draft-ietf-eai-popimap-downgrade-06.txt   draft-ietf-eai-popimap-downgrade-07.txt 
Email Address Internationalization K. Fujiwara Email Address Internationalization K. Fujiwara
(EAI) JPRS (EAI) JPRS
Internet-Draft July 9, 2012 Internet-Draft July 31, 2012
Intended status: Standards Track Intended status: Standards Track
Expires: January 10, 2013 Expires: February 1, 2013
Post-delivery Message Downgrading for Internationalized Email Messages Post-delivery Message Downgrading for Internationalized Email Messages
draft-ietf-eai-popimap-downgrade-06.txt draft-ietf-eai-popimap-downgrade-07.txt
Abstract Abstract
The Email Address Internationalization (SMTPUTF8) extension allows The Email Address Internationalization (SMTPUTF8) extension to SMTP
UTF-8 characters in mail header fields. Upgraded POP and IMAP allows UTF-8 characters in mail header fields. Upgraded POP and IMAP
servers support internationalized Email messages. If a POP/IMAP servers support internationalized Email messages. If a POP/IMAP
client does not support Email Address Internationalization, POP/IMAP client does not support Email Address Internationalization, POP/IMAP
servers cannot send Internationalized Email Headers to the client and servers cannot deliver Internationalized Email Headers to the client
cannot remove the message. To avoid the situation, this document and cannot remove the message. To avoid the situation, this document
describes a conversion mechanism for internationalized Email messages describes a conversion mechanism for internationalized Email messages
to be in traditional message format. In the process, message to be in traditional message format. In the process, message
elements requiring internationalized treatment are recoded or removed elements requiring internationalized treatment are recoded or removed
and receivers are able to know that they received messages containing and receivers are able to know that they received messages containing
such elements even if they cannot treat the internationalized such elements even if they cannot process the internationalized
elements. elements.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 10, 2013. This Internet-Draft will expire on February 1, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 20 skipping to change at page 2, line 20
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Problem statement . . . . . . . . . . . . . . . . . . . . 4 1.1. Problem statement . . . . . . . . . . . . . . . . . . . . 4
1.2. Possible solutions . . . . . . . . . . . . . . . . . . . . 4 1.2. Possible solutions . . . . . . . . . . . . . . . . . . . . 4
1.3. Approach taken in this specification . . . . . . . . . . . 4 1.3. Approach taken in this specification . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. New Header Fields Definition . . . . . . . . . . . . . . . . . 6 3. Email Header Fields Downgrading . . . . . . . . . . . . . . . 6
4. Email Header Fields Downgrading . . . . . . . . . . . . . . . 6 3.1. Downgrading Method for Each ABNF Element . . . . . . . . . 6
4.1. Downgrading Method for Each ABNF Element . . . . . . . . . 7 3.1.1. <UNSTRUCTURED> Downgrading . . . . . . . . . . . . . . 6
4.1.1. <UNSTRUCTURED> Downgrading . . . . . . . . . . . . . . 7 3.1.2. <WORD> Downgrading . . . . . . . . . . . . . . . . . . 6
4.1.2. <WORD> Downgrading . . . . . . . . . . . . . . . . . . 7 3.1.3. <COMMENT> Downgrading . . . . . . . . . . . . . . . . 6
4.1.3. <COMMENT> Downgrading . . . . . . . . . . . . . . . . 7 3.1.4. <MIME-VALUE> Downgrading . . . . . . . . . . . . . . . 6
4.1.4. <MIME-VALUE> Downgrading . . . . . . . . . . . . . . . 7 3.1.5. <DISPLAY-NAME> Downgrading . . . . . . . . . . . . . . 7
4.1.5. <DISPLAY-NAME> Downgrading . . . . . . . . . . . . . . 7 3.1.6. <Domain> Downgrading . . . . . . . . . . . . . . . . . 7
4.1.6. <GROUP> Downgrading . . . . . . . . . . . . . . . . . 7 3.1.7. <GROUP> Downgrading . . . . . . . . . . . . . . . . . 7
4.1.7. <MAILBOX> Downgrading . . . . . . . . . . . . . . . . 8 3.1.8. <MAILBOX> Downgrading . . . . . . . . . . . . . . . . 7
4.1.8. ENCAPSULATION Downgrading . . . . . . . . . . . . . . 8 3.1.9. <TYPED-ADDRESS> Downgrading . . . . . . . . . . . . . 8
4.1.9. <TYPED-ADDRESS> Downgrading . . . . . . . . . . . . . 8 3.2. Downgrading Method for Each Header Field . . . . . . . . . 8
4.2. Downgrading Method for Each Header Field . . . . . . . . . 9 3.2.1. Address Header Fields That Contain <address>s . . . . 8
4.2.1. Address Header Fields That Contain <address>s . . . . 9 3.2.2. Address Header Fields with Typed Addresses . . . . . . 9
4.2.2. Address Header Fields with Typed Addresses . . . . . . 9 3.2.3. Downgrading Non-ASCII in Comments . . . . . . . . . . 9
4.2.3. Downgrading Non-ASCII in Comments . . . . . . . . . . 10 3.2.4. Message-ID Header Fields . . . . . . . . . . . . . . . 10
4.2.4. Message-ID Header Fields . . . . . . . . . . . . . . . 10 3.2.5. Received Header Field . . . . . . . . . . . . . . . . 10
4.2.5. Received Header Field . . . . . . . . . . . . . . . . 10 3.2.6. MIME Content Header Fields . . . . . . . . . . . . . . 10
4.2.6. MIME Content Header Fields . . . . . . . . . . . . . . 10 3.2.7. Non-ASCII in <unstructured> . . . . . . . . . . . . . 10
4.2.7. Non-ASCII in <unstructured> . . . . . . . . . . . . . 11 3.2.8. Non-ASCII in <phrase> . . . . . . . . . . . . . . . . 10
4.2.8. Non-ASCII in <phrase> . . . . . . . . . . . . . . . . 11 3.2.9. List- Header Fields and Other Header Fields . . . . . 11
4.2.9. Other Header Fields . . . . . . . . . . . . . . . . . 11 4. ENCAPSULATION: A Last Resort . . . . . . . . . . . . . . . . . 11
5. MIME Body-Part Header Field Downgrading . . . . . . . . . . . 11 5. MIME Body-Part Header Field Downgrading . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Implementation Notes . . . . . . . . . . . . . . . . . . . . . 13 7. Implementation Notes . . . . . . . . . . . . . . . . . . . . . 13
7.1. RFC 2047 Encoding . . . . . . . . . . . . . . . . . . . . 13 7.1. RFC 2047 Encoding . . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
10. Change History . . . . . . . . . . . . . . . . . . . . . . . . 14 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Version 00 . . . . . . . . . . . . . . . . . . . . . . . . 15 10.1. Normative References . . . . . . . . . . . . . . . . . . . 15
10.2. Version 01 . . . . . . . . . . . . . . . . . . . . . . . . 15 10.2. Informative References . . . . . . . . . . . . . . . . . . 17
10.3. Version 02 . . . . . . . . . . . . . . . . . . . . . . . . 15 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 17
10.4. Version 03 . . . . . . . . . . . . . . . . . . . . . . . . 15 A.1. Downgrading Example . . . . . . . . . . . . . . . . . . . 17
10.5. Version 04 . . . . . . . . . . . . . . . . . . . . . . . . 15 Appendix B. Change History . . . . . . . . . . . . . . . . . . . 19
10.6. Version 05 . . . . . . . . . . . . . . . . . . . . . . . . 16 B.1. Version 00 . . . . . . . . . . . . . . . . . . . . . . . . 19
10.7. Version 06 . . . . . . . . . . . . . . . . . . . . . . . . 16 B.2. Version 01 . . . . . . . . . . . . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 B.3. Version 02 . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . . 16 B.4. Version 03 . . . . . . . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . . 17 B.5. Version 04 . . . . . . . . . . . . . . . . . . . . . . . . 19
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 18 B.6. Version 05 . . . . . . . . . . . . . . . . . . . . . . . . 20
A.1. Downgrading Example . . . . . . . . . . . . . . . . . . . 18 B.7. Version 06 . . . . . . . . . . . . . . . . . . . . . . . . 20
B.8. Version 07 . . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction 1. Introduction
1.1. Problem statement 1.1. Problem statement
Traditional (legacy) mail systems, which are defined by [RFC5322], Traditional (legacy) mail systems, which are defined by [RFC5322] and
allow only ASCII characters in mail header field values. The other specifications, allow only ASCII characters in mail header
SMTPUTF8 extension ([RFC6530] and [RFC6532]) allow raw UTF-8 in those field values. The SMTPUTF8 extension ([RFC6530], [RFC6531] and
mail header fields. [RFC6532]) allow raw UTF-8 in those mail header fields.
If a header field contains non-ASCII strings, POP/IMAP servers cannot If a header field contains non-ASCII strings, POP/IMAP servers cannot
send Internationalized Email Headers to legacy clients and, because deliver Internationalized Email Headers to legacy clients and,
they have no obvious or standardized way to explain what is going on because they have no obvious or standardized way to explain what is
to those clients, cannot even safely discard the message. going on to those clients, cannot even safely discard the message.
1.2. Possible solutions 1.2. Possible solutions
There are four plausible approaches to the problem, with the There are four plausible approaches to the problem, with the
preferred one depending on the particular circumstances and preferred one depending on the particular circumstances and
relationship among the delivery SMTP server, the mail store, the POP relationship among the delivery SMTP server, the mail store, the POP
or IMAP server, and the users and their MUA clients: or IMAP server, and the users and their MUA clients:
1. If the delivery MTA has sufficient knowledge about the POP and/or 1. If the delivery MTA has sufficient knowledge about the POP and/or
IMAP servers and clients being used, the message may be rejected IMAP servers and clients being used, the message may be rejected
skipping to change at page 4, line 52 skipping to change at page 4, line 52
1.3. Approach taken in this specification 1.3. Approach taken in this specification
This specification describes the second of those options. It is This specification describes the second of those options. It is
worth noticing that, at least in the general case, none of these worth noticing that, at least in the general case, none of these
options preserve sufficient information to guarantee that it is options preserve sufficient information to guarantee that it is
possible to reply to an incoming message without loss of information, possible to reply to an incoming message without loss of information,
so the choice may be considered to be among "least bad" options. so the choice may be considered to be among "least bad" options.
This message downgrading mechanism converts mail header fields to an This message downgrading mechanism converts mail header fields to an
all-ASCII representation. The POP/IMAP servers can use the all-ASCII representation. The POP/IMAP servers can use the
downgrading mechanism and send the Internationalized Email message as downgrading mechanism and deliver the Internationalized Email message
a traditional form. Receivers can know they received some as a traditional form. Receivers can know they received some
internationalized messages or some unknown/broken messages. internationalized messages or some unknown/broken messages.
[RFC6532] allows UTF-8 characters to be used in mail header fields [RFC6532] allows UTF-8 characters to be used in mail header fields
and MIME header fields. The message downgrading mechanism specified and MIME header fields. [RFC6531] allows UTF-8 characters to be used
here describes the conversion method from the internationalized in some trace header fields. The message downgrading mechanism
messages that are defined in [RFC6530], and [RFC6532] to the specified here describes the conversion method from the
traditional email messages defined in [RFC5322]. internationalized messages that are defined in [RFC6530], and
[RFC6532] to the traditional email messages defined in [RFC5322].
This document provides a precise definition of the minimum- This document provides a precise definition of the minimum-
information-loss message downgrading process. information-loss message downgrading process.
Downgrading consists of the following three parts: Downgrading consists of the following three parts:
o New header field definitions o New header field definitions
o Email header field downgrading o Email header field downgrading
o MIME header field downgrading o MIME header field downgrading
In Section 3 of this document, header fields starting with Email header field downgrading is described in Section 3. It
generates ASCII-only header fields.
In Section 4 of this document, header fields starting with
"Downgraded-" are introduced. They preserve the information that "Downgraded-" are introduced. They preserve the information that
appeared in the original header fields. appeared in the original header fields.
Email header field downgrading is described in Section 4. It
generates ASCII-only header fields.
The definition of MIME header fields in Internationalized Email The definition of MIME header fields in Internationalized Email
Messages is described in [RFC6532]. MIME header field downgrading is Messages is described in [RFC6532]. MIME header field downgrading is
described in Section 5. It generates ASCII-only MIME header fields. described in Section 5. It generates ASCII-only MIME header fields.
Displaying downgraded messages that originally contained Displaying downgraded messages that originally contained
internationalized header fields is out of scope of this document. A internationalized header fields is out of scope of this document. A
POP/IMAP client which does not support UTF8 extension does not know POP/IMAP client which does not support UTF8 extensions as defined for
internationalized message format described in [RFC6532]. POP3 [UTF8 command] and IMAP ["ENABLE UTF8=ACCEPT" command] does not
know internationalized message format described in [RFC6532].
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
All specialized terms used in this specification are defined in the All specialized terms used in this specification are defined in the
Overview and Framework for Internationalized Email [RFC6530], in the Overview and Framework for Internationalized Email [RFC6530], in the
mail message specifications [RFC5322], or in the MIME documents mail message specifications [RFC5322], or in the MIME documents
[RFC2045] [RFC2047] [RFC2183] [RFC2231]. The terms "ASCII address",
"non-ASCII address", "SMTPUTF8", "message", "internationalized
message" are used with the definitions from [RFC6530]. The term
"non-ASCII string" is used with the definitions from [RFC6532].
3. New Header Fields Definition
New header fields are defined to preserve information that appeared
in non-ASCII strings in header fields of the incoming message. The
values of the new fields holds the original header field value in
encoded form. The revised header field syntax is specified as
follows:
fields =/ downgraded
downgraded = "Downgraded-Message-Id:" unstructured CRLF /
"Downgraded-Resent-Message-Id:" unstructured CRLF /
"Downgraded-In-Reply-To:" unstructured CRLF /
"Downgraded-References:" unstructured CRLF /
"Downgraded-Original-Recipient:" unstructured CRLF /
"Downgraded-Final-Recipient:" unstructured CRLF
To preserve a header field in a "Downgraded-" header field:
1. Generate a new header field.
* The field name is a concatenation of "Downgraded-" and the
original field name.
* The initial new field value is the original header field
value.
2. Treat the initial new header field value as if it were
unstructured, and then apply [RFC2047] encoding with charset
UTF-8 as necessary so that the resulting new header field value
is completely in ASCII.
3. Remove the original header field. [RFC2045] [RFC2047] [RFC2183] [RFC2231]. The terms "U-label",
"A-label" and "IDNA" are used with the definitions from [RFC5890].
The terms "ASCII address", "non-ASCII address", "SMTPUTF8",
"message", "internationalized message" are used with the definitions
from [RFC6530]. The term "non-ASCII string" is used with the
definitions from [RFC6532].
4. Email Header Fields Downgrading 3. Email Header Fields Downgrading
This section defines the conversion method to ASCII for each header This section defines the conversion method to ASCII for each header
field that may contain non-ASCII strings. field that may contain non-ASCII strings. Section 3.1 describes
rewriting methods for each ABNF element. Section 3.2 describes
[RFC6532] expands "Received:" header fields; [RFC5322] describes ABNF rewriting methods for each header field.
elements <mailbox>, <word>, <comment>, <unstructured>; [RFC2045]
describes ABNF element <value>.
4.1. Downgrading Method for Each ABNF Element 3.1. Downgrading Method for Each ABNF Element
Header field downgrading is defined below for each ABNF element. Header field downgrading is defined below for each ABNF element.
Converting the header field terminates when no non-ASCII strings Converting the header field terminates when no non-ASCII strings
remain in the header field. remain in the header field.
4.1.1. <UNSTRUCTURED> Downgrading [RFC5322] describes ABNF elements <group>, <mailbox>, <unstructured>,
<word>, <comment>, <display-name>. [RFC2045] describes ABNF element
<value>. <Domain> is updated to allow non-ASCII characters in Section
3.3 of [RFC6531] and Section 3.2 of [RFC6532].
3.1.1. <UNSTRUCTURED> Downgrading
If the header field has an <unstructured> field that contains non- If the header field has an <unstructured> field that contains non-
ASCII strings, apply [RFC2047] encoding with charset UTF-8. ASCII strings, apply [RFC2047] encoding with charset UTF-8.
4.1.2. <WORD> Downgrading 3.1.2. <WORD> Downgrading
If the header field has any <word> fields that contain non-ASCII If the header field has any <word> fields that contain non-ASCII
strings, apply [RFC2047] encoding with charset UTF-8. strings, apply [RFC2047] encoding with charset UTF-8.
4.1.3. <COMMENT> Downgrading 3.1.3. <COMMENT> Downgrading
If the header field has any <comment> fields that contain non-ASCII If the header field has any <comment> fields that contain non-ASCII
strings, apply [RFC2047] encoding with charset UTF-8. strings, apply [RFC2047] encoding with charset UTF-8.
4.1.4. <MIME-VALUE> Downgrading 3.1.4. <MIME-VALUE> Downgrading
If the header field has any <value> elements defined by [RFC2045] and If the header field has any <value> elements defined by [RFC2045] and
the elements contain non-ASCII strings, encode the <value> elements the elements contain non-ASCII strings, encode the <value> elements
according to [RFC2231] with charset UTF-8 and leave the language according to [RFC2231] with charset UTF-8 and leave the language
information empty. If the <value> element is <quoted-string> and it information empty. If the <value> element is <quoted-string> and it
contains <CFWS> outside the DQUOTE, remove the <CFWS> before this contains <CFWS> outside the DQUOTE, remove the <CFWS> before this
conversion. conversion.
4.1.5. <DISPLAY-NAME> Downgrading 3.1.5. <DISPLAY-NAME> Downgrading
If the header field has any <address> (<mailbox> or <group>) elements If the header field has any <address> (<mailbox> or <group>) elements
and they have <display-name> elements that contain non-ASCII strings, and they have <display-name> elements that contain non-ASCII strings,
encode the <display-name> elements according to [RFC2047] with encode the <display-name> elements according to [RFC2047] with
charset UTF-8. DISPLAY-NAME downgrading is the same algorithm as charset UTF-8. DISPLAY-NAME downgrading is the same algorithm as
WORD downgrading. WORD downgrading.
4.1.6. <GROUP> Downgrading 3.1.6. <Domain> Downgrading
If the header field has any <Domain> elements that contain U-labels,
rewrite the non-ASCII domain name into ASCII domain name using
A-labels as specified in IDNA [RFC5891].
3.1.7. <GROUP> Downgrading
<group> is defined in Section 3.4 of [RFC5322]. The <group> elements <group> is defined in Section 3.4 of [RFC5322]. The <group> elements
may contain <mailbox>s which contain non-ASCII addresses. may contain <mailbox>es which contain non-ASCII addresses.
If the header field has any <group> elements that contain <mailbox> If the header field has any <group> elements that contain <mailbox>
elements, and those <mailbox> elements in turn contain non-ASCII elements and one of <mailbox>es contains a non-ASCII <local-part>,
addresses, rewrite each <group> element as rewrite each <group> element as
display-name ENCODED_WORD " :;" display-name ENCODED_WORD " :;"
where the <ENCODED_WORD> is the original <group-list> encoded where the <ENCODED_WORD> is the original <group-list> encoded
according to [RFC2047]. according to [RFC2047].
4.1.7. <MAILBOX> Downgrading Otherwise, the header field does not contain non-ASCII <local-part>.
If the header field contain non-ASCII <mailbox>es, they contain non-
ASCII domain names. Rewrite the non-ASCII domain names into ASCII
domain names using A-labels as specified in IDNA [RFC5891].
Generated <mailbox>es contain ASCII addresses only.
The <mailbox> elements have no equivalent format for non-ASCII 3.1.8. <MAILBOX> Downgrading
addresses. If the header field has any <mailbox> elements that
contain non-ASCII strings in their <addr-spec> element, rewrite each If the <local-part> of the <mailbox> element does not contain non-
<addr-spec> element to ASCII-only format. The <addr-spec> element ASCII characters, the <domain> element contains non-ASCII characters.
that contains non-ASCII strings may appear in two forms as: Rewrite the non-ASCII domain name into ASCII domain name using
A-labels as specified in IDNA [RFC5891].
Otherwise, the <local-part> contains non-ASCII characters. The non-
ASCII <local-part> has no equivalent format for ASCII addresses.
Rewrite each <addr-spec> element to ASCII-only group format following
the model above. The <addr-spec> element that contains non-ASCII
strings may appear in two forms as:
"<" addr-spec ">" "<" addr-spec ">"
addr-spec addr-spec
Rewrite both as: Rewrite both as:
ENCODED-WORD " :;" ENCODED-WORD " :;"
where the <ENCODED-WORD> is the original <addr-spec> encoded where the <ENCODED-WORD> is the original <addr-spec> encoded
according to [RFC2047]. according to [RFC2047].
4.1.8. ENCAPSULATION Downgrading 3.1.9. <TYPED-ADDRESS> Downgrading
Encapsulate the header field in a "Downgraded-" header field as
described in Section 3 as a last resort.
Applying this procedure to "Received:" header field is prohibited.
ENCAPSULATION Downgrading is allowed for "Message-ID",
"In-Reply-To:", "References:", "Original-Recipient" and "Final-
Recipient" header fields.
4.1.9. <TYPED-ADDRESS> Downgrading
If the header field contains <utf-8-type-addr> and the <utf-8-type- If the header field contains <utf-8-type-addr> and the <utf-8-type-
addr> contains raw non-ASCII strings, it is in utf-8-address form. addr> contains raw non-ASCII strings, it is in utf-8-address form.
Convert it to utf-8-addr-xtext form. Those forms are described in Convert it to utf-8-addr-xtext form. Those forms are described in
[RFC6533]. COMMENT downgrading is also performed in this case. If [RFC6533]. COMMENT downgrading is also performed in this case. If
the address type is unrecognized and the header field contains non- the address type is unrecognized and the header field contains non-
ASCII strings, then fall back to using ENCAPSULATION downgrading on ASCII strings, then fall back to using ENCAPSULATION on the entire
the entire header field. header field specified in Section 4.
4.2. Downgrading Method for Each Header Field 3.2. Downgrading Method for Each Header Field
[RFC4021] establishes a registry of header fields. This section [RFC4021] establishes a registry of header fields. This section
describes the downgrading method for each header field. describes the downgrading method for each header field.
If the whole mail header field does not contain non-ASCII strings, If the whole mail header field does not contain non-ASCII strings,
email header field downgrading is not required. Each header field's email header field downgrading is not required. Each header field's
downgrading method is described below. downgrading method is described below.
4.2.1. Address Header Fields That Contain <address>s 3.2.1. Address Header Fields That Contain <address>s
From: From:
Sender: Sender:
To: To:
Cc: Cc:
Bcc: Bcc:
Reply-To: Reply-To:
Resent-From: Resent-From:
Resent-Sender: Resent-Sender:
Resent-To: Resent-To:
skipping to change at page 9, line 25 skipping to change at page 9, line 4
From: From:
Sender: Sender:
To: To:
Cc: Cc:
Bcc: Bcc:
Reply-To: Reply-To:
Resent-From: Resent-From:
Resent-Sender: Resent-Sender:
Resent-To: Resent-To:
Resent-Cc: Resent-Cc:
Resent-Bcc: Resent-Bcc:
Resent-Reply-To: Resent-Reply-To:
Return-Path: Return-Path:
Disposition-Notification-To: Disposition-Notification-To:
If the header field contains <group> elements that contain non-ASCII If the header field contains <group> elements that contain non-ASCII
addresses, perform <COMMENT> downgrading, <DISPLAY-NAME> downgrading, addresses, perform <COMMENT> downgrading, <DISPLAY-NAME> downgrading,
and <GROUP> downgrading. and <GROUP> downgrading as described in the corresponding subsections
of Section 3.1. Optionally add those words where appropriate to the
next paragraph, but I think once will make it clear.
If the header field contains <mailbox> elements that contain non- If the header field contains <mailbox> elements that contain non-
ASCII addresses, perform <COMMENT> downgrading, <DISPLAY-NAME> ASCII addresses, perform <COMMENT> downgrading, <DISPLAY-NAME>
downgrading, and <MAILBOX> downgrading. downgrading, and <MAILBOX> downgrading.
This procedure may generate empty <group> elements in "From:", This procedure may generate empty <group> elements in "From:",
"Sender:" and "Reply-To:" header fields. "Sender:" and "Reply-To:" header fields.
[I-D.leiba-5322upd-from-group] updates [RFC5322] to allow (empty) [I-D.leiba-5322upd-from-group] updates [RFC5322] to allow (empty)
<group> elements in "From:", "Sender:" and "Reply-To:" header fields. <group> elements in "From:", "Sender:" and "Reply-To:" header fields.
4.2.2. Address Header Fields with Typed Addresses 3.2.2. Address Header Fields with Typed Addresses
Original-Recipient: Original-Recipient:
Final-Recipient: Final-Recipient:
If the header field contains non-ASCII strings, perform <TYPED- If the header field contains non-ASCII strings, perform <TYPED-
ADDRESS> downgrading. ADDRESS> downgrading.
4.2.3. Downgrading Non-ASCII in Comments 3.2.3. Downgrading Non-ASCII in Comments
Date: Date:
Resent-Date: Resent-Date:
MIME-Version: MIME-Version:
Content-ID: Content-ID:
Content-Transfer-Encoding: Content-Transfer-Encoding:
Content-Language: Content-Language:
Accept-Language: Accept-Language:
Auto-Submitted: Auto-Submitted:
These header fields do not contain non-ASCII strings except in These header fields do not contain non-ASCII strings except in
comments. If the header field contains UTF-8 characters in comments, comments. If the header field contains UTF-8 characters in comments,
perform <COMMENT> downgrading. perform <COMMENT> downgrading.
4.2.4. Message-ID Header Fields 3.2.4. Message-ID Header Fields
Message-ID: Message-ID:
Resent-Message-ID: Resent-Message-ID:
In-Reply-To: In-Reply-To:
References: References:
Perform ENCAPSULATION Downgrading. Perform ENCAPSULATION as specified in Section 4.
4.2.5. Received Header Field 3.2.5. Received Header Field
Received: Received:
If the FOR clause contains a non-ASCII address, remove the FOR clause If <Domain> elements or <Mailbox> elements contains U-labels, perform
from the header field. Comments may contain non-ASCII strings, <Domain> downgrading specified in Section 3.1.6. Comments may
Perform <COMMENT> downgrading. Other parts should not contain non- contain non-ASCII strings, perform <COMMENT> downgrading.
ASCII strings.
After the <Domain> downgrading and the <COMMENT> downgrading, if the
FOR clause contains a non-ASCII <local-part>, remove the "FOR"
clause. If the ID clause contains a non-ASCII values, remove the
"ID" clause.
3.2.6. MIME Content Header Fields
4.2.6. MIME Content Header Fields
Content-Type: Content-Type:
Content-Disposition: Content-Disposition:
Perform <MIME-VALUE> downgrading and <COMMENT> downgrading. Perform <MIME-VALUE> downgrading and <COMMENT> downgrading.
4.2.7. Non-ASCII in <unstructured> 3.2.7. Non-ASCII in <unstructured>
Subject: Subject:
Comments: Comments:
Content-Description: Content-Description:
Perform <UNSTRUCTURED> downgrading. Perform <UNSTRUCTURED> downgrading.
4.2.8. Non-ASCII in <phrase> 3.2.8. Non-ASCII in <phrase>
Keywords: Keywords:
Perform <WORD> downgrading. Perform <WORD> downgrading.
4.2.9. Other Header Fields 3.2.9. List- Header Fields and Other Header Fields
There are other header fields that contain non-ASCII strings. They There are other header fields that contain non-ASCII strings. They
are user-defined and missing from this document, or future defined are user-defined and missing from this document, or future defined
header fields. They are treated as "Optional Fields" and their field header fields. They are treated as "Optional Fields" and their field
values are treated as unstructured described in Section 3.6.8 of values are treated as unstructured described in Section 3.6.8 of
[RFC5322]. [RFC5322].
Perform <UNSTRUCTURED> downgrading. Perform <UNSTRUCTURED> downgrading.
If the software understands the header field's structure and a If the software understands the header field's structure and a
downgrading algorithm other than UNSTRUCTURED is applicable, that downgrading algorithm other than UNSTRUCTURED is applicable, that
software SHOULD use that algorithm; UNSTRUCTURED downgrading is used software SHOULD use that algorithm; UNSTRUCTURED downgrading is used
as a last resort. as a last resort.
Mailing list header fields (those that start in "List-") are part of Mailing list header fields (those that start in "List-") are part of
this category. this category.
4. ENCAPSULATION: A Last Resort
As a last resort when header fields cannot be converted as discussed
in the previous section, the fields are deleted and replaced by
specialized new header fields. Those fields are defined to preserve,
in encoded form, as much information as possible from the header
field values of the incoming message. The syntax of these new header
fields is:
fields =/ downgraded
downgraded = "Downgraded-Message-Id:" unstructured CRLF /
"Downgraded-Resent-Message-Id:" unstructured CRLF /
"Downgraded-In-Reply-To:" unstructured CRLF /
"Downgraded-References:" unstructured CRLF /
"Downgraded-Original-Recipient:" unstructured CRLF /
"Downgraded-Final-Recipient:" unstructured CRLF
Applying this procedure to "Received:" header field is prohibited.
ENCAPSULATION Downgrading is allowed for "Message-ID",
"In-Reply-To:", "References:", "Original-Recipient" and "Final-
Recipient" header fields.
To preserve a header field in a "Downgraded-" header field:
1. Generate a new header field.
* The field name is a concatenation of "Downgraded-" and the
original field name.
* The initial new field value is the original header field
value.
2. Treat the initial new header field value as if it were
unstructured, and then apply [RFC2047] encoding with charset
UTF-8 as necessary so that the resulting new header field value
is completely in ASCII.
3. Remove the original header field.
5. MIME Body-Part Header Field Downgrading 5. MIME Body-Part Header Field Downgrading
MIME body-part header fields may contain non-ASCII strings [RFC6532]. MIME body-part header fields may contain non-ASCII strings [RFC6532].
This section defines the conversion method to ASCII-only header This section defines the conversion method to ASCII-only header
fields for each MIME header field that contains non-ASCII strings. fields for each MIME header field that contains non-ASCII strings.
Parse the message body's MIME structure at all levels and check each Parse the message body's MIME structure at all levels and check each
MIME header field to see whether it contains non-ASCII strings. If MIME header field to see whether it contains non-ASCII strings. If
the header field contains non-ASCII strings in the header field the header field contains non-ASCII strings in the header field
value, the header field is a target of the MIME body-part header value, the header field is a target of the MIME body-part header
field's downgrading. Each MIME header field's downgrading method is field's downgrading. Each MIME header field's downgrading method is
described below. COMMENT downgrading, MIME-VALUE downgrading, and described below. COMMENT downgrading, MIME-VALUE downgrading, and
UNSTRUCTURED downgrading are described in Section 4. UNSTRUCTURED downgrading are described in Section 3.
Content-ID: Content-ID:
The "Content-ID:" header field does not contain non-ASCII strings The "Content-ID:" header field does not contain non-ASCII strings
except in comments. If the header field contains UTF-8 characters except in comments. If the header field contains UTF-8 characters
in comments, perform <COMMENT> downgrading. in comments, perform <COMMENT> downgrading.
Content-Type: Content-Type:
Content-Disposition: Content-Disposition:
Perform <MIME-VALUE> downgrading and <COMMENT> downgrading. Perform <MIME-VALUE> downgrading and <COMMENT> downgrading.
skipping to change at page 12, line 40 skipping to change at page 13, line 16
But they still contain MIME-encapsulated header fields that contain But they still contain MIME-encapsulated header fields that contain
non-ASCII strings. Furthermore, the body part may contain UTF-8 non-ASCII strings. Furthermore, the body part may contain UTF-8
characters. Implementations parsing Internet messages need to accept characters. Implementations parsing Internet messages need to accept
UTF-8 body parts and UTF-8 header fields that are MIME-encoded. UTF-8 body parts and UTF-8 header fields that are MIME-encoded.
Thus, this document inherits the security considerations of MIME- Thus, this document inherits the security considerations of MIME-
encoded header fields ([RFC2047] and [RFC3629]). encoded header fields ([RFC2047] and [RFC3629]).
Rewriting header fields increases the opportunities for undetected Rewriting header fields increases the opportunities for undetected
spoofing by malicious senders. However, the rewritten header field spoofing by malicious senders. However, the rewritten header field
values are preserved in equivalent MIME form or in newly defined values are preserved in equivalent MIME form or in newly defined
header fields which traditional MUAs do not care. header fields for which traditional MUAs have no special processing
procedures.
The techniques described here invalidate methods that depend on The techniques described here invalidate methods that depend on
digital signatures over any part of the message, which includes the digital signatures over any part of the message, which includes the
top-level header fields and body-part header fields. Depending on top-level header fields and body-part header fields. Depending on
the specific message being downgraded, at least the following the specific message being downgraded, at least the following
techniques are likely to break: DomainKeys Identified Mail (DKIM), techniques are likely to break: DomainKeys Identified Mail (DKIM),
and possibly S/MIME and Pretty Good Privacy (PGP). Receivers may and possibly S/MIME and Pretty Good Privacy (PGP). Receivers may
know they need to update their MUAs, or they don't care. know they need to update their MUAs, or they don't care.
While information in any email header field should usually be treated While information in any email header field should usually be treated
with some suspicion, current email systems commonly employ various with some suspicion, current email systems commonly employ various
mechanisms and protocols to make the information more trustworthy. mechanisms and protocols to make the information more trustworthy.
Information in the new Downgraded-* header fields is not inspected by Information in the new Downgraded-* header fields is not inspected by
MUAs, and may be even less trustworthy than the traditional header traditional MUAs, and may be even less trustworthy than the
fields. Note that the Downgraded-* header fields could have been traditional header fields. Note that the Downgraded-* header fields
inserted with malicious intent (and with content unrelated to the could have been inserted with malicious intent (and with content
traditional header fields), however traditional MUAs do not parse unrelated to the traditional header fields), however traditional MUAs
Downgraded-* header fields. do not parse Downgraded-* header fields.
In addition, if an Authentication-Results header field [RFC5451] is In addition, if an Authentication-Results header field [RFC5451] is
present, traditional MUAs may treat that the digital signatures are present, traditional MUAs may treat that the digital signatures are
valid. valid.
See the "Security Considerations" section in See the "Security Considerations" section in
[I-D.leiba-5322upd-from-group] and [RFC6530] for more discussion. [I-D.leiba-5322upd-from-group] and [RFC6530] for more discussion.
7. Implementation Notes 7. Implementation Notes
skipping to change at page 14, line 9 skipping to change at page 14, line 30
does not use all "Downgraded-" header fields registered by [RFC5504]. does not use all "Downgraded-" header fields registered by [RFC5504].
The following header fields should be registered in the Permanent The following header fields should be registered in the Permanent
Message Header Field registry, in accordance with the procedures set Message Header Field registry, in accordance with the procedures set
out in [RFC3864]. out in [RFC3864].
Header field name: Downgraded-Message-Id Header field name: Downgraded-Message-Id
Applicable protocol: mail Applicable protocol: mail
Status: standard Status: standard
Author/change controller: IETF Author/change controller: IETF
Specification document(s): This document (Section 3) Specification document(s): This document (Section 4)
Header field name: Downgraded-In-Reply-To Header field name: Downgraded-In-Reply-To
Applicable protocol: mail Applicable protocol: mail
Status: standard Status: standard
Author/change controller: IETF Author/change controller: IETF
Specification document(s): This document (Section 3) Specification document(s): This document (Section 4)
Header field name: Downgraded-References Header field name: Downgraded-References
Applicable protocol: mail Applicable protocol: mail
Status: standard Status: standard
Author/change controller: IETF Author/change controller: IETF
Specification document(s): This document (Section 3) Specification document(s): This document (Section 4)
Header field name: Downgraded-Original-Recipient Header field name: Downgraded-Original-Recipient
Applicable protocol: mail Applicable protocol: mail
Status: standard Status: standard
Author/change controller: IETF Author/change controller: IETF
Specification document(s): This document (Section 3) Specification document(s): This document (Section 4)
Header field name: Downgraded-Final-Recipient Header field name: Downgraded-Final-Recipient
Applicable protocol: mail Applicable protocol: mail
Status: standard Status: standard
Author/change controller: IETF Author/change controller: IETF
Specification document(s): This document (Section 3) Specification document(s): This document (Section 4)
9. Acknowledgements 9. Acknowledgements
This document draws heavily from the experimental in-transit message This document draws heavily from the experimental in-transit message
downgrading procedure described in RFC 5504 [RFC5504]. The downgrading procedure described in RFC 5504 [RFC5504]. The
contribution of the co-author of that earlier document, Y. Yoneya, contribution of the co-author of that earlier document, Y. Yoneya,
are gratefully acknowledged. Significant comments and suggestions are gratefully acknowledged. Significant comments and suggestions
were received from John Klensin, Barry Leiba, Randall Gellens, Pete were received from John Klensin, Barry Leiba, Randall Gellens, Pete
Resnick, Martin J. Durst, and other WG participants. Resnick, Martin J. Durst, and other WG participants.
10. Change History 10. References
[[RFC Editor: Please remove this section prior to publication.]]
This section is used for tracking the update of this document. Will
be removed after finalize.
10.1. Version 00
o Initial version
o Imported header field downgrading from RFC 5504
10.2. Version 01
o same as Version 00
10.3. Version 02
o Added updating RFC 5322 to allow <group> syntax in From: and
Sender
o Added GROUP Downgrading
10.4. Version 03
o Replaced <utf8-addr-spec> with <addr-spec>
o Added updating RFC 5322 to allow <group> syntax in From: and
Sender
o Added one sentence in Security considerations
o Updated IANA considerations
10.5. Version 04
o Removed "Internationalized Address removed" from GROUP and MAILBOX
downgrading
o Updated "Updating RFC 5322"
o Compacted new header field definition
o Compacted security considerations
o Updated IANA considerations to remove obsoleting header fields
that are registered by RFC 5504
o Added a discussion of alternate downgrading models for the POP and
IMAP cases.
o Incorporated a large number of editorial changes to improve
clarity.
10.6. Version 05
o Some text corrections
o Terminology change: only to use non-ASCII address, non-ASCII
message, non-ASCII string and imported them from RFC 6530 and RFC
6532
o Replace "non-ASCII character" with "non-ASCII string"
o Removed 5.1.1. RECEIVED Downgrading: It's
10.7. Version 06
o Removed "Updating RFC 5322"
o Added reference to draft-leiba-5322upd-from-group
11. References
11.1. Normative References 10.1. Normative References
[RFC2045] Freed, N. and N. Borenstein, [RFC2045] Freed, N. and N. Borenstein,
"Multipurpose Internet Mail "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Extensions (MIME) Part One: Format of
Internet Message Bodies", RFC 2045, Internet Message Bodies", RFC 2045,
November 1996. November 1996.
[RFC2047] Moore, K., "MIME (Multipurpose [RFC2047] Moore, K., "MIME (Multipurpose
Internet Mail Extensions) Part Three: Internet Mail Extensions) Part Three:
Message Header Extensions for Non- Message Header Extensions for Non-
skipping to change at page 17, line 21 skipping to change at page 16, line 21
Message Header Fields", BCP 90, Message Header Fields", BCP 90,
RFC 3864, September 2004. RFC 3864, September 2004.
[RFC4021] Klyne, G. and J. Palme, "Registration [RFC4021] Klyne, G. and J. Palme, "Registration
of Mail and MIME Header Fields", of Mail and MIME Header Fields",
RFC 4021, March 2005. RFC 4021, March 2005.
[RFC5322] Resnick, P., Ed., "Internet Message [RFC5322] Resnick, P., Ed., "Internet Message
Format", RFC 5322, October 2008. Format", RFC 5322, October 2008.
[RFC5890] Klensin, J., "Internationalized
Domain Names for Applications (IDNA):
Definitions and Document Framework",
RFC 5890, August 2010.
[RFC5891] Klensin, J., "Internationalized
Domain Names in Applications (IDNA):
Protocol", RFC 5891, August 2010.
[RFC6530] Klensin, J. and Y. Ko, "Overview and [RFC6530] Klensin, J. and Y. Ko, "Overview and
Framework for Internationalized Framework for Internationalized
Email", RFC 6530, February 2012. Email", RFC 6530, February 2012.
[RFC6531] Yao, J. and W. Mao, "SMTP Extension
for Internationalized Email",
RFC 6531, February 2012.
[RFC6532] Yang, A., Steele, S., and N. Freed, [RFC6532] Yang, A., Steele, S., and N. Freed,
"Internationalized Email Headers", "Internationalized Email Headers",
RFC 6532, February 2012. RFC 6532, February 2012.
[RFC6533] Hansen, T., Newman, C., and A. [RFC6533] Hansen, T., Newman, C., and A.
Melnikov, "Internationalized Delivery Melnikov, "Internationalized Delivery
Status and Disposition Status and Disposition
Notifications", RFC 6533, Notifications", RFC 6533,
February 2012. February 2012.
[I-D.leiba-5322upd-from-group] Leiba, B., "Update to Internet [I-D.leiba-5322upd-from-group] Leiba, B., "Update to Internet
Message Format to Allow Group Syntax Message Format to Allow Group Syntax
in the 'From:' Header Field", in the 'From:' Header Field",
draft-leiba-5322upd-from-group-01 draft-leiba-5322upd-from-group-03
(work in progress), July 2012. (work in progress), July 2012.
11.2. Informative References 10.2. Informative References
[RFC5451] Kucherawy, M., "Message Header Field [RFC5451] Kucherawy, M., "Message Header Field
for Indicating Message Authentication for Indicating Message Authentication
Status", RFC 5451, April 2009. Status", RFC 5451, April 2009.
[RFC5504] Fujiwara, K. and Y. Yoneya, [RFC5504] Fujiwara, K. and Y. Yoneya,
"Downgrading Mechanism for Email "Downgrading Mechanism for Email
Address Internationalization", Address Internationalization",
RFC 5504, March 2009. RFC 5504, March 2009.
skipping to change at page 19, line 13 skipping to change at page 18, line 13
non-ASCII strings. non-ASCII strings.
Return-Path: <NON-ASCII-LOCAL@example.com> Return-Path: <NON-ASCII-LOCAL@example.com>
Received: from ... by ... for <NON-ASCII-REMOTE1@example.net> Received: from ... by ... for <NON-ASCII-REMOTE1@example.net>
Received: from ... by ... for <NON-ASCII-REMOTE1@example.net> Received: from ... by ... for <NON-ASCII-REMOTE1@example.net>
From: DISPLAY-LOCAL <NON-ASCII-LOCAL@example.com> From: DISPLAY-LOCAL <NON-ASCII-LOCAL@example.com>
To: DISPLAY-REMOTE1 <NON-ASCII-REMOTE1@example.net>, To: DISPLAY-REMOTE1 <NON-ASCII-REMOTE1@example.net>,
DISPLAY-REMOTE2 <NON-ASCII-REMOTE2@example.com> DISPLAY-REMOTE2 <NON-ASCII-REMOTE2@example.com>
Cc: DISPLAY-REMOTE3 <NON-ASCII-REMOTE3@example.org> Cc: DISPLAY-REMOTE3 <NON-ASCII-REMOTE3@example.org>
Subject: NON-ASCII-SUBJECT Subject: NON-ASCII-SUBJECT
Date: DATE Date: Mon, 30 Jul 2012 01:23:45 -0000
Message-Id: NON-ASCII-MESSAGE_ID Message-Id: NON-ASCII-MESSAGE_ID
Mime-Version: 1.0 Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8" Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit Content-Transfer-Encoding: 8bit
X-Unknown-Header: NON-ASCII-CHARACTERS X-Unknown-Header: NON-ASCII-CHARACTERS
MAIL_BODY MAIL_BODY
Figure 1: Received message in a mail drop Figure 1: Received message in a mail drop
skipping to change at page 19, line 42 skipping to change at page 18, line 42
Received: from ... by ... Received: from ... by ...
From: =?UTF-8?Q?DISPLAY-LOCAL?= From: =?UTF-8?Q?DISPLAY-LOCAL?=
=?UTF-8?Q?NON-ASCII-LOCAL@example.com?= :; =?UTF-8?Q?NON-ASCII-LOCAL@example.com?= :;
To: =?UTF-8?Q?DISPLAY-REMOTE1?= To: =?UTF-8?Q?DISPLAY-REMOTE1?=
=?UTF-8?Q?NON-ASCII-REMOTE1@example.net?= :;, =?UTF-8?Q?NON-ASCII-REMOTE1@example.net?= :;,
=?UTF-8?Q?DISPLAY-REMOTE2?= =?UTF-8?Q?DISPLAY-REMOTE2?=
=?UTF-8?Q?NON-ASCII-REMOTE2@example.com?= :;, =?UTF-8?Q?NON-ASCII-REMOTE2@example.com?= :;,
Cc: =?UTF-8?Q?DISPLAY-REMOTE3?= Cc: =?UTF-8?Q?DISPLAY-REMOTE3?=
=?UTF-8?Q?NON-ASCII-REMOTE3@example.org?= :; =?UTF-8?Q?NON-ASCII-REMOTE3@example.org?= :;
Subject: =?UTF-8?Q?NON-ASCII-SUBJECT?= Subject: =?UTF-8?Q?NON-ASCII-SUBJECT?=
Date: DATE Date: Mon, 30 Jul 2012 01:23:45 -0000
Downgraded-Message-Id: =?UTF-8?Q?MESSAGE_ID?= Downgraded-Message-Id: =?UTF-8?Q?MESSAGE_ID?=
Mime-Version: 1.0 Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8" Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit Content-Transfer-Encoding: 8bit
X-Unknown-Header: =?UTF-8?Q?NON-ASCII-CHARACTERS?= X-Unknown-Header: =?UTF-8?Q?NON-ASCII-CHARACTERS?=
MAIL_BODY MAIL_BODY
Figure 2: Downgraded message Figure 2: Downgraded message
Appendix B. Change History
[[RFC Editor: Please remove this section prior to publication.]]
This section is used for tracking the update of this document. Will
be removed after finalize.
B.1. Version 00
o Initial version
o Imported header field downgrading from RFC 5504
B.2. Version 01
o same as Version 00
B.3. Version 02
o Added updating RFC 5322 to allow <group> syntax in From: and
Sender
o Added GROUP Downgrading
B.4. Version 03
o Replaced <utf8-addr-spec> with <addr-spec>
o Added updating RFC 5322 to allow <group> syntax in From: and
Sender
o Added one sentence in Security considerations
o Updated IANA considerations
B.5. Version 04
o Removed "Internationalized Address removed" from GROUP and MAILBOX
downgrading
o Updated "Updating RFC 5322"
o Compacted new header field definition
o Compacted security considerations
o Updated IANA considerations to remove obsoleting header fields
that are registered by RFC 5504
o Added a discussion of alternate downgrading models for the POP and
IMAP cases.
o Incorporated a large number of editorial changes to improve
clarity.
B.6. Version 05
o Some text corrections
o Terminology change: only to use non-ASCII address, non-ASCII
message, non-ASCII string and imported them from RFC 6530 and RFC
6532
o Replace "non-ASCII character" with "non-ASCII string"
o Removed 5.1.1. RECEIVED Downgrading
B.7. Version 06
o Removed "Updating RFC 5322"
o Added reference to draft-leiba-5322upd-from-group
B.8. Version 07
o Updated by WGLC comments
o Fixed Received downgrading and added to refer "RFC 6531", "RFC
5890", "RFC 5891"
o Added Domain downgrading for Received, Group and Mailbox
o Swapped section 3 and 4
Author's Address Author's Address
Kazunori Fujiwara Kazunori Fujiwara
Japan Registry Services Co., Ltd. Japan Registry Services Co., Ltd.
Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda
Chiyoda-ku, Tokyo 101-0065 Chiyoda-ku, Tokyo 101-0065
Japan Japan
Phone: +81 3 5215 8451 Phone: +81 3 5215 8451
EMail: fujiwara@wide.ad.jp, fujiwara@jprs.co.jp EMail: fujiwara@wide.ad.jp, fujiwara@jprs.co.jp
 End of changes. 66 change blocks. 
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