Introduction

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 could directly connect to the mailbox server role. The CAS role was extended even further in Exchange 2010 and included some new features, including functionality that will change the architecture of every Exchange deployment. At that time, the connections to public folders were still made by MAPI clients to the mailbox server role; connections from these clients to Exchange 2010 mailboxes were handled by the CAS role.

In this latest release, with Exchange 2013, Microsoft has simplified the CAS role. The CAS role is now stateless, which means that it does not save any data. Its job is more or less to help the clients to find a route for connecting to the mailbox or any required service, such as ActiveSync; in short, it is a proxy server. This major architectural...