MIME version number MIME standards-track IETF (mailto:iesg@ietf.org) Internet Engineering Task Force RFC 2045 (section 4) An indicator that this message is formatted according to the MIME standard, and an indication of which version of MIME is utilized.

Identify content body part MIME standards-track IETF (mailto:iesg@ietf.org) Internet Engineering Task Force RFC 2045 (section 7) Specifies a Unique ID for one MIME body part of the content of a message.

Description of message body part MIME standards-track IETF (mailto:iesg@ietf.org) Internet Engineering Task Force RFC 2045 (section 8) Description of a particular body part of a message, for example a caption for an image body part.

Content transfer encoding applied MIME standards-track IETF (mailto:iesg@ietf.org) Internet Engineering Task Force RFC 2045 (section 6) Coding method used in a MIME message body part.

MIME content type MIME standards-track IETF (mailto:iesg@ietf.org) Internet Engineering Task Force RFC 2045 (section 5) Format of content (character set etc.) Note that the values for this header field are defined in different ways in RFC 1049 and in MIME (RFC 2045), look for the 'MIME-version' header field to understand if Content-Type is to be interpreted according to RFC 1049 or according to MIME. The MIME definition should be used in generating mail. RFC 1049 has 'historic' status. RFC 1766 defines a parameter 'difference' to this header field. Various other Content-Type define various additional parameters. For example, the parameter 'charset' is mandatory for all textual Content-Types. See also: RFC 1049, RFC 1123: 5.2.13, RFC 1766: 4.1.

Base to be used for resolving relative URIs within this content part. MIME standards-track IETF (mailto:iesg@ietf.org) Internet Engineering Task Force RFC 2110 Base to be used for resolving relative URIs within this content part. See also Content-Location. This header was included in the first version of MHTML and HTTP 1.1 but removed in the second version (RFC2557).

URI for retrieving a body part MIME standards-track IETF (mailto:iesg@ietf.org) Internet Engineering Task Force RFC 2557 URI using which the content of this body-part part was retrieved, might be retrievable, or which otherwise gives a globally unique identification of the content.

Indicates content features of a MIME body part MIME standards-track IETF (mailto:iesg@ietf.org) Internet Engineering Task Force RFC 2912 (section 3) The 'Content-features:' header can be used to annotate a MIME body part with a media feature expression, to indicate features of the body part content. See also: RFC 2533, RFC 2506, RFC 2045.

Intended content disposition and file name MIME standards-track IETF (mailto:iesg@ietf.org) Internet Engineering Task Force RFC 2183 Whether a MIME body part is to be shown inline or is an attachment; can also indicate a suggested filename for use when saving an attachment to a file.

Language of message content MIME standards-track IETF (mailto:iesg@ietf.org) Internet Engineering Task Force RFC 3282 Can include a code for the natural language used in a message, e.g. 'en' for English. Can also contain a list of languages for a message containing more than one language.

Alternative content available MIME work-in-progress IETF (mailto:iesg@ietf.org) Internet Engineering Task Force RFC 3297 Information about the media features of alternative content formats available for the current message.

MD5 checksum of content MIME standards-track IETF (mailto:iesg@ietf.org) Internet Engineering Task Force RFC 1864 Checksum of content to ensure that it has not been modified.

Time duration of content MIME standards-track IETF (mailto:iesg@ietf.org) Internet Engineering Task Force RFC 2424 Time duration of body part content, in seconds (e.g. for audio message).