Posting this in case it helps anyone
So I have been trying to move a mailbox from ServerA to ServerB using ExMerge for a few days now and kept getting permission denied no matter how I set the permissions.
Colleague noticed the users were disabled, I knew this but didn't think it would make a difference but it turns out I was able to move non-disabled users mailboxes, so checked online (nothing found on Spiceworks) and it turns out ExMerge will not extract disabled users mailboxes!
I had to re-enable the users and wait a couple of hours and presto I moved the mailboxes to ServerB.
Windows 2000 Server with Exchange 2000, yes I know..... :(
(note before posting - I cannot see the option to say I don't require an answer) - Edit - Marked as discussion