draft-ietf-eai-frmwrk-4952bis-02.txt   draft-ietf-eai-frmwrk-4952bis-03.txt 
Email Address Internationalization J. Klensin Email Address Internationalization J. Klensin
(EAI) (EAI)
Internet-Draft Y. Ko Internet-Draft Y. Ko
Obsoletes: RFCs 4952, 5504, 5825 ICU Obsoletes: RFCs 4952, 5504, 5825 ICU
(if approved) July 12, 2010 (if approved) August 16, 2010
Intended status: Informational Intended status: Informational
Expires: January 13, 2011 Expires: February 17, 2011
Overview and Framework for Internationalized Email Overview and Framework for Internationalized Email
draft-ietf-eai-frmwrk-4952bis-02 draft-ietf-eai-frmwrk-4952bis-03
Abstract Abstract
Full use of electronic mail throughout the world requires that, Full use of electronic mail throughout the world requires that,
subject to other constraints, people be able to use close variations subject to other constraints, people be able to use close variations
on their own names, written correctly in their own languages and on their own names, written correctly in their own languages and
scripts, as mailbox names in email addresses. This document scripts, as mailbox names in email addresses. This document
introduces a series of specifications that define mechanisms and introduces a series of specifications that define mechanisms and
protocol extensions needed to fully support internationalized email protocol extensions needed to fully support internationalized email
addresses. These changes include an SMTP extension and extension of addresses. These changes include an SMTP extension and extension of
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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 13, 2011. This Internet-Draft will expire on February 17, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 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
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Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Role of This Specification . . . . . . . . . . . . . . . . . . 5 2. Role of This Specification . . . . . . . . . . . . . . . . . . 4
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 5 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 5
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Mail User and Mail Transfer Agents . . . . . . . . . . . . 6 4.1. Mail User and Mail Transfer Agents . . . . . . . . . . . . 6
4.2. Address Character Sets . . . . . . . . . . . . . . . . . . 7 4.2. Address Character Sets . . . . . . . . . . . . . . . . . . 6
4.3. User Types . . . . . . . . . . . . . . . . . . . . . . . . 7 4.3. User Types . . . . . . . . . . . . . . . . . . . . . . . . 7
4.4. Messages . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.4. Messages . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.5. Mailing Lists . . . . . . . . . . . . . . . . . . . . . . 8 4.5. Mailing Lists . . . . . . . . . . . . . . . . . . . . . . 8
4.6. Conventional Message and Internationalized Message . . . . 8 4.6. Conventional Message and Internationalized Message . . . . 8
4.7. Undeliverable Messages and Notification . . . . . . . . . 8 4.7. Undeliverable Messages and Notification . . . . . . . . . 8
5. Overview of the Approach and Document Plan . . . . . . . . . . 9 5. Overview of the Approach and Document Plan . . . . . . . . . . 8
6. Overview of Protocol Extensions and Changes . . . . . . . . . 9 6. Review of Experimental Results . . . . . . . . . . . . . . . . 9
6.1. SMTP Extension for Internationalized Email Address . . . . 9 7. Overview of Protocol Extensions and Changes . . . . . . . . . 10
6.2. Transmission of Email Header Fields in UTF-8 Encoding . . 10 7.1. SMTP Extension for Internationalized Email Address . . . . 10
6.3. SMTP Service Extension for DSNs . . . . . . . . . . . . . 11 7.2. Transmission of Email Header Fields in UTF-8 Encoding . . 11
7. Downgrading before and after SMTP Transactions . . . . . . . . 11 7.3. SMTP Service Extension for DSNs . . . . . . . . . . . . . 12
7.1. Downgrading before or during Message Submission . . . . . 12 8. Downgrading before and after SMTP Transactions . . . . . . . . 12
7.2. Downgrading or Other Processing After Final SMTP 8.1. Downgrading before or during Message Submission . . . . . 13
Delivery . . . . . . . . . . . . . . . . . . . . . . . . . 13 8.2. Downgrading or Other Processing After Final SMTP
8. Downgrading in Transit . . . . . . . . . . . . . . . . . . . . 13 Delivery . . . . . . . . . . . . . . . . . . . . . . . . . 14
9. User Interface and Configuration Issues . . . . . . . . . . . 14 9. Downgrading in Transit . . . . . . . . . . . . . . . . . . . . 14
9.1. Choices of Mailbox Names and Unicode Normalization . . . . 14 10. User Interface and Configuration Issues . . . . . . . . . . . 15
10. Additional Issues . . . . . . . . . . . . . . . . . . . . . . 15 10.1. Choices of Mailbox Names and Unicode Normalization . . . . 15
10.1. Impact on URIs and IRIs . . . . . . . . . . . . . . . . . 16 11. Additional Issues . . . . . . . . . . . . . . . . . . . . . . 16
10.2. Use of Email Addresses as Identifiers . . . . . . . . . . 16 11.1. Impact on URIs and IRIs . . . . . . . . . . . . . . . . . 16
10.3. Encoded Words, Signed Messages, and Downgrading . . . . . 16 11.2. Use of Email Addresses as Identifiers . . . . . . . . . . 16
10.4. LMTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 11.3. Encoded Words, Signed Messages, and Downgrading . . . . . 17
10.5. Other Uses of Local Parts . . . . . . . . . . . . . . . . 17 11.4. LMTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
10.6. Non-Standard Encapsulation Formats . . . . . . . . . . . . 17 11.5. Other Uses of Local Parts . . . . . . . . . . . . . . . . 17
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 11.6. Non-Standard Encapsulation Formats . . . . . . . . . . . . 18
12. Security Considerations . . . . . . . . . . . . . . . . . . . 17 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19 13. Security Considerations . . . . . . . . . . . . . . . . . . . 18
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
14.1. Normative References . . . . . . . . . . . . . . . . . . . 19 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
14.2. Informative References . . . . . . . . . . . . . . . . . . 21 15.1. Normative References . . . . . . . . . . . . . . . . . . . 20
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 24 15.2. Informative References . . . . . . . . . . . . . . . . . . 22
A.1. Changes between -00 and -01 . . . . . . . . . . . . . . . 24 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 25
A.2. Changes between -01 and -02 . . . . . . . . . . . . . . . 24 A.1. Changes between -00 and -01 . . . . . . . . . . . . . . . 25
A.2. Changes between -01 and -02 . . . . . . . . . . . . . . . 26
A.3. Changes between -02 and -03 . . . . . . . . . . . . . . . 27
1. Introduction 1. Introduction
[[anchor1: Note to EAI WG: All comments received on the mailing list Note in Draft and to RFC Editor: The keyword represented in this
about this document have been incorporated into the -02 draft. As document by "UTF8SMTPbis" (and in the XML source by &EAISMTPkeyword;)
indicated in earlier notes, most placeholders have been removed from is a placeholder. The actual keyword will be assigned when the
it to make the document a WG Last Call candidate. A note was posted standards track SMTP extension in this series [RFC5336bis-SMTP] is
on 9 July listing outstanding topics needing discussion in -01 approved for publication and should be substituted here. This
(http://www.ietf.org/mail-archive/web/ima/current/msg03259.html) to paragraph should be treated as normative reference to that SMTP
which there was no response before -02 was submitted. It may be extension draft, creating a reference hold until it is approved by
useful to refer to that note and the change log below as part of the IESG. The paragraph should be removed before RFC publication.
review of this draft.]]
In order to use internationalized email addresses, we need to In order to use internationalized email addresses, we need to
internationalize both the domain part and the local part of email internationalize both the domain part and the local part of email
addresses. The domain part of email addresses is already addresses. The domain part of email addresses is already
internationalized [RFC5890], while the local part is not. internationalized [RFC5890], while the local part is not. Without
[[anchor2: Note in Draft: RFC 5890, formerly draft-ietf-idnabis-defs, the extensions specified in this document, the mailbox name is
and the closely-related RFC 5891 - 5894, have been in AUTH48 since restricted to a subset of 7-bit ASCII [RFC5321]. Though MIME
June 6. None of the the author, WG leadership, or ADs are holding it
up. Using the I-D references here is just extra work.]]
Without the extensions specified in this document, the mailbox name
is restricted to a subset of 7-bit ASCII [RFC5321]. Though MIME
[RFC2045] enables the transport of non-ASCII data, it does not [RFC2045] enables the transport of non-ASCII data, it does not
provide a mechanism for internationalized email addresses. In RFC provide a mechanism for internationalized email addresses. In RFC
2047 [RFC2047], MIME defines an encoding mechanism for some specific 2047 [RFC2047], MIME defines an encoding mechanism for some specific
message header fields to accommodate non-ASCII data. However, it message header fields to accommodate non-ASCII data. However, it
does not permit the use of email addresses that include non-ASCII does not permit the use of email addresses that include non-ASCII
characters. Without the extensions defined here, or some equivalent characters. Without the extensions defined here, or some equivalent
set, the only way to incorporate non-ASCII characters in any part of set, the only way to incorporate non-ASCII characters in any part of
email addresses is to use RFC 2047 coding to embed them in what RFC email addresses is to use RFC 2047 coding to embed them in what RFC
5322 [RFC5322] calls the "display name" (known as a "name phrase" or 5322 [RFC5322] calls the "display name" (known as a "name phrase" or
by other terms elsewhere) of the relevant header fields. Information by other terms elsewhere) of the relevant header fields. Information
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This document presents the overview and framework for an approach to This document presents the overview and framework for an approach to
the next stage of email internationalization. This new stage the next stage of email internationalization. This new stage
requires not only internationalization of addresses and header requires not only internationalization of addresses and header
fields, but also associated transport and delivery models. A prior fields, but also associated transport and delivery models. A prior
version of this specification, RFC 4952 [RFC4952], also provided an version of this specification, RFC 4952 [RFC4952], also provided an
introduction to a series of experimental protocols [RFC5335] introduction to a series of experimental protocols [RFC5335]
[RFC5336] [RFC5337] [RFC5504] [RFC5721] [RFC5738] [RFC5825]. This [RFC5336] [RFC5337] [RFC5504] [RFC5721] [RFC5738] [RFC5825]. This
revised form provides overview and conceptual information for the revised form provides overview and conceptual information for the
standards-track successors of a subset of those protocols. Details standards-track successors of a subset of those protocols. Details
of the documents and the relationships among them appear in of the documents and the relationships among them appear in Section 5
Section 5. and a discussion of what was learned from the Experimental protocols
and their implementations appears in Section 6.
Taken together, these specifications provide the details for a way to Taken together, these specifications provide the details for a way to
implement and support internationalized email. The document itself implement and support internationalized email. The document itself
describes how the various elements of email internationalization fit describes how the various elements of email internationalization fit
together and the relationships among the primary specifications together and the relationships among the primary specifications
associated with message transport, header formats, and handling. associated with message transport, header formats, and handling.
3. Problem Statement 3. Problem Statement
Internationalizing Domain Names in Applications (IDNA) [RFC5890] Internationalizing Domain Names in Applications (IDNA) [RFC5890]
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repertoire [ASCII]; an address is "non-ASCII", or an "i18n-address", repertoire [ASCII]; an address is "non-ASCII", or an "i18n-address",
if any character is not in the ASCII character repertoire. Such if any character is not in the ASCII character repertoire. Such
addresses may be restricted in other ways, but those restrictions are addresses may be restricted in other ways, but those restrictions are
not relevant to this definition. The term "all-ASCII" is also not relevant to this definition. The term "all-ASCII" is also
applied to other protocol elements when the distinction is important, applied to other protocol elements when the distinction is important,
with "non-ASCII" or "internationalized" as its opposite. with "non-ASCII" or "internationalized" as its opposite.
The umbrella term to describe the email address internationalization The umbrella term to describe the email address internationalization
specified by this document and its companion documents is specified by this document and its companion documents is
"UTF8SMTPbis". "UTF8SMTPbis".
[[anchor5: Note in Draft: Keyword to be changed before publication.]] [[anchor3: Note in Draft: Keyword to be changed before publication.]]
For example, an address permitted by this specification is referred For example, an address permitted by this specification is referred
to as a "UTF8SMTPbis (compliant) address". to as a "UTF8SMTPbis (compliant) address".
Please note that, according to the definitions given here, the set of Please note that, according to the definitions given here, the set of
all "all-ASCII" addresses and the set of all "non-ASCII" addresses all "all-ASCII" addresses and the set of all "non-ASCII" addresses
are mutually exclusive. The set of all addresses permitted when are mutually exclusive. The set of all addresses permitted when
UTF8SMTPbis appears is the union of these two sets. UTF8SMTPbis appears is the union of these two sets.
4.3. User Types 4.3. User Types
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o Extensions to delivery status and notification handling to adapt o Extensions to delivery status and notification handling to adapt
to internationalized addresses [RFC5337bis-DSN]. to internationalized addresses [RFC5337bis-DSN].
o Extensions to the IMAP protocol to support internationalized o Extensions to the IMAP protocol to support internationalized
message headers [RFC5738bis-IMAP]. message headers [RFC5738bis-IMAP].
o Parallel extensions to the POP protocol [RFC5721] o Parallel extensions to the POP protocol [RFC5721]
[RFC5721bis-POP3]. [RFC5721bis-POP3].
6. Overview of Protocol Extensions and Changes 6. Review of Experimental Results
6.1. SMTP Extension for Internationalized Email Address The key difference between this set of protocols and the experimental
set that preceded them [RFC5335] [RFC5336] [RFC5337] [RFC5504]
[RFC5721] [RFC5738] [RFC5825] is that the earlier group provided a
mechanism for in-transit downgrading of messages (described in detail
in RFC 5504). That mechanism permitted, and essentially required,
that each non-ASCII address be accompanied by an all-ASCII
equivalent. That, in turn, raised security concerns associated with
pairing of addresses that could not be authenticated. It also
introduced the first incompatible change to Internet mail addressing
in many years, raising concerns about interoperability issues if the
new address forms "leaked" into legacy email implementations. The WG
concluded that the advantages of in-transit downgrading, were it
feasible operationally, would be significant enough to overcome those
concerns.
Operationally that turned out to not be the case, with
interoperability problems among initial implementations. Prior to
starting on the work that led to this set of specifications, the WG
concluded that the combination of requirements and long-term
implications of that earlier model were too complex to be
satisfactory and that work should move ahead without it.
7. Overview of Protocol Extensions and Changes
7.1. SMTP Extension for Internationalized Email Address
An SMTP extension, "UTF8SMTPbis" is specified as follows: An SMTP extension, "UTF8SMTPbis" is specified as follows:
o Permits the use of UTF-8 strings in email addresses, both local o Permits the use of UTF-8 strings in email addresses, both local
parts and domain names. parts and domain names.
o Permits the selective use of UTF-8 strings in email message o Permits the selective use of UTF-8 strings in email message
headers (see Section 6.2). headers (see Section 7.2).
o Requires that the server advertise the 8BITMIME extension o Requires that the server advertise the 8BITMIME extension
[RFC1652] and that the client support 8-bit transmission so that [RFC1652] and that the client support 8-bit transmission so that
header information can be transmitted without using a special header information can be transmitted without using a special
content-transfer-encoding. content-transfer-encoding.
Some general principles affect the development decisions underlying Some general principles affect the development decisions underlying
this work. this work.
1. Email addresses enter subsystems (such as a user interface) that 1. Email addresses enter subsystems (such as a user interface) that
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transmitted over the Internet. There is no practical way to transmitted over the Internet. There is no practical way to
identify multiple charsets properly with an extension similar to identify multiple charsets properly with an extension similar to
this without introducing great complexity. this without introducing great complexity.
Conformance to the group of standards specified here for email Conformance to the group of standards specified here for email
transport and delivery requires implementation of the SMTP Extension transport and delivery requires implementation of the SMTP Extension
specification and the UTF-8 Header specification. If the system specification and the UTF-8 Header specification. If the system
implements IMAP or POP, it MUST conform to the i18n IMAP or POP implements IMAP or POP, it MUST conform to the i18n IMAP or POP
specifications respectively. specifications respectively.
6.2. Transmission of Email Header Fields in UTF-8 Encoding 7.2. Transmission of Email Header Fields in UTF-8 Encoding
There are many places in MUAs or in a user presentation in which There are many places in MUAs or in a user presentation in which
email addresses or domain names appear. Examples include the email addresses or domain names appear. Examples include the
conventional From, To, or Cc header fields; Message-ID and conventional From, To, or Cc header fields; Message-ID and
In-Reply-To header fields that normally contain domain names (but In-Reply-To header fields that normally contain domain names (but
that may be a special case); and in message bodies. Each of these that may be a special case); and in message bodies. Each of these
must be examined from an internationalization perspective. The user must be examined from an internationalization perspective. The user
will expect to see mailbox and domain names in local characters, and will expect to see mailbox and domain names in local characters, and
to see them consistently. If non-obvious encodings, such as to see them consistently. If non-obvious encodings, such as
protocol-specific ASCII-Compatible Encoding (ACE) variants, are used, protocol-specific ASCII-Compatible Encoding (ACE) variants, are used,
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be in the fully internationalized form. That form should presumably be in the fully internationalized form. That form should presumably
use UTF-8 rather than ASCII as the base character set for the use UTF-8 rather than ASCII as the base character set for the
contents of header fields (protocol elements such as the header field contents of header fields (protocol elements such as the header field
names themselves are unchanged and remain entirely in ASCII). For names themselves are unchanged and remain entirely in ASCII). For
transition purposes and compatibility with legacy systems, this can transition purposes and compatibility with legacy systems, this can
done by extending the traditional MIME encoding models for non-ASCII done by extending the traditional MIME encoding models for non-ASCII
characters in headers [RFC2045] [RFC2231]. However, the target is characters in headers [RFC2045] [RFC2231]. However, the target is
fully internationalized message headers, as discussed in fully internationalized message headers, as discussed in
[RFC5335bis-Hdrs] and not an extended and painful transition. [RFC5335bis-Hdrs] and not an extended and painful transition.
6.3. SMTP Service Extension for DSNs 7.3. SMTP Service Extension for DSNs
The existing Draft Standard Delivery status notifications (DSNs) The existing Draft Standard Delivery status notifications (DSNs)
specification [RFC3461] is limited to ASCII text in the machine specification [RFC3461] is limited to ASCII text in the machine
readable portions of the protocol. "International Delivery and readable portions of the protocol. "International Delivery and
Disposition Notifications" [RFC5337bis-DSN] adds a new address type Disposition Notifications" [RFC5337bis-DSN] adds a new address type
for international email addresses so an original recipient address for international email addresses so an original recipient address
with non-ASCII characters can be correctly preserved even after with non-ASCII characters can be correctly preserved even after
downgrading. If an SMTP server advertises both the UTF8SMTPbis and downgrading. If an SMTP server advertises both the UTF8SMTPbis and
the DSN extension, that server MUST implement internationalized DSNs the DSN extension, that server MUST implement internationalized DSNs
including support for the ORCPT parameter specified in RFC 3461 including support for the ORCPT parameter specified in RFC 3461
[RFC3461]. [RFC3461].
7. Downgrading before and after SMTP Transactions 8. Downgrading before and after SMTP Transactions
An important issue with these extensions is how to handle An important issue with these extensions is how to handle
interactions between systems that support non-ASCII addresses and interactions between systems that support non-ASCII addresses and
legacy systems that expect ASCII. There is, of course, no problem legacy systems that expect ASCII. There is, of course, no problem
with ASCII-only systems sending to those that can handle with ASCII-only systems sending to those that can handle
internationalized forms because the ASCII forms are just a proper internationalized forms because the ASCII forms are just a proper
subset. But, when systems that support these extensions send mail, subset. But, when systems that support these extensions send mail,
they may include non-ASCII addresses for senders, receivers, or both they may include non-ASCII addresses for senders, receivers, or both
and might also provide non-ASCII header information other than and might also provide non-ASCII header information other than
addresses. If the extension is not supported by the first-hop system addresses. If the extension is not supported by the first-hop system
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imply that the originating user or system must have ASCII-only imply that the originating user or system must have ASCII-only
addresses available for all senders and recipients. Mechanisms by addresses available for all senders and recipients. Mechanisms by
which such addresses may be found or identified are outside the scope which such addresses may be found or identified are outside the scope
of these specifications as are decisions about the design of of these specifications as are decisions about the design of
originating systems such as whether any required transformations are originating systems such as whether any required transformations are
made by the user, the originating MUA, or the Submission server. made by the user, the originating MUA, or the Submission server.
A somewhat more complex situation arises when the first-hop system A somewhat more complex situation arises when the first-hop system
supports these extensions but some subsequent server in the SMTP supports these extensions but some subsequent server in the SMTP
transmission chain does not. It is important to note that most cases transmission chain does not. It is important to note that most cases
of that situation will be the result of configuration errors: of that situation with forward-pointing addresses will be the result
especially if it hosts non-ASCII addresses, a final delivery MTA that of configuration errors: especially if it hosts non-ASCII addresses,
accepts these extensions should not be configured with lower- a final delivery MTA that accepts these extensions should not be
preference MX hosts that do not. While the experiments that preceded configured with lower-preference MX hosts that do not. When the only
these specifications included a mechanism for passing backup ASCII non-ASCII address being transmitted is backward-pointing (e.g., in an
addresses to intermediate relay systems and having those systems SMTP MAIL command), recipient configuration can not help in general.
alter the relevant message header fields and substitute the addresses On the other hand, alternate, all-ASCII, addresses for senders are
[RFC5504], the requirements and long-term implications of that system those most likely to be authoritatively known by the submission
proved too complex to be satisfactory. Consequently, if an environment or the sender herself. Consequently, if an intermediate
intermediate SMTP relay that is transmitting a message that requires SMTP relay that is transmitting a message that requires these
these extensions and discovers that the next system in the chain does extensions and discovers that the next system in the chain does not
not support them, it will have little choice other than to reject or support them, it will have little choice other than to reject or
return the message. return the message.
As discussed above, downgrading to an ASCII-only form may occur As discussed above, downgrading to an ASCII-only form may occur
before or during the initial message submission. It might also occur before or during the initial message submission. It might also occur
after the delivery to the final delivery MTA in order to accommodate after the delivery to the final delivery MTA in order to accommodate
messages stores or IMAP or POP servers or clients that have different messages stores or IMAP or POP servers or clients that have different
capabilities than the delivery MTA. These two cases are discussed in capabilities than the delivery MTA. These two cases are discussed in
the subsections below. the subsections below.
7.1. Downgrading before or during Message Submission 8.1. Downgrading before or during Message Submission
It is likely that the most common cases in which a message that
requires these extensions is sent to a system that does not will
involve the combination of ASCII-only forward-pointing addresses with
a non-ASCII backward-pointing one. Until the extensions described
here have been universally implemented in the Internet email
environment, senders who prefer to use non-ASCII addresses (or raw
UTF-8 characters in header fields) even when their intended
recipients use and expect all-ASCII ones will need to be especially
careful about the error conditions that can arise, especially if they
are working in an environment in which non-delivery messages (or
other indications from submission servers) are routinely dropped or
ignored.
Perhaps obviously, the most convenient time to find an ASCII address Perhaps obviously, the most convenient time to find an ASCII address
corresponding to an internationalized address is at the originating corresponding to an internationalized address is at the originating
MUA. This can occur either before the message is sent or after the MUA or closely-associated systems. This can occur either before the
internationalized form of the message is rejected. It is also the message is sent or after the internationalized form of the message is
most convenient time to convert a message from the internationalized rejected. It is also the most convenient time to convert a message
form into conventional ASCII form or to generate a non-delivery from the internationalized form into conventional ASCII form or to
message to the sender if either is necessary. At that point, the generate a non-delivery message to the sender if either is necessary.
user has a full range of choices available, including contacting the At that point, the user has a full range of choices available,
including changing backward-pointing addresses, contacting the
intended recipient out of band for an alternate address, consulting intended recipient out of band for an alternate address, consulting
appropriate directories, arranging for translation of both addresses appropriate directories, arranging for translation of both addresses
and message content into a different language, and so on. While it and message content into a different language, and so on. While it
is natural to think of message downgrading as optimally being a is natural to think of message downgrading as optimally being a
fully-automated process, we should not underestimate the capabilities fully-automated process, we should not underestimate the capabilities
of a user of at least moderate intelligence who wishes to communicate of a user of at least moderate intelligence who wishes to communicate
with another such user. with another such user.
In this context, one can easily imagine modifications to message In this context, one can easily imagine modifications to message
submission servers (as described in [RFC4409]) so that they would submission servers (as described in [RFC4409]) so that they would
perform downgrading, or perhaps even upgrading, operations, receiving perform downgrading, or perhaps even upgrading, operations, receiving
messages with one or more of the internationalization extensions messages with one or more of the internationalization extensions
discussed here and adapting the outgoing message, as needed, to discussed here and adapting the outgoing message, as needed, to
respond to the delivery or next-hop environment it encounters. respond to the delivery or next-hop environment it encounters.
7.2. Downgrading or Other Processing After Final SMTP Delivery 8.2. Downgrading or Other Processing After Final SMTP Delivery
When an email message is received by a final delivery MTA, it is When an email message is received by a final delivery MTA, it is
usually stored in some form. Then it is retrieved either by software usually stored in some form. Then it is retrieved either by software
that reads the stored form directly or by client software via some that reads the stored form directly or by client software via some
email retrieval mechanisms such as POP or IMAP. email retrieval mechanisms such as POP or IMAP.
The SMTP extension described in Section 6.1 provides protection only The SMTP extension described in Section 7.1 provides protection only
in transport. It does not prevent MUAs and email retrieval in transport. It does not prevent MUAs and email retrieval
mechanisms that have not been upgraded to understand mechanisms that have not been upgraded to understand
internationalized addresses and UTF-8 message headers from accessing internationalized addresses and UTF-8 message headers from accessing
stored internationalized emails. stored internationalized emails.
Since the final delivery MTA (or, to be more specific, its Since the final delivery MTA (or, to be more specific, its
corresponding mail storage agent) cannot safely assume that agents corresponding mail storage agent) cannot safely assume that agents
accessing email storage will always be capable of handling the accessing email storage will always be capable of handling the
extensions proposed here, it MAY either downgrade internationalized extensions proposed here, it MAY either downgrade internationalized
emails or specially identify messages that utilize these extensions, emails or specially identify messages that utilize these extensions,
or both. If this is done, the final delivery MTA SHOULD include a or both. If this is done, the final delivery MTA SHOULD include a
mechanism to preserve or recover the original internationalized forms mechanism to preserve or recover the original internationalized forms
without information loss to support access by UTF8SMTPbis-aware without information loss to support access by UTF8SMTPbis-aware
agents. agents.
8. Downgrading in Transit 9. Downgrading in Transit
The base SMTP specification (Section 2.3.11 of RFC 5321 [RFC5321]) The base SMTP specification (Section 2.3.11 of RFC 5321 [RFC5321])
states that "due to a long history of problems when intermediate states that "due to a long history of problems when intermediate
hosts have attempted to optimize transport by modifying them, the hosts have attempted to optimize transport by modifying them, the
local-part MUST be interpreted and assigned semantics only by the local-part MUST be interpreted and assigned semantics only by the
host specified in the domain part of the address". This is not a new host specified in the domain part of the address". This is not a new
requirement; equivalent statements appeared in specifications in 2001 requirement; equivalent statements appeared in specifications in 2001
[RFC2821] and even in 1989 [RFC1123]. [RFC2821] and even in 1989 [RFC1123].
Adherence to this rule means that a downgrade mechanism that Adherence to this rule means that a downgrade mechanism that
transforms the local-part of an email address cannot be done in transforms the local-part of an email address cannot be utilized in
transit. It can only be done at the endpoints, namely by the MUA or transit. It can only be applied at the endpoints, specifically by
submission server or by the final delivery MTA. the MUA or submission server or by the final delivery MTA.
One of the reasons for this rule has to do with legacy email systems One of the reasons for this rule has to do with legacy email systems
that use source routing in the local-part of the address field. that embed mail routing information in the local-part of the address
Transforming the email address destroys such routing information. field. Transforming the email address destroys such routing
There is no way a server other than the final delivery server can information. There is no way a server other than the final delivery
know, for example, whether the local-part of user&foo@example.com is server can know, for example, whether the local-part of
a route ("user" is reached via "foo") or simply a local address. user%foo@example.com is a route ("user" is reached via "foo") or
simply a local address.
9. User Interface and Configuration Issues 10. User Interface and Configuration Issues
Internationalization of addresses and message headers, especially in Internationalization of addresses and message headers, especially in
combination with variations on character coding that are inherent to combination with variations on character coding that are inherent to
Unicode, may make careful choices of addresses and careful Unicode, may make careful choices of addresses and careful
configuration of servers and DNS records even more important than configuration of servers and DNS records even more important than
they are for traditional Internet email. It is likely that, as they are for traditional Internet email. It is likely that, as
experience develops with the use of these protocols, it will be experience develops with the use of these protocols, it will be
desirable to produce one or more additional documents that offer desirable to produce one or more additional documents that offer
guidance for configuration and interfaces. A document that discusses guidance for configuration and interfaces. A document that discusses
issues with mail user agents (MUAs), especially with regard to issues with mail user agents (MUAs), especially with regard to
downgrading, is expected to be developed in the EAI Working Group. downgrading [EAI-MUA-issues], is expected to be developed in the EAI
[[anchor15: Note in Draft: What do we want to do about this?]] Working Group. The subsections below address some other issues.
The subsections below address some other issues.
9.1. Choices of Mailbox Names and Unicode Normalization 10.1. Choices of Mailbox Names and Unicode Normalization
It has long been the case that the email syntax permits choices about It has long been the case that the email syntax permits choices about
mailbox names that are unwise in practice if one actually intends the mailbox names that are unwise in practice if one actually intends the
mailboxes to be accessible to a broad range of senders. The most- mailboxes to be accessible to a broad range of senders. The most-
often-cited examples involve the use of case-sensitivity and tricky often-cited examples involve the use of case-sensitivity and tricky
quoting of embedded characters in mailbox local parts. While these quoting of embedded characters in mailbox local parts. While these
are permitted by the protocols and servers are expected to support are permitted by the protocols and servers are expected to support
them and there are special cases where they can provide value, taking them and there are special cases where they can provide value, taking
advantage of those features is almost always bad practice unless the advantage of those features is almost always bad practice unless the
intent is to create some form of security by obscurity. intent is to create some form of security by obscurity.
In the absence of these extensions, SMTP clients and servers are In the absence of these extensions, SMTP clients and servers are
constrained to using only those addresses permitted by RFC 5321. The constrained to using only those addresses permitted by RFC 5321. The
local parts of those addresses MAY be made up of any ASCII characters local parts of those addresses MAY be made up of any ASCII characters
except the control characters that 5321 prohibits, although some of except the control characters that 5321 prohibits, although some of
them MUST be quoted as specified there. It is notable in an them MUST be quoted as specified there. It is notable in an
internationalization context that there is a long history on some internationalization context that there is a long history on some
systems of using overstruck ASCII characters (a character, a systems of using overstruck ASCII characters (a character, a
backspace, and another character) within a quoted string to backspace, and another character) within a quoted string to
approximate non-ASCII characters. This form of internationalization approximate non-ASCII characters. This form of internationalization
was permitted by RFC 821 but is prohibited by RFC 5321 because it was permitted by RFC 821 [RFC0821] but is prohibited by RFC 5321
requires a backspace character (a prohibited C0 control). The because it requires a backspace character (a prohibited C0 control).
practice SHOULD be phased out as this extension becomes widely The practice SHOULD be phased out as this extension becomes widely
deployed but backward-compatibility considerations may require that deployed but backward-compatibility considerations may require that
it continue to be recognized. it continue to be recognized.
For the particular case of EAI mailbox names, special attention must For the particular case of EAI mailbox names, special attention must
be paid to Unicode normalization [Unicode-UAX15], in part because be paid to Unicode normalization [Unicode-UAX15], in part because
Unicode strings may be normalized by other processes independent of Unicode strings may be normalized by other processes independent of
what a mail protocol specifies (this is exactly analogous to what may what a mail protocol specifies (this is exactly analogous to what may
happen with quoting and dequoting in traditional addresses). happen with quoting and dequoting in traditional addresses).
Consequently, the following principles are offered as advice to those Consequently, the following principles are offered as advice to those
who are selecting names for mailboxes: who are selecting names for mailboxes:
o In general, it is wise to support addresses in Normalized form, o In general, it is wise to support addresses in Normalized form,
using either Normalization Form NFC and, except in unusual using either Normalization Form NFC and, except in unusual
circumstances, NFKC. circumstances, NFKC.
o It may be wise to support other forms of the same local-part o It may be wise to support other forms of the same local-part
string, either as aliases or by normalization of strings reaching string, either as aliases or by normalization of strings reaching
the delivery server, in the event that the sender does not send the delivery server, in the event that the sender does not send
skipping to change at page 15, line 43 skipping to change at page 16, line 33
* C0 (and presumably C1) controls (see The Unicode Standard * C0 (and presumably C1) controls (see The Unicode Standard
[Unicode52]) are prohibited, the first in RFC 5321 and the [Unicode52]) are prohibited, the first in RFC 5321 and the
second by an obvious extension from it [RFC5198]. second by an obvious extension from it [RFC5198].
* Other kinds of punctuation, spaces, etc., are risky practice. * Other kinds of punctuation, spaces, etc., are risky practice.
Perhaps they will work, and SMTP receiver code is required to Perhaps they will work, and SMTP receiver code is required to
handle them, but creating dependencies on them in mailbox names handle them, but creating dependencies on them in mailbox names
that are chosen is usually a bad practice and may lead to that are chosen is usually a bad practice and may lead to
interoperability problems. interoperability problems.
10. Additional Issues 11. Additional Issues
This section identifies issues that are not covered, or not covered This section identifies issues that are not covered, or not covered
comprehensively, as part of this set of specifications, but that will comprehensively, as part of this set of specifications, but that will
require ongoing review as part of deployment of email address and require ongoing review as part of deployment of email address and
header internationalization. header internationalization.
10.1. Impact on URIs and IRIs 11.1. Impact on URIs and IRIs
The mailto: schema [RFC2368] and discussed in the Internationalized The mailto: schema [RFC2368] and discussed in the Internationalized
Resource Identifier (IRI) specification [RFC3987] may need to be Resource Identifier (IRI) specification [RFC3987] may need to be
modified when this work is completed and standardized. modified when this work is completed and standardized.
10.2. Use of Email Addresses as Identifiers 11.2. Use of Email Addresses as Identifiers
There are a number of places in contemporary Internet usage in which There are a number of places in contemporary Internet usage in which
email addresses are used as identifiers for individuals, including as email addresses are used as identifiers for individuals, including as
identifiers to Web servers supporting some electronic commerce sites identifiers to Web servers supporting some electronic commerce sites
and in some X.509 certificates [RFC5280]. These documents do not and in some X.509 certificates [RFC5280]. These documents do not
address those uses, but it is reasonable to expect that some address those uses, but it is reasonable to expect that some
difficulties will be encountered when internationalized addresses are difficulties will be encountered when internationalized addresses are
first used in those contexts, many of which cannot even handle the first used in those contexts, many of which cannot even handle the
full range of addresses permitted today. full range of addresses permitted today.
10.3. Encoded Words, Signed Messages, and Downgrading 11.3. Encoded Words, Signed Messages, and Downgrading
One particular characteristic of the email format is its persistency: One particular characteristic of the email format is its persistency:
MUAs are expected to handle messages that were originally sent MUAs are expected to handle messages that were originally sent
decades ago and not just those delivered seconds ago. As such, MUAs decades ago and not just those delivered seconds ago. As such, MUAs
and mail filtering software, such as that specified in Sieve and mail filtering software, such as that specified in Sieve
[RFC5228], will need to continue to accept and decode header fields [RFC5228], will need to continue to accept and decode header fields
that use the "encoded word" mechanism [RFC2047] to accommodate non- that use the "encoded word" mechanism [RFC2047] to accommodate non-
ASCII characters in some header fields. While extensions to both ASCII characters in some header fields. While extensions to both
POP3 [RFC1939] and IMAP [RFC3501] have been defined that include POP3 [RFC1939] and IMAP [RFC3501] have been defined that include
automatic upgrading of messages that carry non-ASCII information in automatic upgrading of messages that carry non-ASCII information in
skipping to change at page 16, line 47 skipping to change at page 17, line 33
For example, message parts that are cryptographically signed, using For example, message parts that are cryptographically signed, using
e.g., S/MIME [RFC3851] or Pretty Good Privacy (PGP) [RFC3156], cannot e.g., S/MIME [RFC3851] or Pretty Good Privacy (PGP) [RFC3156], cannot
be upgraded from the RFC 2047 form to normal UTF-8 characters without be upgraded from the RFC 2047 form to normal UTF-8 characters without
breaking the signature. Similarly, message parts that are encrypted breaking the signature. Similarly, message parts that are encrypted
may contain, when decrypted, header fields that use the RFC 2047 may contain, when decrypted, header fields that use the RFC 2047
encoding; such messages cannot be 'fully' upgraded without access to encoding; such messages cannot be 'fully' upgraded without access to
cryptographic keys. cryptographic keys.
Similar issues may arise if messages are signed and then subsequently Similar issues may arise if messages are signed and then subsequently
downgraded, e.g., as discussed in Section 7.1, and then an attempt is downgraded, e.g., as discussed in Section 8.1, and then an attempt is
made to upgrade them to the original form and then verify the made to upgrade them to the original form and then verify the
signatures. Even the very subtle changes that may result from signatures. Even the very subtle changes that may result from
algorithms to downgrade and then upgrade again may be sufficient to algorithms to downgrade and then upgrade again may be sufficient to
invalidate the signatures if they impact either the primary or MIME invalidate the signatures if they impact either the primary or MIME
bodypart headers. When signatures are present, downgrading must be bodypart headers. When signatures are present, downgrading must be
performed with extreme care if at all. performed with extreme care if at all.
10.4. LMTP 11.4. LMTP
LMTP [RFC2033] may be used as part of the final delivery agent. In LMTP [RFC2033] may be used as part of the final delivery agent. In
such cases, LMTP may be arranged to deliver the mail to the mail such cases, LMTP may be arranged to deliver the mail to the mail
store. The mail store may not have UTF8SMTPbis capability. LMTP may store. The mail store may not have UTF8SMTPbis capability. LMTP may
need to be updated to deal with these situations. need to be updated to deal with these situations.
10.5. Other Uses of Local Parts 11.5. Other Uses of Local Parts
Local parts are sometimes used to construct domain labels, e.g., the Local parts are sometimes used to construct domain labels, e.g., the
local part "user" in the address user@domain.example could be local part "user" in the address user@domain.example could be
converted into a vanity host user.domain.example with its Web space converted into a vanity host user.domain.example with its Web space
at <http://user.domain.example> and the catchall addresses at <http://user.domain.example> and the catchall addresses
any.thing.goes@user.domain.example. any.thing.goes@user.domain.example.
Such schemes are obviously limited by, among other things, the SMTP Such schemes are obviously limited by, among other things, the SMTP
rules for domain names, and will not work without further rules for domain names, and will not work without further
restrictions for other local parts such as the <utf8-local-part> restrictions for other local parts such as the <utf8-local-part>
specified in [RFC5335bis-Hdrs]. Whether those limitations are specified in [RFC5335bis-Hdrs]. Whether those limitations are
relevant to these specifications is an open question. It may be relevant to these specifications is an open question. It may be
simply another case of the considerable flexibility accorded to simply another case of the considerable flexibility accorded to
delivery MTAs in determining the mailbox names they will accept and delivery MTAs in determining the mailbox names they will accept and
how they are interpreted. how they are interpreted.
10.6. Non-Standard Encapsulation Formats 11.6. Non-Standard Encapsulation Formats
Some applications use formats similar to the application/mbox format Some applications use formats similar to the application/mbox format
defined in [RFC4155] instead of the message/digest form described in defined in [RFC4155] instead of the message/digest form described in
RFC 2046, Section 5.1.5 [RFC2046] to transfer multiple messages as RFC 2046, Section 5.1.5 [RFC2046] to transfer multiple messages as
single units. Insofar as such applications assume that all stored single units. Insofar as such applications assume that all stored
messages use the message/rfc822 format described in RFC 2046, Section messages use the message/rfc822 format described in RFC 2046, Section
5.2.1 [RFC2046] with US-ASCII message headers, they are not ready for 5.2.1 [RFC2046] with US-ASCII message headers, they are not ready for
the extensions specified in this series of documents and special the extensions specified in this series of documents and special
measures may be needed to properly detect and process them. measures may be needed to properly detect and process them.
11. IANA Considerations 12. IANA Considerations
This overview description and framework document does not contemplate This overview description and framework document does not contemplate
any IANA registrations or other actions. Some of the documents in any IANA registrations or other actions. Some of the documents in
the group have their own IANA considerations sections and the group have their own IANA considerations sections and
requirements. requirements.
12. Security Considerations 13. Security Considerations
Any expansion of permitted characters and encoding forms in email Any expansion of permitted characters and encoding forms in email
addresses raises some risks. There have been discussions on so addresses raises some risks. There have been discussions on so
called "IDN-spoofing" or "IDN homograph attacks". These attacks called "IDN-spoofing" or "IDN homograph attacks". These attacks
allow an attacker (or "phisher") to spoof the domain or URLs of allow an attacker (or "phisher") to spoof the domain or URLs of
businesses. The same kind of attack is also possible on the local businesses. The same kind of attack is also possible on the local
part of internationalized email addresses. It should be noted that part of internationalized email addresses. It should be noted that
the proposed fix involving forcing all displayed elements into the proposed fix involving forcing all displayed elements into
normalized lower-case works for domain names in URLs, but not email normalized lower-case works for domain names in URLs, but not email
local parts since those are case sensitive. local parts since those are case sensitive.
skipping to change at page 19, line 11 skipping to change at page 19, line 46
interprets such a message differently than the MUA used by the interprets such a message differently than the MUA used by the
recipient, then it may be possible to create a message that appears recipient, then it may be possible to create a message that appears
acceptable under the filter's interpretation but should be rejected acceptable under the filter's interpretation but should be rejected
under the interpretation given to it by that MUA. Such attacks under the interpretation given to it by that MUA. Such attacks
already exist for existing messages and encoding layers, e.g., already exist for existing messages and encoding layers, e.g.,
invalid MIME syntax, invalid HTML markup, and invalid coding of invalid MIME syntax, invalid HTML markup, and invalid coding of
particular image types. particular image types.
In addition, email addresses are used in many contexts other than In addition, email addresses are used in many contexts other than
sending mail, such as for identifiers under various circumstances sending mail, such as for identifiers under various circumstances
(see Section 10.2). Each of those contexts will need to be (see Section 11.2). Each of those contexts will need to be
evaluated, in turn, to determine whether the use of non-ASCII forms evaluated, in turn, to determine whether the use of non-ASCII forms
is appropriate and what particular issues they raise. is appropriate and what particular issues they raise.
This work will clearly affect any systems or mechanisms that are This work will clearly affect any systems or mechanisms that are
dependent on digital signatures or similar integrity protection for dependent on digital signatures or similar integrity protection for
email message headers (see also the discussion in Section 10.3). email message headers (see also the discussion in Section 11.3).
Many conventional uses of PGP and S/MIME are not affected since they Many conventional uses of PGP and S/MIME are not affected since they
are used to sign body parts but not message headers. On the other are used to sign body parts but not message headers. On the other
hand, the developing work on domain keys identified mail (DKIM) hand, the developing work on domain keys identified mail (DKIM)
[RFC5863] will eventually need to consider this work and vice versa: [RFC5863] will eventually need to consider this work and vice versa:
while this specification does not address or solve the issues raised while this specification does not address or solve the issues raised
by DKIM and other signed header mechanisms, the issues will have to by DKIM and other signed header mechanisms, the issues will have to
be coordinated and resolved eventually if the two sets of protocols be coordinated and resolved eventually if the two sets of protocols
are to co-exist. In addition, to the degree to which email addresses are to co-exist. In addition, to the degree to which email addresses
appear in PKI (Public Key Infrastructure) certificates, standards appear in PKI (Public Key Infrastructure) certificates, standards
addressing such certificates will need to be upgraded to address addressing such certificates will need to be upgraded to address
these internationalized addresses. Those upgrades will need to these internationalized addresses. Those upgrades will need to
address questions of spoofing by look-alikes of the addresses address questions of spoofing by look-alikes of the addresses
themselves. themselves.
13. Acknowledgments 14. Acknowledgments
This document is an update to, and derived from, RFC 4952. This This document is an update to, and derived from, RFC 4952. This
document would have been impossible without the work and document would have been impossible without the work and
contributions acknowledged in it. The present document benefited contributions acknowledged in it. The present document benefited
significantly from discussions in the EAI WG and elsewhere after RFC significantly from discussions in the EAI WG and elsewhere after RFC
4952 was published, especially discussions about the experimental 4952 was published, especially discussions about the experimental
versions of other documents in the internationalized email versions of other documents in the internationalized email
collection, and from RFC errata on RFC 4952 itself. collection, and from RFC errata on RFC 4952 itself.
Special thanks are due to Ernie Dainow for careful reviews and Special thanks are due to Ernie Dainow for careful reviews and
suggested text in this version. suggested text in this version.
14. References 15. References
14.1. Normative References 15.1. Normative References
[ASCII] American National Standards Institute [ASCII] American National Standards Institute
(formerly United States of America (formerly United States of America
Standards Institute), "USA Code for Standards Institute), "USA Code for
Information Interchange", ANSI X3.4-1968, Information Interchange", ANSI X3.4-1968,
1968. 1968.
ANSI X3.4-1968 has been replaced by newer ANSI X3.4-1968 has been replaced by newer
versions with slight modifications, but the versions with slight modifications, but the
1968 version remains definitive for the 1968 version remains definitive for the
skipping to change at page 20, line 38 skipping to change at page 21, line 26
[RFC5322] Resnick, P., Ed., "Internet Message [RFC5322] Resnick, P., Ed., "Internet Message
Format", RFC 5322, October 2008. Format", RFC 5322, October 2008.
[RFC5335bis-Hdrs] Yang, A. and S. Steele, "Internationalized [RFC5335bis-Hdrs] Yang, A. and S. Steele, "Internationalized
Email Headers", July 2010, <https:// Email Headers", July 2010, <https://
datatracker.ietf.org/doc/ datatracker.ietf.org/doc/
draft-ietf-eai-rfc5335bis/>. draft-ietf-eai-rfc5335bis/>.
[RFC5336bis-SMTP] Yao, J. and W. Mao, "SMTP Extension for [RFC5336bis-SMTP] Yao, J. and W. Mao, "SMTP Extension for
Internationalized Email Address", Internationalized Email Address",
June 2010, <https://datatracker.ietf.org/ August 2010, <https://datatracker.ietf.org/
doc/draft-ietf-eai-rfc5336bis/>. doc/draft-ietf-eai-rfc5336bis/>.
[RFC5337bis-DSN] Not yet posted?, "Internationalized [RFC5337bis-DSN] Not yet posted?, "Internationalized
Delivery Status and Disposition Delivery Status and Disposition
Notifications", Unwritten waiting for I-D, Notifications", Unwritten waiting for I-D,
2010. 2010.
[RFC5721bis-POP3] Not yet posted?, "POP3 Support for UTF-8", [RFC5721bis-POP3] Not yet posted?, "POP3 Support for UTF-8",
Unwritten waiting for I-D, 2010. Unwritten waiting for I-D, 2010.
skipping to change at page 21, line 17 skipping to change at page 22, line 5
and Document Framework", RFC 5890, and Document Framework", RFC 5890,
June 2010. June 2010.
[RFCNNNNbis-MailingList] Not yet posted?, "Mailing Lists and [RFCNNNNbis-MailingList] Not yet posted?, "Mailing Lists and
Internationalized Email Addresses", First Internationalized Email Addresses", First
Version still not in RFC Editor queue https Version still not in RFC Editor queue https
://datatracker.ietf.org/doc/ ://datatracker.ietf.org/doc/
draft-ietf-eai-mailinglist/, draft-ietf-eai-mailinglist/,
Unwritten waiting for I-D, 2010. Unwritten waiting for I-D, 2010.
14.2. Informative References 15.2. Informative References
[EAI-MUA-issues] EAI WG, "Still-unnamed proposed document on
MUA issues", Not assigned or agreed to yet,
2011.
Note to IESG and RFC Editor: While there is
provision for a document on this subject in
the WG Charter, there is, as yet, no plan
for producing it or even for adding it to
the WG's task list with benchmarks. If the
present document is approved for
publication before the is at least a title
and author(s) for an I-D, the citation and
reference should simply be dropped.
[EAI-Mailinglist] Gellens, R., "Mailing Lists and [EAI-Mailinglist] Gellens, R., "Mailing Lists and
Internationalized Email Addresses", Internationalized Email Addresses",
March 2010, <https://datatracker.ietf.org/ June 2010, <https://datatracker.ietf.org/
doc/draft-ietf-eai-mailinglist/>. doc/draft-ietf-eai-mailinglist/>.
[IAB-idn-encoding] Thaler, D., Klensin, J., and S. Cheshire, [IAB-idn-encoding] Thaler, D., Klensin, J., and S. Cheshire,
"IAB Thoughts on Encodings for "IAB Thoughts on Encodings for
Internationalized Domain Names", 2010, <htt Internationalized Domain Names", 2010, <htt
ps://datatracker.ietf.org/doc/ ps://datatracker.ietf.org/doc/
draft-iab-idn-encoding/>. draft-iab-idn-encoding/>.
[RFC0821] Postel, J., "Simple Mail Transfer
Protocol", STD 10, RFC 821, August 1982.
[RFC1123] Braden, R., "Requirements for Internet [RFC1123] Braden, R., "Requirements for Internet
Hosts - Application and Support", STD 3, Hosts - Application and Support", STD 3,
RFC 1123, October 1989. RFC 1123, October 1989.
[RFC1939] Myers, J. and M. Rose, "Post Office [RFC1939] Myers, J. and M. Rose, "Post Office
Protocol - Version 3", STD 53, RFC 1939, Protocol - Version 3", STD 53, RFC 1939,
May 1996. May 1996.
[RFC2033] Myers, J., "Local Mail Transfer Protocol", [RFC2033] Myers, J., "Local Mail Transfer Protocol",
RFC 2033, October 1996. RFC 2033, October 1996.
skipping to change at page 26, line 13 skipping to change at page 27, line 20
on review of the new text. on review of the new text.
o Removed references to the pre-EAI documents that were cited for o Removed references to the pre-EAI documents that were cited for
historical context in 4952. historical context in 4952.
o Got rid of a remaining pointer to address downgrading in the o Got rid of a remaining pointer to address downgrading in the
discussion of an updated MAILTO URI. discussion of an updated MAILTO URI.
o Minor additional editorial cleanups and tuning. o Minor additional editorial cleanups and tuning.
A.3. Changes between -02 and -03
o Inserted paragraph clarifying the status of the UTF8SMTPbis
keyword as a result of discussion prior to and during IETF 79.
o Adjusted some references including adding an explicit citation of
RFC 821.
o Removed the discussion of the experimental work from an inline
aside to a separate section, Section 6.
o Rewrote the discussion of configuration errors in MX setups to
make it clear that they are an issue with forward-pointing
addresses only and improved the discussion of backward-pointing
addresses.
o Removed some now-obsolete placeholder notes and resolved the
remaining one to a dangling reference.
Authors' Addresses Authors' Addresses
John C KLENSIN John C KLENSIN
1770 Massachusetts Ave, #322 1770 Massachusetts Ave, #322
Cambridge, MA 02140 Cambridge, MA 02140
USA USA
Phone: +1 617 491 5735 Phone: +1 617 491 5735
EMail: john-ietf@jck.com EMail: john-ietf@jck.com
YangWoo KO YangWoo KO
ICU ICU
119 Munjiro 119 Munjiro
Yuseong-gu, Daejeon 305-732 Yuseong-gu, Daejeon 305-732
Republic of Korea Republic of Korea
EMail: yw@mrko.pe.kr EMail: yw@mrko.pe.kr
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