Suppose one worker sends an ill-considered e-mail message to a coworker at 4:00 pm.  The recipient receives the e-mail the next morning, immediately deletes it, and then phones the sender to make sure the original is deleted as well.  But both people have forgotten about their diligent systems administrator who has the server set to make nightly backups of everything on the system, and then stores those tapes.  Currently, the OS saves backup tapes indefinitely, due to on-going litigation.