Exchange Server always lacked in the high availability department. Sure, since Exchange 2000, it had clustering and 3rd party applications extended this option to provide redundancy for mailboxes across multiple sites, but the general feeling I got from using these mechanisms, is that they were less than perfect. Now, with Exchange 2007, Microsoft re-engineered it’s cluster services which now also includes log shipping and DRM (they call it CCR) capabilities.
Watch these features in action with Exchange 2007 Beta 2 here:
http://msexchangeteam.com/archive/2006/08/09/428642.aspx