Although many of the new features in Exchange 2010 are redundant by design and have been designed in that manner, this does not negate the requirement for a reliable disaster recovery plan.
The inherent features of Exchange 2010 will contribute toward maintaining high availability and in doing so provide the first option of recovery during a disaster.
What you may have to recover from:
Many types of failures and disasters may require that the Exchange administrator repair or restore complete Exchange 2010 messaging system. It is important that you have a strategy in place to recover from this kind of situation where you lose the complete infrastructure and sites (including all Exchange servers and all servers that provide external services).
The root causes for these situations could be:
When the disaster recovery solution is configured, you will have Exchange 2010 service availability in DR site, however to make it operational you need to have the below infrastructure in place before activating the Exchange 2010 in DR site
“Dial Tone” Recovery:
The Microsoft Exchange Server 2010 dial tone recovery feature offers the following:
Exchange 2010 “dial tone” portability further enhances the “dial tone” recovery scenario, by allowing a “dial tone” recovery to take place on any Exchange 2010 mailbox server in the Exchange organization. This allows an alternative server to host the mailboxes of users who were previously on a server that is no longer available. However, the dial tone recovery should only be needed when the complete messaging infrastructure is down. Clients that support Autodiscover, such as Microsoft Office Outlook 2007 or Microsoft Office Outlook 2010, will automatically be redirected to the new server without having to manually update the user's profile.
How “Dial Tone” works with database portability:
The Exchange “dial tone” portability feature provides recovery from site-level disasters by:
“Dial tone” portability allows a user's mailbox to be moved without having access to any of the mailbox content. This allows an alternative server to house the mailboxes of users who were previously on a server that is no longer available. With the Outlook and Exchange Autodiscover service, clients are redirected to the new server when they try to connect. Users are then moved to this new server and quickly regain the ability to send and receive e-mail messages.
The detailed step by step guide on how to perform dial tone recovery is outlined at: