Plesk for Windows uses the IIS HTTP Server (http://www.iis.net/) for hosting and managing websites.
The default IIS configuration is defined by the hosting provider using IIS tools such as IIS Manager. The default configuration is applied to all websites on the server. However, a number of configuration parameters can be changed for individual websites right in the Plesk UI.
Website owners may need custom web server capabilities that are not provided by the default configuration. For example, unusual types of index files or the restricted access to the site by IP address.
You or site owners can configure web server settings for a website by specifying IIS settings in the Customer Panel. The custom website configuration overrides the default configuration. For details about custom IIS configuration, see Adjusting IIS Settings for Websites.