This post talks about how you can transition your existing Exchange environment to Exchange Server 2010 from a client access perspective. For most of you, this’ll also mean coexisting with legacy Exchange and Exchange 2010 for a period of time. This post’ll hopefully answer these questions by breaking down your transition into two scenarios: • Transitioning an Exchange 2003 environment to Exchange 2010 • Transitioning an Exchange 2007 (that may or may not contain Exchange 2003 mailbox servers) environment to Exchange 2010. The underlying goal here’s to move your primary namespace, mail.contoso.com and autodiscover.contoso.com, over to Exchange 2010 and introduce a new namespace for legacy access, legacy.contoso.com and associate it with your legacy Exchange client access infrastructure. Users’ll continue to use mail.contoso.com as their access point into the organization for messaging services.
Full Article: Exchange blog