How to increase Outlook Web Access performance

This article discusses the various methods that you can use to increase the performance and response of Microsoft Outlook Web Access (OWA) when you use OWA with Exchange 2000.

Use the Reach Version of OWA

There are two versions of OWA, the rich version and the reach version. The version that you use depends on the Web browser that you use to access OWA. If you use Microsoft Internet Explorer 5.0 or later, you receive the rich version. If you use Internet Explorer 4.02 or earlier, you receive the reach version.

The rich version supports rich features, such as dynamic HTML (DHTML), the Web Distributed Authoring and Versioning (WebDAV) protocol, XML, and Extensible Stylesheet Language (XSL). Internet Explorer 5.0 and later are rich browsers, which are sometimes called uplevel browsers.

The reach version does not support these extended feature sets, but does support basic capabilities, such as HTML 3.2 and European Computer Manufacturers Association (ECMA) script standards. Internet Explorer 4.02 and earlier versions of Internet Explorer are reach browsers, which are sometimes called downlevel browsers.

The reach version uses a simpler user interface than the rich version. Because the reach version is designed for browsers that do not have DHTML and XML support, it does not include some of the features that are available in the rich version, including the following versions:

• Advanced view options, such as the preview pane and sorting
• New mail notification
• Search
• Calendar reminders
• Advanced calendar controls and printing
• Public folders
• Drag-and-drop editing
• Tree control

If you use the rich version of OWA, you can take advantage of the client-side Microsoft XML control and make custom HTTP-DAV requests to the server by using verbs such as SEARCH and PROPFIND.

NOTE: Some older proxy servers do not support HTTP-DAV requests and block these requests, which prevents the Web browser from accessing OWA. The reach client is not affected because it only uses standard HTTP verbs, such as GET and POST.

The server determines the version of the client browser by using the User-Agent HTTP header that is sent with every browser request. Based on the information in the User-Agent HTTP header, the server returns the appropriate OWA version for the client browser.

Because of the simpler user interface and limited feature set, the reach version of OWA requires less bandwidth. If you use the rich browser and you experience OWA performance that is not acceptable, you might experience better performance if you use a reach browser of OWA.

Segment Your OWA Installation

You can use OWA segmentation, which is available in Exchange 2000 Service Pack 2 (SP2), to selectively turn on the rich client features of OWA, such as calendaring, contacts, public folders, calendar reminders, and new mail notification. OWA segmentation can also provide server-side control of the rich version of OWA by forcing the use of the reach version, even if the client uses a rich browser.

You can also configure OWA segmentation individual servers and individual users. Settings for individual users override the settings that are configured for individual servers.

For more information about how to write an add-in to segment OWA on an HTTP virtual server, click the following article number to view the article in the Microsoft Knowledge Base: For more information about how to segment OWA on a server or for an individual user, click the following article number to view the article in the Microsoft Knowledge Base:

Upgrade to OWA 2000

OWA 2000, which is available with Exchange 2000, has been redesigned to provide a more scalable, performance-oriented client. For more information about OWA 2000, visit the following Microsoft Web site: For more information about upgrading to Exchange 2000, click the following article number to view the article in the Microsoft Knowledge Base:

Front-End and Back-End Planning Considerations

You can distribute Exchange 2000 server tasks between front-end and back-end servers to balance tasks and to make the best use of available network resources, such as bandwidth. A front-end server responds to OWA client requests, and then works with back-end Exchange 2000 servers and Microsoft Active Directory directory service servers to retrieve the information that the client requested. If the OWA client has a fast connection to the front-end server, the client can download Web content from the front-end server while the front-end server proxies requests to the correct back-end server.

You can also configure the front-end server to authenticate users. Microsoft recommends that your network plan includes a domain controller near the front-end server to speed the authentication process.

NOTE: Exchange 2000 Enterprise Edition must be used on the front-end server.

For more information about how to configure front-end servers with Exchange 2000, click the following article number to view the article in the Microsoft Knowledge Base:

Use SSL

The use of Secure Sockets Layer (SSL) to encrypt OWA data while it is in transit has a small performance impact on the OWA server. Both the server and the client must complete additional processing to encrypt and decrypt the data.

NOTE: If your users gain access to OWA over a dial-up connection, the user's perceived performance is slower because the hardware compression that is used in most modem models cannot compress SSL traffic.

Some of the processing load can be relieved if you put the front-end server between your clients and the back-end Exchange 2000 servers. If you do so, the front-end server performs all of the SSL encryption and decryption processing.

You can also increase OWA performance if you add an SSL accelerator to your front-end and back-end topology. SSL accelerators generally come in two forms:

• Accelerator cards: Accelerator cards are typically used on the front-end server, and they offload the encryption and decryption overhead. This increases the throughput of each connection and reduces the work that the software on the server has to do.
• External accelerator devices: External accelerator devices sit between the clients and the front-end servers. Traffic that comes from the client is decrypted on the accelerator device, and then it is sent to the front-end server unencrypted. Likewise, traffic from the front-end server is sent to the accelerator device unencrypted, and then it is encrypted for transmission to the client.

NOTE: Make sure that the Microsoft Windows 2000 License Logging Service is running on the front-end server. Microsoft Internet Information Services (IIS) does not permit more than 10 simultaneous SSL connections unless this service is running.

For more information, click the following article number to view the article in the Microsoft Knowledge Base: