Putting a mailbox on litigation hold
When you place a mailbox on litigation hold (sometimes referred to as “legal hold”), Exchange stops removing items when their deleted items retention period expires, and any attempts by the user to delete or change items are retained in the dumpster. Items remain in the dumpster indefinitely until the litigation hold is released and are not subject to any quotas. Because items are retained, they remain available to be indexed and can be retrieved by discovery searches (see the section Discovery searches later in this chapter).
Exchange 2010 RTM only supports placing a mailbox on litigation hold using the Set-Mailbox cmdlet. For example:
Set-Mailbox -Identity 'Ruth, Andy (VP Sales)' -LitigationHoldEnabled $True ...