By default, the server determines the MIME type by calling the type-by-extension function. This function instructs the server to look up the MIME type according to the requested resource’s file extension in the MIME types table. This table is created during virtual server initialization by the MIME types file (which is usually called mime.types). For more information, see Chapter 8, MIME Types.
For example, the entry in the MIME types table for the extensions .html and .htm is usually:
which indicates that all files with the extension .htm or .html are text files formatted as HTML, and the type is text/html.
If you make changes to the MIME types file, you must reconfigure the server for the changes to take effect.