Applies to: Exchange Server 2007 SP3, Exchange Server 2007 SP2, Exchange Server 2007 SP1, Exchange Server 2007
Topic Last Modified: 2008-04-17

In Microsoft Exchange Server 2007, the sizing of Client Access servers is performed differently from the sizing of front-end servers in previous versions of Exchange. The architecture changes in Exchange 2007 have moved most of the client-specific functions from the Mailbox server to the Client Access server. For more information about the functions and features provided by the Client Access server, see Client Access.

In Exchange 2007, messages are converted on the Client Access server when they are accessed by a non-MAPI client (for example, Internet Message Access Protocol 4 (IMAP4) or Post Office Protocol 3 (POP3) clients). In addition, rendering for Microsoft Outlook Web Access is performed on the Client Access server, as opposed to the Microsoft Exchange Information Store service, which rendered Outlook Web Access in previous versions of Exchange.

The Client Access server also offloads many stateless tasks from the Mailbox server (assuming the roles are installed on different physical servers), and provides a unified namespace so that users need only point to a single name regardless of which Mailbox server hosts their mailboxes. In addition to the Internet protocols, such as IMAP4, POP3, and HTTP, the Client Access server also provides Outlook Anywhere (formerly known as RPC over HTTP), ActiveSync, Autodiscover, Availability service (which includes all free/busy information in topologies that do not use public folders), and Web services. These architectural changes allow the Client Access server to offload significant processing from the Mailbox server.

General Sizing Recommendations

To ensure that you are reading the most up-to-date information and to find additional Exchange Server 2007 documentation, visit the Exchange Server TechCenter.

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