(BASIC) Architecture Changes:
With Exchange Server 2010 all protocols should go through the Client Access Server and cannot connect to Mailbox servers to MAPI clients directly. This is done by using new Client Access Server(CAS) Windows Server service known as the RPC Client Access service.
How do you deal with a two (2) AD site scenario (i.e cross data center) and you have to redirect Outlook Web App clients between these sites transparently. -> Exchange 2010 SP1 Proxyng
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GAL Segmentation, Exchange 2010 Address policies
The Exchange Customer Experience Team has heard the feedback our customers have provided to us and are now working to incorporate a set of features that will provide a Global Address Segmentation capability directly into Service Pack 2, which will be available to customers in the second half of 2011. We plan on posting more about Service Pack 2 in the next couple of weeks.
This decision was taken in order to simplify the deployment and configuration of the feature for all customers by providing a consistent and controlled experience through the standard Exchange management interface.
As a result of the decision to build the functionality into the product, we have also decided that we will not release an updated version of the Configuring Virtual Organizations and Address List Segregation Whitepaper that was published for Exchange Server 2007
LYNC REACH CLIENT - http://blogs.technet.com/b/toml/archive/2011/02/04/how-to-force-the-use-of-the-lync-reach-client-just-append-this-to-the-url-sl-1.aspx