This article explains how Microsoft Outlook renders Hypertext Markup Language (HTML) in various circumstances. If you are a solution developer, this information may help explain why custom HTML may not function as you expect.

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HTML is integrated into many features of Outlook, including:

•	Outlook Today
•	Custom Folder Home Pages
•	Web Views (Outlook Bar shortcuts and Web toolbar)
•	HTML mail messages

These features, and therefore HTML, play an increasing role in Outlook-based solutions.

Microsoft Internet Explorer must be installed with Microsoft Office, even if it is not used as the default browser. Microsoft Office applications, including Outlook, use Internet Explorer to render HTML in various parts of the applications. Microsoft Outlook does not contain any core code designed to render HTML. Instead, when HTML needs to be rendered, Outlook can use Internet Explorer in one of two ways:

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"Full" Internet Explorer. When Outlook uses the full version of Internet Explorer to display HTML, the general Internet security settings of Internet Explorer apply. To access these settings, double-click the Internet icon in Control Panel and then click either the Security or Advanced page of the window.

•

"Partial" Internet Explorer. Outlook can directly use the core portion of Internet Explorer that renders HTML, and therefore, bypass the typical security settings of Internet Explorer itself. The key advantage of using the subset of Internet Explorer is performance; HTML pages render faster. The disadvantage is that you cannot use the subset with certain HTML features such as frames and advanced table features.

When you are developing solutions using Outlook's HTML features, it is important to know how Outlook uses Internet Explorer to render the HTML page. This has a direct impact on any code or ActiveX components that you may want to use on the page. The following behaviors can be affected by whether Outlook uses full or partial Internet Explorer:

•	Performance
•	Ability to render "complex" HTML, such as tables and frames
•	How links are launched in new windows
•	How security is applied to the contents of HTML, including ActiveX controls and programming code.

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Outlook Today

Outlook Today uses the subset of Internet Explorer by default to achieve best performance. If you want to customize Outlook Today and require more complex HTML formatting, you may need to switch to the full version of Internet Explorer. The documentation for customizing the Outlook Today pages includes a section titled "Switch to the Full Version of Internet Explorer" that describes how to do this. For additional information about obtaining the documentation for customizing Outlook Today, click the following article number to view the article in the Microsoft Knowledge Base:

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Custom Folder Home Pages

Unlike Outlook Today, folder home pages for other folders use the full version of Internet Explorer by default. To change the folder setting so that Outlook uses the subset of Internet Explorer, you must use the Outlook object model to change the WebViewAllowNavigation property of the folder. This setting is not available in the Outlook user interface.

You can use the following two Visual Basic for Applications subroutines to change the setting for the folder that is currently selected:

Sub EnableFullIE()
   Set objFolder = Application.ActiveExplorer.CurrentFolder
   ' Enable full version of Internet Explorer for the current folder
   objFolder.WebViewAllowNavigation = True
   Set objFolder = Nothing
End Sub

Sub EnablePartialIE()
   Set objFolder = Application.ActiveExplorer.CurrentFolder
   ' Disable full version of Internet Explorer for the current folder
   objFolder.WebViewAllowNavigation = False
   Set objFolder = Nothing
End Sub

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Web Views (Outlook Bar Shortcuts)

Outlook 2000 allows you to create a shortcut on the Outlook Bar that points to a Web URL. When you click the icon, the Web page is displayed in the main Outlook window, much like a folder home page. However, the shortcut is not associated with a folder. Outlook uses the full version of Internet Explorer to render the HTML on these Web pages. This behavior cannot be changed.

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HTML Mail Messages

Microsoft Outlook allows you to send HTML as the body of a mail message. Outlook uses the full version of Internet Explorer to render this HTML. However, Outlook imposes additional levels of security to protect end users from potential HTML-based malicious code, or viruses. In addition, if the Outlook 2000 E-mail Security Update is applied, all HTML-based message active content is automatically disabled. For additional information about the Outlook security update, click the article number below to view the article in the Microsoft Knowledge Base: NOTE: HTML mail messages that are displayed in the Preview pane render less active content than if you were to open the item in a separate window. This is because of the design of the Preview pane.

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For additional information about available resources and answersto commonly asked questions about Microsoft Outlook 2000 solutions, click the article number below to view the article in the Microsoft Knowledge Base:

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