Exchange 2010 includes Personal Archives, a feature designed to help you reduce the risks from PST files and reduce the costs of discovery. Organizations can provision archive mailboxes for their users, allowing them to store older e-mail that's accessed less frequently in the archive. From the user's perspective, archive mailbox behaves like a PST file, minus the file management overhead and risks of a PST file. For more details, see Understanding Personal Archives in Exchange 2010 documentation. Also check out Exchange GM Perry Clarke's Geek Out With Perry series for a chalk talk video on Exchange Archiving.
In the Exchange 2010 RTM timeframe, users could use Outlook 2010 or Outlook Web App (OWA) to access archive mailboxes. This update extends archive support to Outlook 2007.
Read more at source: http://msexchangeteam.com/archive/2010/12/20/457238.aspx
Download it from here: http://support.microsoft.com/kb/2479671