Need to associate Exchange mailbox from user X to user XY

Situation:

We accidentally deleted a user from AD who has an Exchange mailbox. The mailbox remained intact. We subsequently recreated the user in AD, but we are having issues with some third party software, SIDs etc. We therefore created a new, unique AD account for the same user with a differing alias, User Name etc.

We want to use this new account, and therefore need to associate the Exchange mailbox from the old account, to the new account.

I've seen that you can delete the account from AD (which orphans the mailbox), run the Exchange Cleanup Agent to mark the mailbox as orphaned, go into Disconnected Mailboxes, right click and Connect.

Deleting the original AD account is not an option so this is not possible.

We've updated the User Principal Name in the mailbox and everything in AD and Exchange suggests that when the user logs in under the new account, Outlook should simply open up to her original mailbox.

Any insight is appreciated.

At least in Exchange 2010, you can use the disable-mailbox cmdlet in the exchange shell:

Disable-Mailbox -Identity [email protected]

The mailbox will immediately show up as a disconnected mailbox and can be connected to any account that does not have a mailbox associated with it. The AD account is not affected (other than to have its exchange properties removed, of course).