How to migrate Client Access to Exchange 2010

[tweetmeme source=”stalehansen” only_single=false]The Exchange Team has written several blogs about how to transition the Client Access server to Exchange 2010.

The first blog titled Transitioning Client Access to Exchange Server 2010 and can be found here: http://msexchangeteam.com/archive/2009/11/20/453272.aspx

To sum it up you must transition the “Internet Facing AD Site” associated with your external Autodiscover record, then regional Internet facing AD Sites, and then transition your internal Active Directory sites. It is not supported to transition an internal Active Directory site before all your Internet-accessible sites have been transitioned.

The second blog titled Upgrading Outlook Web App to Exchange 2010 and can be found here: http://msexchangeteam.com/archive/2009/12/02/453367.aspx

It discusses how Outlook Web App will function in an Exchange 2003 or 2007 environment that has Exchange 2010 deployed for the end users. Essentially, Exchange 2010 CAS does not support rendering mailbox data from legacy versions of Exchange. Exchange 2010 CAS does one of four scenarios depending on the target mailbox’s version and/or location:

If the Exchange 2007 mailbox is in the same AD Site as CAS2010, CAS2010 will silently redirect the session to the Exchange 2007 CAS.
If the Exchange 2007 mailbox is in another Internet facing AD Site, CAS2010 will manually redirect the user to the Exchange 2007 CAS.
If the Exchange 2007 mailbox is in a non-Internet facing AD site, CAS2010 will proxy the connection to the Exchange 2007 CAS.
If the mailbox is Exchange 2003, CAS2010 will silently redirect the session to a pre-defined URL.

Note: For the purposes of this discussion it is assumed you are utilizing Forms Based Authentication for Outlook Web App authentication.

The third blog titled Upgrading Exchange ActiveSync to Exchange 2010 and can be found here: http://msexchangeteam.com/archive/2009/12/08/453472.aspx

The blog discusses how Exchange ActiveSync will function in an Exchange 2003 or 2007 environment that has Exchange 2010 deployed. Some may have environments that have Internet facing AD sites and non-Internet facing AD sites. As part of our upgrade process, you will be following a model where:

Ensure all legacy Exchange 2003 servers are at latest Service Pack level
Deploy Exchange 2010 CAS, Hub Transport, and Mailbox in the “Internet Facing AD Site”
Have legacy Exchange servers in the “Non-Internet facing AD site” (if they exist)

The simple version is that if configured correctly Exchange 2010 will proxy for the legacy server like this

Exchange CAS2010 will authenticate the user
Determine the mailbox version to be legacy Exchange (2003/2007)
Look up legacy server FQDN on AD
The legacy server will authenticate the user again and will provide the rendered data back to the CAS2010 server
CAS2010 will expose the data to the end user

There is also possible to update the Outlook Mobile version on Windows Mobile 6.1 using Exchange 2010 for users hosted on Exchange 2010. This is done by enabling AllowMobileOTAUpdate on the users Activesync Policies. This is the same version that comes with Windows Mobile 6.5. New features in Outlook Mobile: