The HTTP Headers tab is another with important configurable properties. The option to Enable Content Expiration enables you to control how long your web pages are cached on client systems or proxy servers before the content is considered invalid. Although not enabled by default, consider enabling this setting and then select an expiry time consistent with how often you intend to change the content of your site.
This tab also allows you to configure custom HTTP headers. HTTP headers are used to support new HTTP features not supported in the current standard, such as new HTML tags, proxy server caching settings, and so forth. A great quick reference to HTTP headers can be found at http://www.cs.tut.fi/~jkorpela/http.html. The Content Rating section allows you to configure Recreational Software Advisory Council (RSAC) ratings for your site. Definitely consider configuring ratings for your site, since these ratings are used by content filtering software (such as NetNanny) and Web browsers to control the types of content that users (such as children) can access. Finally, the MIME Map section of this tab allows you to configure Multipurpose Internet Mail Extensions, a feature that IIS uses to provide Web browsers with information about the type of file they will be receiving. This section can be used to configure custom MIME types on your server, if necessary.
As its name suggests, the Custom Errors tab allows you to configure the messages that will be presented to the users when an error occurs, such as the “404” message associated with a Web page that does not exist or cannot be found. This tab allows you to change the settings of the built in error messages, and provides the path to the folder where the HTML documents associated with these messages are stored.