What is a MIME type?

There are times when you would want the IIS web server to serve a file that has an extension that it does not recognize. That is, a file whose MIME type has not been defined. In such a case, IIS would return http error code, 404.3 as shown below.

HTTP Error 404.3 – Not Found
Description: The page you are requesting cannot be served because of the Multipurpose Internet Mail Extensions (MIME) map policy that is configured on the Web server. The page you requested has a file name extension that is not recognized, and therefore is not allowed.

MIME stands for Multi-purpose Internet Mail Extensions. MIME types form a standard way of classifying file types on the Internet. Internet programs such as Web servers and browsers all have a list of MIME types, so that they can transfer files of the same type in the same way, no matter what operating system they are working in.

A MIME type has two parts: a type and a subtype. They are separated by a slash (/). For example, the MIME type for Microsoft Word files is application and the subtype is msword. Together, the complete MIME type is application/msword.

Here is the list of available MIME types that you can add and configure on IIS

Hope this is useful.