We use GFI Mail Essentials. According to it mail for the previous 10 hours was coming in to the server but was not showing up in users mailboxes. GFI kind of threw their hands up and pointed the finger at Microsoft. I finally had to break down and restore the OS from backup. Not the data partition (which holds Exchange). It fixed the problem and mail started being put in mailboxes again. Would anyone have any idea where these 10 hours worth of emails went if they actually did come in to the server but were not put in users mailboxes?