You have an Exchange Server 2010 organization.  Company policy states that a copy of a users mailbox must be kept for one year after the user leaves the company.  All user accounts are in an organizational unit （OU） named OU1.  A compliance administrator plans to export the mailboxes to personal folders.  You need to recommend a solution that allows the compliance administrator to meet the requirements ofthe company policy.  What should you include in the solution？（）