoft Exchange RPC Client Access”, on the Exchange 2010, the mail was again delayed and stuck in the queue on the Exchange 2013. I restarted that service and everything went back to normal again.
Is there a setting that I can’t see that I should have migrated? Thanks