Because Outlook Web Access runs on all the computers in an organization that are running Exchange 2007 SP1 that have the Client Access server role installed, you must deploy any customizations onto all the Client Access servers that the users connect to.

Note:
The customization features that are provided in Exchange 2007 SP1 are not available in Outlook Web Access Light.

When an Exchange-based application uses custom content classes that are stored in user mailboxes, the application must also seamlessly handle those custom content types inside Microsoft Office Outlook. Outlook supports custom forms for this purpose, and Exchange 2007 SP1 extends that support to Outlook Web Access.

A custom form for Outlook Web Access consists of custom .aspx pages that are stored on the Client Access server. An application that uses custom Outlook Web Access forms will typically have one .aspx page for each action that can be performed on the custom content type, such as create, send, reply, and so on.

Outlook Web Access in Exchange 2007 SP1 includes an XML file that is named the Custom Forms Registry. The default installation includes a template forms registry file that you can rename and then customize to fit the application. The forms registry file specifies how to handle custom content types by indicating what form to display when the user performs the actions that are indicated in the registry file.

To display a custom small icon for a content type, specify the icon file and content class in the SmallIconMapping section of the user interface customization file.

You can more closely integrate custom applications by using two Outlook Web Access user interface modifications in Exchange 2007 SP1.

To enhance the experience of users who are working with custom content classes, you can register new entries to the New drop-down menu. In this manner, you can enable users to create new items of a custom content class from Outlook Web Access.

To embed Web-based applications within the Outlook Web Access user interface, you can add entries to the navigation pane. This is useful when you want to provide access within Outlook Web access to applications that are loosely integrated with Exchange; for example, expense-tracking applications that store data outside the Exchange store.

You can use components of Outlook Web Access in your Web pages and applications by formulating URLs and then using the resulting HTML. For more information, see How to Use Outlook Web Access Web Parts.

In addition to integrating custom applications, you can also create custom themes for Outlook Web Access. Themes can be used to change colors, fonts, and images. For information about how to create custom themes, see How to Create a Theme for Outlook Web Access.