The MIME Content-Type header describes the content of the body-part. The Content-Type header format (with an example) is shown below:
Content-type: type/subtype; parameter=value; parameter=value...
type describes the type of content of the body part. Examples of type are Text, Multipart, Message, Application, Image, Audio, and Video.
subtype further describes content type. Each Content-type has its own set of subtypes. For examples: text/plain, application/octet-stream, and image/jpeg. Content Subtypes for MIME mail are assigned and listed by the IANA (Internet Assigned Numbers Authority). A copy of the list is at http://www.iana.org/assignments/media-types.
parameter is specific to Content-type/subtype pairs. For example, the charset and the name parameters are shown below:
Content-type: text/plain; charset=us-ascii Content-type: application/msword; name=temp.doc
The charset parameter specifies a character set for a textual message. The name parameter gives a suggested file name to be used if the data were to be written to a file.
Content-Type values, subtypes, and parameter names are case-insensitive.