Can someone confirm my understanding on this, below is what i believe to be correct RPC Client Access Service The change in Exchange 2010 to move all processing to the Client Access server was implemented to provide all data access through a single, common path of the Client Access server. This change improves consistency for applying business logic to clients, and provides a better client experience when failover occurs. This change also allows a higher number of concurrent connections per server and a higher number of mailboxes per server because the number of RPC Client connections in exchange 2007 is limited to 60000, server 2008 changed this value by instead of a connection being source port and ip, it allowed source ip and up to 60000 ports. The Exchange store process is limited to 65565 contact handles, when you have 4 connections per client it takes the number down to 15000 connections, then consider mailbox sizes etc and that number reduces the number of mailbox connections even more. In Exchange 2007 the mailbox server would have all the mapi clients connections, instead the mapi connections are with the CAS array, the CAS server has 100 rpc sessions available for mailbox data connections, as these are sessions they can be connected and disconnected as and when require reducing IO impact on the Exchange mailbox server. ABS replaces DSproxy interface that resided in system attendant on mailbox server. In versions of Microsoft Exchange earlier than Exchange Server 2010, Exchange provided a referral service that told clients such as Outlook where they could find a server running the NSPI service. This referral usually pointed Outlook to a global catalog server. But some Outlook Anywhere connections would point Outlook back to the local server, and the NSPI calls would be proxied to a global catalog server. Outlook expects to find this referral service on the same server that's used for mailbox access. In Exchange 2010, both mailbox access and directory access are handled by the Client Access server. So in addition to moving processing of incoming Outlook connections to the Client Access server, in Exchange 2010, directory access is also handled by the Client Access server reducing IO impact on the mailbox server. In Exchange 2010, Exchange 2010 mailbox outlook clients use the CAS array/Server for ldap lookups, Benefits of RPC Client Access Service - reduces IO footprint on the mailbox server role, allows for DAGs as AD maps mailbox to database not server?Thanks for any reply

Hi,Yes, your understanding is basic correctly. In Exchange 2007, Outlook clients 2000 and later version use the referral service to connect directly to the GC. However, the Referral Service will refer clients back to DSProxy (NSPI proxy) to establish the directory connections. The Referral service will not be used to provide the GC to the client. It still relies on the DSproxy (NSPI proxy).How does Outlook Anywhere workhttp://msexchangeteam.com/archive/2008/06/20/449053.aspxThanksAllen