I am in the process of migrating our Exchange Organisation from 2010 SP1 to 2010 SP3 CU9, this has involved building two new 2010 SP3 CU9 servers and a new DAG due to a very unhealthy 2010 SP1 installation. For reference, we have:
EX1 - 2010 SP1 - in DAG with EX2
EX2 - 2010 SP1 - in DAG with EX1
EX3 - 2010 SP3 - in DAG with EX4
EX4 - 2010 SP3 - in DAG with EX3
We have migrated all archive, arbitration and user mailboxes from the old DAG mailbox databases and moved the public folder replicas over to EX3/EX4, which works fine.
As we are coming from 2010 SP1, we must "force" the Outlook clients to update their CAS address by making the old EX1/EX2 servers unavailable, forcing them to auto discover the new CAS array address. This is where the problem lays.
We removed EX1 and EX2 from all Send Connectors, remove their DNS records and shut the servers down so for all intents and purposes, the clients think they are not accessible.
Once the servers were shut down, no email was delivered - not internally or inbound from external. The messages were showing in the Queue Viewer as waiting, and shadow redundancy was showing the messages as queuing to the old, shut down servers (as expected), but the message was not being delivered - even know the destination mailbox was on EX3 or EX4, even mail which was destined for mailboxes on the same mailbox database was not being delivered.
EX3 didn't show any errors, however EX4 showed "Local loop detected", but nothing else of help was listed in the Event Viewer.
Am I missing something, or should this work as I expect it to? Any assistance is greatly appreciated.