A. Exchange 2007 removes Exchange 2003’s database-mounting restrictions.
Exchange 2003 restricts the mounting of an Exchange mailbox database on another server unless you set the restore function to the server-recovery storage group, or unless you restore to a server with the same name and mount the database on another server in the same administrative group. Even considering these limitations, mounting a database in Exchange 2003 is still complicated.
With Exchange 2007, you can mount any Exchange 2007 server on any other Exchange 2007 server within the same Exchange organization. This functionality permits fast end-to-end recovery times and avoids the restore-operation manual steps that often introduced problems.
Once you mount the Exchange 2007 database on another server, you need to update Active Directory (AD) with the change. You need to only update those objects affected by the mailbox move. You don't need to move mailbox data because you already moved the entire database. To update AD with the new server, use the Move-mailbox command with the configurationonly flag, as in the following example:
get-mailbox –database Microsoft Office Outlook 2007 clients will automatically discover the new Exchange server, as will Outlook Web Access (OWA) clients, because they access Outlook through the Client Access server role. You’ll need to manually update pre-Outlook-2007 clients with the new Exchange server that hosts the mailbox. There are a few limitations in Exchange 2007. Database portability relates only to mailbox databases—public-folder databases don't have the same level of portability. You also can't take a database from an Exchange 2007 server and mount it on an older platform. The following table shows your options. 
