[This is preliminary documentation and subject to change]

Enabling Server-Side Includes

The Web server must detect that a file contains server-side include commands before processing the file. By default, the Web server is set up to process files with the .stm, .shtm, or .shtml file name extensions. You can disable the processing of server-side include directives for the entire Web server, for a Web site, for an application, or for an individual directory.

To enable server-side includes

Give files that contain SSI directives an SSI file name extension (.stm, .shtm, or .shtml).
You can add additional extensions; see Setting Application Mappings.
Put SSI files into a directory with Scripts or Execute access permissions. For more information, see Setting NTFS Permissions for a Directory or File.

To disable server-side includes

If the Web server receives a request for a page with the removed SSI file name extension, it will not process server-side include directives within the page.

In the IIS snap-in, select a Web site or directory, open its property sheets, and click the Home Directory or Directory tab. To disable SSI for an application, select the application starting point directory.
Click the Configuration button.
On the App Mappings tab, select the extension, and click Remove.