Post-Delivery Message Downgrading for Internationalized Email Messages
RFC 6857
Document | Type | RFC - Proposed Standard (March 2013; Errata) | |
---|---|---|---|
Author | Kazunori Fujiwara | ||
Last updated | 2020-01-21 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized with errata bibtex | ||
Reviews | |||
Stream | WG state | WG Document | |
Document shepherd | John Klensin | ||
Shepherd write-up | Show (last changed 2012-08-24) | ||
IESG | IESG state | RFC 6857 (Proposed Standard) | |
Action Holders |
(None)
|
||
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Pete Resnick | ||
Send notices to | (None) |
Internet Engineering Task Force (IETF) K. Fujiwara Request for Comments: 6857 JPRS Category: Standards Track March 2013 ISSN: 2070-1721 Post-Delivery Message Downgrading for Internationalized Email Messages Abstract The Email Address Internationalization (SMTPUTF8) extension to SMTP allows Unicode characters encoded in UTF-8 and outside the ASCII repertoire in mail header fields. Upgraded POP and IMAP servers support internationalized messages. If a POP or IMAP client does not support Email Address Internationalization, a POP or IMAP server cannot deliver internationalized messages to the client and cannot remove the message. To avoid that situation, this document describes a mechanism for converting internationalized messages into the traditional message format. As part of the conversion process, message elements that require internationalized treatment are recoded or removed, and receivers are able to recognize that they received messages containing such elements, even if they cannot process the internationalized elements. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6857. Fujiwara Standards Track [Page 1] RFC 6857 POP or IMAP Downgrade March 2013 Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Fujiwara Standards Track [Page 2] RFC 6857 POP or IMAP Downgrade March 2013 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 4 1.2. Possible Solutions . . . . . . . . . . . . . . . . . . . . 4 1.3. Approach Taken in This Specification . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Email Message Header Field Downgrading . . . . . . . . . . . . 7 3.1. Downgrading Method for Each ABNF Element . . . . . . . . . 7 3.1.1. Unstructured Downgrading . . . . . . . . . . . . . . . 7 3.1.2. Word Downgrading . . . . . . . . . . . . . . . . . . . 7 3.1.3. Comment Downgrading . . . . . . . . . . . . . . . . . 7 3.1.4. MIME-Value Downgrading . . . . . . . . . . . . . . . . 7 3.1.5. Display-Name Downgrading . . . . . . . . . . . . . . . 7 3.1.6. Domain Downgrading . . . . . . . . . . . . . . . . . . 8 3.1.7. Group Downgrading . . . . . . . . . . . . . . . . . . 8 3.1.8. Mailbox Downgrading . . . . . . . . . . . . . . . . . 8 3.1.9. Type-Addr Downgrading . . . . . . . . . . . . . . . . 9 3.1.10. Encapsulation: A Last Resort . . . . . . . . . . . . . 9 3.2. Downgrading Method for Each Header Field . . . . . . . . . 10 3.2.1. Address Header Fields That Contain <address> Elements . . . . . . . . . . . . . . . . . . . . . . . 10 3.2.2. Non-ASCII Strings in <comment> Elements . . . . . . . 11 3.2.3. Message-ID Header Fields . . . . . . . . . . . . . . . 11 3.2.4. Received Header Field . . . . . . . . . . . . . . . . 11 3.2.5. MIME Content Header Fields . . . . . . . . . . . . . . 12 3.2.6. Non-ASCII Characters in <unstructured> Elements . . . 12 3.2.7. Non-ASCII Characters in <phrase> Elements . . . . . . 12 3.2.8. Other Header Fields . . . . . . . . . . . . . . . . . 12 4. MIME Body Parts and Delivery Status Notifications . . . . . . 12 4.1. MIME Body Part Header Field Downgrading . . . . . . . . . 13 4.2. Delivery Status Notification Downgrading . . . . . . . . . 13Show full document text