Work Emails and Expectations of Privacy

Most employers have a policy that emails sent from work computers are considered private, or, more likely subject to monitoring/inspection by the employer.  But, what happens when employees have been using work computers and then the company implements a policy where emails are subject to monitoring?  At least one court has held that the employee should take some affirmative steps to protect those prior emails if he/she later wishes to claim there was an expectation of privacy.  In U.S. v. Hamilton, 701 F.3d 404 (4th Cir. 2012) the Court focused on after the policy’s implementation the employee took not steps to alert his employer; or, archive and delete the emails on his own, even over amicus by the Electronic Privacy Information Center.