Run the cleanup agent in Exchange System Manager. Expand the Store where the mailbox resides | right-click Mailboxes | click Run cleanup agent.
This marks all orphaned mailboxes with a red cross icon superimposed.
Now you can reconnect the orphaned mailbox to another user account that isn’t (already) mailbox-enabled. Right-click the orphaned mailbox | click Reconnect.
Type in the name of the user you want to reconnect it to, or click Find and look for the user.
Check the bold above and using the same name may well cause issues
#### Answered By John Bostock – Exchange Me! ####