MSExchangeTeam blogged how to publish Exchange Server 2010 on ISA Server 2006 SP1, it also covers some transition scenarios.
While ISA 2006 SP1 includes a Client Access Web Publishing Wizard for both Exchange 2003 and Exchange 2007, the wizard does not have any knowledge of Exchange 2010. Exchange 2010 includes the following changes with respect to its URLs and virtual directories:
- Exchange 2010 Client Access Servers (CAS) no longer utilize the /exchweb virtual directory.
- Exchange 2010 CAS no longer utilizes the /unifiedmessaging virtual directory.
- Exchange 2010 CAS provides a new solution for managing end user configuration (e.g. Unified Messaging settings), end user self-service (e.g. message tracking), and organization-specific activities (e.g. records discovery), known as the Exchange Control Panel. This service is provided via the /ecp virtual directory and is accessible directly or through Outlook Web Access.
- Exchange 2010 CAS does not render data from legacy mailboxes. Instead, depending on the protocol and/or client, Exchange 2010 CAS will either proxy, redirect, or provide direct access to the appropriate version of Exchange (Exchange 2003 Front-End, Exchange 2007 CAS, or Exchange 2003/2007 Mailbox). Redirected clients access their information via a new namespace, legacy.contoso.com. For more information, please see the post entitled, Transitioning Client Access to Exchange 2010.
Read more at source: http://msexchangeteam.com/archive/2009/12/17/453625.aspx