Labeling data type

With MIME, data type can be specified in Content-Type:(CT:) field. The following is an example message whose body is US-ASCII text.

MIME-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Subject: hello
From: Kazu

Hi all,

If CT: is omitted, the content is treated as "Text/Plain; charset=us-ascii". And if CT: is "Text/Plain" and charset is not specified, its charset is considered as US-ASCII.

Likewise, if CT: is text, charset can be specified in the context of MIME. For Japanese, ISO-2022-JP is used.

MIME can embed multiple objects in its body, so called multipart. Each part in multipart consists of content-header and content-body. CT: appears in content-header as well as header. In the contrary, you can take header as a special type of content-header.

For more information, please refer to See section Multipart structure.

Important CT: is listed below.

`Text/Plain'

Text

`Message/Rfc822'

Message including MIME which has a header and a body

`Multipart/Mixed'

Multipart

`Application/Postscript'

PostScript

`Application/Octet-stream'

Binary stream. Can be considered as a binary file

`Image/Gif'

GIF

`Image/Jpeg'

JPEG

`Audio/Basic'

Audio file with AU format

`Video/Mpeg'

MPEG

`Message/External-body'

An phantom object whose real object exists outside of the message