This is our setup:
3 multi role Exchange 2010 servers (mailbox, hub, and transport) in DAC mode
2 on the primary site and 1 on DR site
All three are a member of a single DAG with database activation Disabled on the exchange server on the DR site
We backup the two primary Exchange servers using Veeam and on that site and we are trying to restore a EDB to one of these servers after removing it from that server. So for a test we created a new Mailbox Store DB called DR_test. We added a mailbox to this and sent it some mail. Next we dismounted it and renamed the .edb file. We then tried to restore the EDB file from the Veeam backup and then remount the store. This is where we get an error (possibly because Exchange see's it as an older file than the one we renamed).
Can get the exact error if needed.
We are also trying a different DR scenario where we are bringing up the 2 primary server vms on to a test network (along with required infrastucture: dns,ad etc) but this is also failing (I think due to the clustering).