Long story short in testing 03 to 10 migration I:
Migrated User1 from E03 to E10.
New local move request.
Couldn't get the E10 working
Removed the move request to move back
Migrated User1 from E10 to E03.
Attempt #2, I cleared all move requests
selected all and did a new local move request from E03 to E10
All mailboxes are good except for user1
User1 is listed as legacy mailbox in E10 and I can't issue a local move request
The 'move request' folder is clear
When I try and login as the user I get this: (via owa)
Your request couldn't be completed because no server with the correct security settings was found to handle the request. If the problem continues, contact your helpdesk.