For reasons I won't go into here. I had to restore a person's account who left the company over a year ago, two months ago, that account was finally deleted. Whatever....
Active Directory Recycle Bin in Windows 2012 AWESOME!
As expected it restored the person's email account, great! Next went to restore the person's email which was archived off to a PST. Shouldn't be a problem.
Except it was a problem! I couldn't import the PST, in fact I could not use OWA or Outlook to get into this person's email account. Also errors showed up in Exchange Admin Center. After much digging around we deleted the person's account in Exchange, recreated it, then things started working. Turns out that the default AD retention is 90 days, however in Exchange it was only 30 days. Since the deletion happened roughly 60 days ago, Exchange got confused.