Post-Delivery Message Downgrading for Internationalized Email Messages
RFC 6857
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RFC - Proposed Standard
(March 2013; Errata)
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2015-10-14
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IETF
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Document shepherd |
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John Klensin
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Shepherd write-up |
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(last changed 2012-08-24)
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IESG state |
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RFC 6857 (Proposed Standard)
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Unknown
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Pete Resnick
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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
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