Working with MIME Types (IIS 6.0)

Multipurpose Internet Mail Extensions (MIME) types instruct a Web browser or mail application how to handle files received from a server. For example, when a Web browser requests an item on a server, it also requests the MIME type of the object. Some MIME types, like graphics, can be displayed inside the browser. Others, such as word processing documents, require an external helper application to be displayed.

When IIS delivers a mail message to a mail application, or a Web page to a client Web browser, it also sends the MIME type of the data it is sending. If there is an attached or embedded file in a specific format, 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 from IIS.

IIS serves only files with known extensions registered in the MIME types list or with the operating system. IIS allows you to configure additional MIME types and change or remove MIME types. Removing a MIME type in IIS does not block access to that MIME type by other applications if it is also registered with the operating system.

IIS is preconfigured to recognize a default set of global MIME types. These MIME types are recognized by all Web sites you create in IIS. MIME types can also be defined at the Web site and directory levels, independent of one another or the types defined globally. When you view MIME types at the Web site or directory level, only the types unique to that level are displayed, not all types inherited from the next level up.


If you apply a MIME type at the global level after modifying the same MIME type at a lower level, the global-level MIME type overrides the modified MIME type at the lower level.


IIS returns a 404.3 error if a client request refers to a file name extension that is not defined in the MIME types.

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