What to do if exchange Server 5.5 in your organization in order to upgrade to Exchange Server 2007?

You cannot upgrade an existing Microsoft Exchange Server version 5.5 organization to Exchange Server 2007. You must first migrate from the Exchange Server 5.5 organization to an Exchange Server 2003 or an Exchange 2000 Server organization. Then you can transition the Exchange 2003 or Exchange 2000 organization to Exchange 2007.