Appendix F -- Summary of the Seven Content-types

Content-type: text

Subtypes defined by this document: plain

Important Parameters: charset

Encoding notes: quoted-printable generally preferred if an encoding is needed and the character set is mostly an ASCII superset.

Security considerations: Rich text formats such as TeX and Troff often contain mechanisms for executing arbitrary commands or file system operations, and should not be used automatically unless these security problems have been addressed. Even plain text may contain control characters that can be used to exploit the capabilities of "intelligent" terminals and cause security violations. User interfaces designed to run on such terminals should be aware of and try to prevent such problems.

Content-type: multipart

Subtypes defined by this document: mixed, alternative, digest, parallel.

Important Parameters: boundary

Encoding notes: No content-transfer-encoding is permitted.

Content-type: message

Subtypes defined by this document: rfc822, partial, external-body

Important Parameters: id, number, total, access-type, expiration, size, permission, name, site, directory, mode, server, subject

Encoding notes: No content-transfer-encoding is permitted. Specifically, only "7bit" is permitted for "message/partial" or "message/external-body", and only "7bit", "8bit", or "binary" are permitted for other subtypes of "message".

Content-type: application

Subtypes defined by this document: octet-stream, postscript

Important Parameters: type, padding
Deprecated Parameters: name and conversions were defined in RFC 1341.

Encoding notes: base64 preferred for unreadable subtypes.

Security considerations: This type is intended for the transmission of data to be interpreted by locally-installed programs. If used, for example, to transmit executable binary programs or programs in general-purpose interpreted languages, such as LISP programs or shell scripts, severe security problems could result. Authors of mail-reading agents are cautioned against giving their systems the power to execute mail-based application data without carefully considering the security implications. While it is certainly possible to define safe application formats and even safe interpreters for unsafe formats, each interpreter should be evaluated separately for possible security problems.

Content-type: image

Subtypes defined by this document: jpeg, gif

Important Parameters: none

Encoding notes: base64 generally preferred

Content-type: audio

Subtypes defined by this document: basic

Important Parameters: none

Encoding notes: base64 generally preferred

Content-type: video

Subtypes defined by this document: mpeg

Important Parameters: none

Encoding notes: base64 generally preferred