Before we discuss the types of customization, there are some things that you have to understand about Outlook Web Access.

First, Microsoft cannot support the system if you have modified the Outlook Web Access source files. We definitely support the unmodified system. But, if you have changed the underlying Web page source code, we cannot take responsibility for those changes. Therefore, the first thing to do when you are modifying the code is to make a backup copy of all the files you intend to modify. If you have trouble with your modifications, revert to the original files and see whether it works correctly then. For the official word on support for Outlook Web Access customization, make sure that you read Microsoft Knowledge Base article 327178, "Microsoft support policy for the customization of Outlook Web Access for Exchange."

Another important thing to remember is that Exchange service packs and software updates might overwrite your customized files. Two things that you should do to make sure that you can recover your changes are as follows:

• Make backups of the original files. Yes, this sounds obvious, but, in this instance, it is not for the usual reason. Before you modify any files, create a locally-stored copy of the original Outlook Web Access area. Store these files where they cannot be unintentionally accessed or deleted, for example in a compressed ZIP archive. After you install the service pack or software update, compare the contents of the archive with the files on disk. Very carefully examine the updated files to determine whether you must also update your customized files. It is much easier to compare the original file with an updated file than it is to compare a customized file against the updated file.
  
• Make backups of your customized files. Again, this sounds obvious. After you have deployed your customizations to a server, create a locally-stored copy of the customized Outlook Web Access area. Then, if you install a Service Pack or software update and there were no significant changes to Outlook Web Access, you can merely unpack the archived files.
  

And finally, remember that some customizations involve editing the Windows registry on the computer that is running Exchange Server. Be very careful when you make these changes, and always save the modified values to a .reg file, if you later have to reapply the changes.

One of the most straightforward--and common--Outlook Web Access customizations is modifying the text, images, and layout of the logon page.

The Active Server Pages (ASP) for logging on are stored in the Exchsvr\Exchweb\bin\auth\<language> directories. The ASP pages for logging off are located in the Exchsvr\Exchweb\bin\<language> directories. Remember that Outlook Web Access determines the appropriate language based on the user's browser settings. If you plan to customize these pages, make sure that you customize the pages for all the languages users might need.

Two implementation details make customizing the logon page fairly easy:

• All the text strings are defined as Jscript variables, located at the top of the logon.asp page.
  
• The images and page layout use standard HTML coding. This coding allows for easy manipulation.
  

For more in-depth information about how to customize the logon page, read Customizing the Outlook Web Access Logon Page.

Outlook Web Access lets you enable and disable individual features, and is also known as "segmentation". Features can be disabled on a per-server basis and on a per-user basis.

If a feature is disabled at the per-server level, that setting takes precedence over the value that is stored in the per-user settings. If a feature is enabled at the per-server level, the per-user settings, if they exist, control whether the user has access to the feature. The default per-user setting is to enable all features.

For complete instructions about how to configure Outlook Web Access segmentation, see the Microsoft Knowledge Base article 833340, "How to modify the appearance and the functionality of Outlook Web Access by using the segmentation feature in Exchange 2003."

Per-Server Segmentation

Per-server segmentation is controlled by using a Windows registry entry stored in the following registry key:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeWeb\OWA

The DWORD value DefaultMailboxFolderSet controls which features are available.

Caution:
Incorrectly editing the registry can cause serious problems that may require you to reinstall your operating system. Problems resulting from editing the registry incorrectly may not be able to be resolved. Before editing the registry, back up any valuable data.

Remember that the settings in the CurrentControlSet key are not made permanent until they are saved into a ControlSet000X key. This occurs when the system is shut down or restarted. You must be at least a local administrator to modify the registry on the Exchange server.

If the Exchange Server topology uses separate front-end and back-end servers, make the registry entry change on all the back-end servers.

Per-User Segmentation

Segmentation Bitmask Values

Although Outlook Web Access includes five standard themes, your organization might want a different look. By creating a new theme, or by modifying an existing theme, you can change the color scheme, background graphics, and button images.

Creating Outlook Web Access themes requires significant work, and so a full explanation is beyond the scope of this overview. However, full information is provided in Creating and Deploying Outlook Web Access Themes.

If the Exchange Server topology uses separate front-end and back-end servers, you have to change the Windows registry to add the theme on all the back-end servers, and you have to copy the theme files to the same location on each front-end server. If you use a clustered solution, make sure that you make the changes to each of the cluster nodes so that failover occurs correctly.

Microsoft Office SharePoint Portal Server 2003 includes four Web Parts that show you how to reuse Outlook Web Access in a portal application. The four Web Parts can display the contents of the user's Calendar, Inbox, Tasks, and a user-specified mailbox folder. For more information about the SharePoint Web Parts, see Integrating Exchange Server 2003 with SharePoint Products and Technologies.

In addition to changing how Outlook Web Access looks, you can also extend it to work with new types of items that are stored in Exchange. Use ASP-based Exchange Server Web forms to modify how items in the store are displayed and modified. You can find information about how to create custom Exchange Server Web forms on MSDN. For an overview of Exchange Server Web forms, see Web Forms. For more in-depth Web forms reference information, see Exchange Web Forms.

There have been Microsoft Knowledge Base articles and other sources that discuss how to use an Internet Services Application Programming Interface (ISAPI) filter to intercept calls to Outlook Web Access. Typical uses include modifying or restricting the information that is sent to Outlook Web Access. One example is Knowledge Base article 310599, "How t o h ard c ode the l anguage of OWA i nterface," which describes how to restrict the language that is used by the Outlook Web Access client.

However, we strongly recommend that you do not use an ISAPI filter together with Outlook Web Access.

For information about how to customize Outlook Web Access end-user options such as e-mail signatures, the number of items displayed, message tracking, and so on, see the Outlook Web Access Help documentation by clicking the Help icon in the upper-right corner of the Outlook Web Access user interface and selecting Options.