Exchange 2007 Roles

A company with a large central headquarters and a smaller branch office will likely configure its Exchange 2007 servers in specialized roles. The headquarters site (shown in top box) has enough users and Exchange traffic to justify having one or more servers dedicated to each role, while the remote office (shown in bottom box) is small enough that a single Exchange server is adequate to handle all roles (except for the edge transport role, which cannot be combined with other roles).

In each site, Outlook 2003 and Outlook 2007 users either use Microsoft’s remote procedure call (RPC)-based Messaging API (MAPI) protocol to connect to their mailbox server or they might connect to a client access server using MAPI RPC-over-HTTP. This latter option allows Outlook users to connect from outside the firewall without the need for a VPN connection. The client access server hosts the Outlook Web Access (OWA) application, which provides an e-mail client to browser users. End users who use a POP3 or IMAP4 client (such as Outlook Express), or an Exchange Server ActiveSync—compatible mobile device (such as a Windows Mobile phone), also connect to a client access server. For all of these clients to access Exchange from the Internet, the firewalls must be configured to forward inbound HTTP, MAPI RPC-over-HTTP, POP3, and IMAP4 requests to client access servers in the sites hosting the users’ mailbox servers (paths not shown in the diagram). Each site’s client access servers use MAPI to access the mailbox servers in the site.