Outlook Web Access for Exchange 2000

Outlook Web Access (OWA) is a Web-based client that lets users access their Microsoft Exchange mailbox from a Web browser. Although OWA isn't a replacement for the Microsoft Outlook client, it is a feature-rich Web-based substitute for users who are connecting remotely over slower—than—LAN speed connections.

To ensure that your OWA implementation provides trouble-free Web-based connectivity to your Exchange 2000 Server environment, you need to understand OWA's features and limitations and know how to configure the product optimally for your situation. Let's review OWA for Exchange 2000's (OWA 2000's) features and limitations, what's new in this version, and the default configuration. The articles in the Web-exclusive "Related Reading" box provide a deeper look at some OWA features.

Features and Limitations
When Microsoft first released OWA for Exchange, the product was clunky at best and, to most users, downright unusable. However, with each Exchange service pack, OWA became more stable and feature rich. With Exchange 2000, OWA has reached the point at which most users will find it a valid alternative to the Outlook client when they're accessing their mailbox from a low-bandwidth, remote connection. For users who need little more than basic messaging or who move between workstations, OWA might even become the preferred client. OWA's features include an improved UI, a new architecture, direct URL access, better control over access, and the capability of using virtual servers and front-end servers.

User interface. OWA 2000 closely resembles the Outlook client interface, as long as the user is accessing it through the Microsoft Internet Explorer (IE) 5.x browser. Only IE 5.x supports the extensive use of client-side scripting, Dynamic HTML (DHTML), and XML that OWA uses to provide a rich and intuitive user environment. IE 5.x also provides drag-and-drop capability, right-click context menus, tree-based folder display, preview pane display, embedded items (i.e., contacts and messages within the email message), public folder access to Calendar and Contacts subfolders, and Kerberos authentication.

To maintain backward compatibility, OWA works with other browsers (e.g., Netscape, earlier IE versions). However, because these browsers don't fully support technologies such as DHTML and XML, the interface is a lot less rich. IE 5.x helps you minimize user training and complaints because users see a Web-based interface that closely resembles the messaging client they currently use. Figure 1 shows the interface difference between an IE 5.x and a Netscape browser. As you can see, the interface using IE 5.x has a look and feel like the desktop Outlook client, whereas the Netscape interface is so different and feature poor that most users will decline to use it. Some features that the IE 5.x interface has that Netscape lacks are drag-and-drop capability, folder views, and smart windowing for items such as the address book.

New architecture. Beyond the user experience, OWA 2000 is dramatically different from its Exchange 5.x predecessors. With Exchange 5.x, OWA uses Active Server Pages (ASP) scripts to communicate directly with the Exchange server, which runs Collaboration Data Objects (CDO) and Messaging API (MAPI). Versions earlier than OWA 2000 use the IIS server for most of the script and MAPI processing, which limits the number of users that can be serviced at one time because of the processor resources that the server needs. Larger organizations must load-balance several OWA servers to provide their users with reliable and timely access.

OWA 2000's new architecture is more streamlined and can host many more simultaneous user connections. OWA 2000 is no longer part of IIS; it now resides in the Microsoft Web Storage System (WSS) and uses IIS only to receive and forward user requests. Although IIS still uses HTTP, the elimination of ASP scripts and MAPI management greatly reduces server processing so that one server can handle many more client sessions.

Direct URL access. OWA 2000 now provides direct-named URL support for folders and resources within the Exchange Information Store (IS). OWA 5.x uses a long, complex globally unique identifier (GUID) embedded within the URL for direct folder support. This scheme in older OWA versions makes direct-resource connection difficult for most users and Web administrators. OWA 2000 has simplified this resource request by using an intuitive plain-text URL. For example, when test user Abraham Lincoln wants to connect directly to his calendar rather than go through the default main page, he now can type

http://exchange/alincoln/calendar

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