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MIME (Multipurpose Internet Mail Extensions) Part Two: Message Header Extensions for Non-ASCII Text (RFC1522)

IP.com Disclosure Number: IPCOM000002353D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2000-Sep-12
Document File: 8 page(s) / 21K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

K. Moore: AUTHOR

Abstract

This memo describes an extension to the message format defined in RFC 1521 [1], to allow the representation of character sets other than ASCII in RFC 822 (STD 11) message headers. The extensions described were designed to be highly compatible with existing Internet mail handling software, and to be easily implemented in mail readers that support RFC 1521.

This text was extracted from a ASCII Text document.
This is the abbreviated version, containing approximately 14% of the total text.

Network Working Group K. Moore

Request for Comments: 1522 University of Tennessee

Obsoletes: 1342 September 1993

Category: Standards Track

MIME (Multipurpose Internet Mail Extensions) Part Two:

Message Header Extensions for Non-ASCII Text

Status of this Memo

This RFC specifies an Internet standards track protocol for the

Internet community, and requests discussion and suggestions for

improvements. Please refer to the current edition of the "Internet

Official Protocol Standards" for the standardization state and status

of this protocol. Distribution of this memo is unlimited.

Abstract

This memo describes an extension to the message format defined in RFC

1521 [1], to allow the representation of character sets other than

ASCII in RFC 822 (STD 11) message headers. The extensions described

were designed to be highly compatible with existing Internet mail

handling software, and to be easily implemented in mail readers that

support RFC 1521.

1. Introduction

RFC 1521 describes a mechanism for denoting textual body parts which

are coded in various character sets, as well as methods for encoding

such body parts as sequences of printable ASCII characters. This

memo describes similar techniques to allow the encoding of non-ASCII

text in various portions of a RFC 822 [2] message header, in a manner

which is unlikely to confuse existing message handling software.

Like the encoding techniques described in RFC 1521, the techniques

outlined here were designed to allow the use of non-ASCII characters

in message headers in a way which is unlikely to be disturbed by the

quirks of existing Internet mail handling programs. In particular,

some mail relaying programs are known to (a) delete some message

header fields while retaining others, (b) rearrange the order of

addresses in To or Cc fields, (c) rearrange the (vertical) order of

header fields, and/or (d) "wrap" message headers at different places

than those in the original message. In addition, some mail reading

programs are known to have difficulty correctly parsing message

headers which, while legal according to RFC 822, make use of

backslash-quoting to "hide" special characters such as "<", ",", or

":", or which exploit other infrequently-used features of that

specification.

While it is unfortunate that these programs do not correctly

interpret RFC 822 headers, to "break" these programs would cause

severe operational problems for the Internet mail system. The

extensions described in this memo therefore do not rely on little-

used features of RFC 822.

Instead, certain sequences of "ordinary" printable ASCII characters

(known as "encoded-words") are reserved for use as encoded data. The

syntax of encoded-words is such that they are unlikely to

"accidentally" appear as normal text in message headers.

Further...