Internet Information Services (IIS) 6 Resource Kit

MIME Types

To reduce the available attack surface, IIS serves only a small number of default, static file types unless you approve an extension and that extension appears in the MIME types list. MIME types instruct a browser or mail application about how to handle the files received from a server. For example, when a browser requests an item on a server, the browser also requests the MIME type of the object. When IIS delivers a Web page to a client browser, IIS also sends the MIME type of the data it is sending. If there is an attached or embedded file in a specific format, then IIS also tells the client application the MIME type of the embedded or attached file. The client application then knows how to process or display the data being received ...