The Client Access Server (CAS) role was introduced in Exchange 2007 to provide a dedicated access point to various services such as Outlook Web Access (OWA), ActiveSync, POP3, and IMAP4 to clients. However, all MAPI clients connected directly to the mailbox server role. The CAS role has been extended even further in Exchange 2010 and includes some new features, including functionality that will change the architecture of every Exchange deployment. In this latest release, even though connections to public folders are still made by MAPI clients to the mailbox server role, connections from these clients to Exchange 2010 mailboxes are now handled by the CAS role. This is a major architectural shift, and many of these new features, such as configuring the preferred MAPI endpoint for Outlook clients, can only be managed from the shell.

In addition, with all of the possible ways to connect to Exchange through CAS services such as OWA and ActiveSync, there are a large number of settings...