Departed employee returned - need access to old email

Situation is I have an employee who departed the company for about two years.  When that that employee left his mailbox was deleted although his AD account was just disabled (we have a policy of never deleted accounts - we just disable so that the same account name can never be used again)

This employee returned to the company and the account was re-enabled and a new mailbox created. 

The employee can now only search for mail in Emailxtender since date of return.  Admins can search for the old email but we would like to give employee access to search this old email too.

Anyone know how to reestablish these permissions?

Thanks!