Okay, this scenario is based around someone’s exchange mail having gone missing (largely); so their mailbox is still there, but they’ve lost a lot of mail due to faulty archiving.
- Back up current mailbox contents to a PST
- Delete user and mailbox*
- Restore exchange mailbox store from backup (to recovery storage group)
- Dismount "live" store; copy .stm and .edb from recovery group to "live" location
- Enable database over-write
- mount copied store
- create matching AD user without any mail features
- Reconnect user mailbox to new AD user
*This might work just by removing users exchange featurs rather than deleting AD account but untested.
This will be edited, I just had to note down the steps while it was still fresh in my mind.