draft-ietf-eai-smtpext-02.txt   draft-ietf-eai-smtpext-03.txt 
Network Working Group J. Yao, Ed. Network Working Group J. Yao, Ed.
Internet-Draft W. Mao, Ed. Internet-Draft W. Mao, Ed.
Intended status: Informational CNNIC Expires: August 16, 2007 CNNIC
Expires: April 26, 2007 October 23, 2006 February 12, 2007
SMTP extension for internationalized email address SMTP extension for internationalized email address
draft-ietf-eai-smtpext-02.txt draft-ietf-eai-smtpext-03.txt
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skipping to change at page 1, line 34 skipping to change at page 1, line 34
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This Internet-Draft will expire on April 26, 2007. This Internet-Draft will expire on August 16, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The IETF Trust (2007).
Abstract Abstract
Internationalized email address includes two parts, the local part Internationalized email address includes two parts, the local part
and the domain part. The ways email addresses are used by protocols and the domain part. The ways email addresses are used by protocols
are different from the ways domain names are used. The most critical are different from the ways domain names are used. The most critical
difference is that emails are delivered through a chain of peering difference is that emails are delivered through a chain of peering
clients and servers while domain names are resolved by name servers clients and servers while domain names are resolved by name servers
by looking up their own tables. In addition to this, email transport by looking up their own tables. In addition to this, email transport
protocols SMTP and ESMTP provide a negotiation mechanism through protocols SMTP and ESMTP provide a negotiation mechanism through
which clients can make decisions for further processing. So which clients can make decisions for further processing. This
internationalized email address is different from the document specifies the use of SMTP extension for internationalized
internationalized domain name (IDN). It can be solved by exploiting email address delivery. It also mentions the backward compatible
the negotiation mechanism while IDN can not use the negotiation mechanism for downgrade procedure, as specified in an associated
mechanism. So internationalized email address SHOULD be solved in specification.
the mail transport-level using the negotiation mechanism, which is an
architecturally desirable approach. This document specifies the use
of SMTP extension for internationalized email address delivery. It
also mentions the backward compatible mechanism for downgrade
procedure, as specified in an associated specification. The protocol
proposed here is MTA-level solution which is feasible,
architecturally more elegant, and not as difficult to deploy in
relevant communities.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Role of this specification . . . . . . . . . . . . . . . . 4 1.1. Role of this specification . . . . . . . . . . . . . . . . 3
1.2. Proposal Context . . . . . . . . . . . . . . . . . . . . . 4 1.2. Proposal Context . . . . . . . . . . . . . . . . . . . . . 3
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Mail Transport-level Protocol . . . . . . . . . . . . . . . . 5 2. Mail Transport-level Protocol . . . . . . . . . . . . . . . . 4
2.1. Framework for the Internationalization Extension . . . . . 5 2.1. Framework for the Internationalization Extension . . . . . 4
2.2. The Address Internationalization Service Extension . . . . 5 2.2. The Address Internationalization Service Extension . . . . 5
2.3. Extended Mailbox Address Syntax . . . . . . . . . . . . . 6 2.3. Extended Mailbox Address Syntax . . . . . . . . . . . . . 5
2.4. The ALT-ADDRESS parameter . . . . . . . . . . . . . . . . 7 2.4. The ALT-ADDRESS parameter . . . . . . . . . . . . . . . . 8
2.5. The Suggestion of the Value of the ALT-ADDRESS 2.5. The Suggestion of the Value of the ALT-ADDRESS
parameter . . . . . . . . . . . . . . . . . . . . . . . . 8 parameter . . . . . . . . . . . . . . . . . . . . . . . . 9
2.6. Body Parts and SMTP Extensions . . . . . . . . . . . . . . 9 2.6. Body Parts and SMTP Extensions . . . . . . . . . . . . . . 9
2.7. Additional ESMTP Changes and Clarifications . . . . . . . 9 2.7. Additional ESMTP Changes and Clarifications . . . . . . . 10
2.7.1. The Initial SMTP Exchange . . . . . . . . . . . . . . 10 2.7.1. The Initial SMTP Exchange . . . . . . . . . . . . . . 10
2.7.2. Trace Fields . . . . . . . . . . . . . . . . . . . . . 10 2.7.2. Message Retry . . . . . . . . . . . . . . . . . . . . 10
2.7.3. Mailing List Question . . . . . . . . . . . . . . . . 10 2.7.3. Trace Information . . . . . . . . . . . . . . . . . . 11
2.7.4. Message Header Label . . . . . . . . . . . . . . . . . 10 2.7.4. Mailing List Question . . . . . . . . . . . . . . . . 12
2.7.5. POP and IMAP . . . . . . . . . . . . . . . . . . . . . 10 2.7.5. Message Header Label . . . . . . . . . . . . . . . . . 12
2.7.6. SMTP Service Extension for DSNs . . . . . . . . . . . 11 2.7.6. POP and IMAP . . . . . . . . . . . . . . . . . . . . . 12
3. Potential problems . . . . . . . . . . . . . . . . . . . . . . 11 2.7.7. SMTP Service Extension for DSNs . . . . . . . . . . . 13
3.1. Impact to IRI . . . . . . . . . . . . . . . . . . . . . . 11 3. Potential problems . . . . . . . . . . . . . . . . . . . . . . 13
3.2. Impact to RFC 2476 and many email related RFC . . . . . . 11 3.1. Impact to IRI . . . . . . . . . . . . . . . . . . . . . . 13
4. Implementation Advice . . . . . . . . . . . . . . . . . . . . 11 3.2. Impact to RFC 2476 and many email related RFC . . . . . . 13
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 4. Implementation Advice . . . . . . . . . . . . . . . . . . . . 13
6. Security considerations . . . . . . . . . . . . . . . . . . . 12 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 6. Security considerations . . . . . . . . . . . . . . . . . . . 14
8. Change History . . . . . . . . . . . . . . . . . . . . . . . . 12 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. draft-ietf-eai-smtpext: Version 00 . . . . . . . . . . . . 12 8. Change History . . . . . . . . . . . . . . . . . . . . . . . . 14
8.2. draft-ietf-eai-smtpext: Version 01 . . . . . . . . . . . . 12 8.1. draft-ietf-eai-smtpext: Version 00 . . . . . . . . . . . . 14
8.3. draft-ietf-eai-smtpext: Version 02 . . . . . . . . . . . . 12 8.2. draft-ietf-eai-smtpext: Version 01 . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8.3. draft-ietf-eai-smtpext: Version 02 . . . . . . . . . . . . 15
9.1. Normative References . . . . . . . . . . . . . . . . . . . 13 8.4. draft-ietf-eai-smtpext: Version 03 . . . . . . . . . . . . 15
9.2. Informative References . . . . . . . . . . . . . . . . . . 15 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 9.1. Normative References . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16 9.2. Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . . . 19
1. Introduction 1. Introduction
Internationalized email address is different from the
internationalized domain name (IDN). It can be solved by exploiting
the negotiation mechanism while IDN can not use the negotiation
mechanism. So internationalized email address SHOULD be solved in
the mail transport-level using the negotiation mechanism, which is an
architecturally desirable approach. This document specifies a
protocol to solve the problem of internationalized email address
based on ESMTP. The protocol proposed here is MTA-level solution
which is feasible, architecturally elegant, and not as difficult to
be deployed in relevant communities.
1.1. Role of this specification 1.1. Role of this specification
An overview document [EAI-overview] specifies the requirements for, An overview document [EAI-overview] specifies the requirements for,
and components of, full internationalization of electronic mail. and components of, full internationalization of electronic mail.
This document specifies an element of that work, specifically the This document specifies an element of that work, specifically the
definition of an SMTP extension [RFC1869] for the internationalized definition of an SMTP extension [RFC1869] for the internationalized
email address transport delivery. email address transport delivery.
1.2. Proposal Context 1.2. Proposal Context
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 the email internationalize both the domain part and the local part of the email
address. Domain part of the email address has been internationalized address. The domain part of the email address has been
through IDNA [RFC3490]. But the local part of the email address internationalized through IDNA RFC 3490 [RFC3490]. But the local
still remains as non-internationalized. part of the email address still remains as non-internationalized.
The syntax of Internet email addresses is restricted to a subset of The syntax of Internet email addresses is restricted to a subset of
7-bit ASCII for the domain-part, with a less-restricted subset for 7-bit ASCII for the domain-part, with a less-restricted subset for
the local-part. These restrictions are specified in RFC 2821 the local-part. These restrictions are specified in RFC 2821
[RFC2821]. To be able to deliver internationalized email through [RFC2821]. To be able to deliver internationalized email through
SMTP servers, we need to upgrade SMTP server to be able to carry the SMTP servers, we need to upgrade SMTP server to be able to carry the
internationalized email address. Since older SMTP servers and the internationalized email address. Since the older SMTP servers, the
mail-reading clients and other systems that are downstream from them mail-reading clients and other systems that are downstream from them
MAY not be prepared to handle these extended addresses, an SMTP might not be prepared to handle these extended addresses, an SMTP
extension is specified to identify and protect the addressing extension is specified to identify and protect the addressing
mechanism. mechanism.
This specification describes a change to the email transport This specification describes a change to the email transport
mechanism that permits non-ASCII address in both the envelope and mechanism that permits non-ASCII address in both the envelope and
header fields of messages. The context for the change is described header fields of messages. The context for the change is described
in [EAI-overview] and the details of the header changes are described in [EAI-overview] and the details of the header changes are described
in [EAI-utf8header]. in [EAI-utf8header].
1.3. Terminology 1.3. Terminology
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The key words "MUST", "SHALL", "REQUIRED", "SHOULD", "RECOMMENDED", The key words "MUST", "SHALL", "REQUIRED", "SHOULD", "RECOMMENDED",
and "MAY" in this document are to be interpreted as described in RFC and "MAY" in this document are to be interpreted as described in RFC
2119 [RFC2119]. 2119 [RFC2119].
All specialized terms used in this specification are defined in the All specialized terms used in this specification are defined in the
EAI overview [EAI-overview] or in [RFC2821] and [RFC2822]. The terms EAI overview [EAI-overview] or in [RFC2821] and [RFC2822]. The terms
"ASCII address", "internationalized email address", "non-ASCII "ASCII address", "internationalized email address", "non-ASCII
address", "i18mail address", "UTF8SMTP", "message" and "mailing list" address", "i18mail address", "UTF8SMTP", "message" and "mailing list"
are used with the definitions from the EAI overview document. are used with the definitions from the EAI overview document.
This document defines only those syntax rules that are different from
those of the base email specifications [RFC2821][RFC2822] and, where
the earlier rules are upgraded or extended, gives them new names.
When the new rule is a small upgrade to the older one, it is
typically given a name starting with "u". Rules that are undefined
here may be found in the base email documents under the same names.
This document is being discussed on the EAI mailing list. See This document is being discussed on the EAI mailing list. See
https://www1.ietf.org/mailman/listinfo/ima for information about https://www1.ietf.org/mailman/listinfo/ima for information about
subscribing. The list's archive is at subscribing. The list's archive is at
http://www1.ietf.org/mail-archive/web/ima/index.html. http://www1.ietf.org/mail-archive/web/ima/index.html.
2. Mail Transport-level Protocol 2. Mail Transport-level Protocol
2.1. Framework for the Internationalization Extension 2.1. Framework for the Internationalization Extension
The following service extension is defined: The following service extension is defined:
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the UTF8SMTP SMTP extension is not offered by the Server, the SMTP the UTF8SMTP SMTP extension is not offered by the Server, the SMTP
Client MUST NOT transmit an internationalized address and MUST NOT Client MUST NOT transmit an internationalized address and MUST NOT
transmit a mail body which contains internationalized mail headers transmit a mail body which contains internationalized mail headers
[EAI-utf8header]. Instead, it MUST either return the message to the [EAI-utf8header]. Instead, it MUST either return the message to the
user as undeliverable or replace it with the alternate ASCII address. user as undeliverable or replace it with the alternate ASCII address.
If it is replaced, the replacement MUST be the ASCII-only address If it is replaced, the replacement MUST be the ASCII-only address
specified with the ALT-ADDRESS parameter.[EAI-downgrading]. specified with the ALT-ADDRESS parameter.[EAI-downgrading].
2.3. Extended Mailbox Address Syntax 2.3. Extended Mailbox Address Syntax
RFC 2821, section 4.1.2, defines the syntax of a mailbox as RFC 2821, section 4.1.2, defines the syntax of a mailbox entirely in
terms of ASCII characters, using the production for "Mailbox" and
Mailbox = Local-part "@" Domain those on which it depends.
Local-part = Dot-string / Quoted-string
; MAY be case-sensitive
Dot-string = Atom *("." Atom)
Atom = 1*atext
Quoted-string = DQUOTE *qcontent DQUOTE
Domain = (sub-domain 1*("." sub-domain)) / address-literal
sub-domain = Let-dig [Ldh-str]
The key changes made by this specification are, informally, to The key changes made by this specification are, informally, to
o Change the definition of "sub-domain" to permit either the o Change the definition of "sub-domain" to permit either the
definition above or a UTF-8 string representing a DNS label that definition above or a UTF-8 string representing a DNS label that
is conformant with IDNA [RFC3490]. That label MUST NOT contain is conformant with IDNA [RFC3490]. That label MUST NOT contain
the characters "@" or ".", even though those characters can the characters "@" or ".", even though those characters can
normally be inserted into a DNS label. normally be inserted into a DNS label.
o Change the definition of "Atom" to permit either the definition o Change the definition of "Atom" to permit either the definition
above or a UTF-8 string. That string MUST NOT contain any of the above or a UTF-8 string. That string MUST NOT contain any of the
ASCII characters (either graphics or controls) that are not ASCII characters (either graphics or controls) that are not
permitted in "atext"; it is otherwise unrestricted. permitted in "atext"; it is otherwise unrestricted.
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is conformant with IDNA [RFC3490]. That label MUST NOT contain is conformant with IDNA [RFC3490]. That label MUST NOT contain
the characters "@" or ".", even though those characters can the characters "@" or ".", even though those characters can
normally be inserted into a DNS label. normally be inserted into a DNS label.
o Change the definition of "Atom" to permit either the definition o Change the definition of "Atom" to permit either the definition
above or a UTF-8 string. That string MUST NOT contain any of the above or a UTF-8 string. That string MUST NOT contain any of the
ASCII characters (either graphics or controls) that are not ASCII characters (either graphics or controls) that are not
permitted in "atext"; it is otherwise unrestricted. permitted in "atext"; it is otherwise unrestricted.
According to the description above, define the syntax of an According to the description above, define the syntax of an
internationalized email mailbox with ABNF [RFC4234] as internationalized email mailbox with ABNF [RFC4234] as
uMailbox = uLocal-part "@" uDomain
; Replace Mailbox in RFC 2821, section 4.1.2
Mailbox = Local-part "@" Domain uLocal-part = uDot-string / uQuoted-string
Local-part = Dot-string / Quoted-string
; MAY be case-sensitive ; MAY be case-sensitive
; Replace Local-part in RFC 2821, section 4.1.2
Dot-string = Atom *("." Atom) uDot-string = uAtom *("." uAtom)
; Replace Dot-string in RFC 2821, section 4.1.2
Atom = 1*Ucharacter uAtom = 1*ucharacter
Ucharacter = atext / UTF8-2 / UTF8-3 / UTF8-4 ; Replace Atom in RFC 2821, section 4.1.2
Quoted-string = DQUOTE *qcontent DQUOTE ucharacter = atext / Non-ASCII
; Replace character in RFC 2821, section 4.1.2
; atext is defined in RFC 2822
; UTF8-2, UTF8-3 and UTF8-4 are defined in RFC 3629
Domain = (sub-domain 1*("." sub-domain)) / address-literal uQuoted-string = DQUOTE *uqcontent DQUOTE
sub-domain = ULet-dig [ULdh-str] ; Replace Quoted-string in RFC 2821, section 4.1.2
; DQUOTE is Double Quote defined in RFC 4234
ULet-dig = Let-dig / Non-ASCII uqcontent = qcontent / Non-ASCII
; qcontent is defined in RFC 2822, section 3.2.5
ULdh-str = *( ALPHA / DIGIT / "-" / Non-ASCII) ULet-dig uDomain = (sub-udomain 1*("." sub-udomain)) / address-literal
; Replace Domain in RFC 2821, section 4.1.2
; address-literal is defined in RFC2821 section 4.1.2
sub-udomain = uLet-dig [uLdh-str]
; Replace sub-domain in RFC 2821, section 4.1.2
uLet-dig = Let-dig / Non-ASCII
; Let-dig in the right of '=' is defined in RFC 2822
uLdh-str = *( ALPHA / DIGIT / "-" / Non-ASCII) uLet-dig
; Replace Ldh-str in RFC 2821, section 4.1.2
Non-ASCII = UTF8-2 / UTF8-3 / UTF8-4 Non-ASCII = UTF8-2 / UTF8-3 / UTF8-4
Where "atext", "qcontent" and "DQUOTE" are defined in [RFC2822], The value of "udomain" SHOULD be verified with [RFC3490]; If failed,
"Let-dig", "Ldh-str" and "address-literal" are defined in [RFC2821] the email address with that udomain can not be regarded as the valid
and UTF8-2, UTF8-3 and UTF8-4 are defined in [RFC3629]. The value of email address.
"domain" SHOULD be verified with [RFC3490]; If failed, the email
address with that domain can not be regarded as the valid email
address.
2.4. The ALT-ADDRESS parameter 2.4. The ALT-ADDRESS parameter
If the UTF8SMTP extension is offered, the syntax of the SMTP MAIL and If the UTF8SMTP extension is offered, the syntax of the SMTP MAIL and
RCPT commands is extended to support the optional "ALT-ADDRESS" RCPT commands is extended to support the optional esmtp-keyword "ALT-
parameter. ADDRESS", to specify the conditions under which the SMTP server may
use ALT-ADDRESS for the possible downgrading. If the ALT-ADDRESS
esmtp-keyword is used, it MUST have an associated esmtp-value (ALT-
ADDRESS-esmtp-value which is defined below) which requires an all-
ASCII email address.
The "ALT-ADDRESS" requires an all-ASCII address. Based on the definition of mail-parameters in [RFC2821], the ALT-
ADDRESS parameter usage in the commands of "mail from" and "rcpt to"
is defined below.
The ALT-ADDRESS parameter usage in the commands of "mail from" and "MAIL FROM:" SP <uReverse-path> [ SP <mail-parameters> ]<CRLF>
"rcpt to" is defined according to the definition of mail-parameters ; Update mail command in RFC 2821, section 3.3
in [RFC2821] below.
MAIL FROM:<reverse-path> [ SP <mail-parameters> ] <CRLF> "RCPT TO:" SP <uForward-path> [ SP <rcpt-parameters> ]<CRLF>
RCPT TO:<forward-path> [ SP <rcpt-parameters> ] <CRLF> ; Update rcpt command in RFC 2821, section 3.3
Mail-parameters = esmtp-param *(SP esmtp-param)
Rcpt-parameters = esmtp-param *(SP esmtp-param)
esmtp-param = esmtp-keyword ["=" esmtp-value]
esmtp-keyword = (ALPHA / DIGIT) *(ALPHA / DIGIT / "-")
esmtp-value = 1*(%d33-60 / %d62-127)
; any CHAR excluding "=", SP, and control characters
Reverse-path = Path
Forward-path = Path
Path = "<" [ A-d-l ":" ] Mailbox ">"
A-d-l = At-domain *( "," A-d-l )
; Note that this form, the so-called "source route",
; MUST BE accepted, SHOULD NOT be generated, and SHOULD be
; ignored.
At-domain = "@" domain
where the value of esmtp-keyword is "ALT-ADDRESS" and the value of uReverse-path = uPath
esmtp-value is all-ASCII email address, and where the domain and ; Replace Reverse-path in RFC 2821, section 4.1.2
Mailbox are defined at section 2.3 of this document.
uForward-path = uPath
; Replace Forward-path in RFC 2821, section 4.1.2
uPath = "<" [ uA-d-l ":" ] uMailbox ">"
; Replace Path in RFC 2821, section 4.1.2
uA-d-l = uAt-domain *( "," uA-d-l )
; Replace A-d-l in RFC 2821, section 4.1.2
uAt-domain = "@" udomain
; Replace At-domain in RFC 2821, section 4.1.2
; udomain is defined in section 2.3 of this document
ALT-ADDRESS-esmtp-value=Mailbox
; Mailbox is defined in RFC 2821, section 4.1.2
The use of the ALT-ADDRESS is specified below: If some involved SMTP The use of the ALT-ADDRESS is specified below: If some involved SMTP
servers can not support UTF8SMTP capability and if the sender has servers can not support UTF8SMTP capability and if the sender has
already set the ALT-ADDRESS value, the client SMTP server will use already set the ALT-ADDRESS value, the client SMTP server will use
this address as the email address when the SMTP server does the this address as the email address when the SMTP server does the
subsequent operations. If the ALT-ADDRESS value is not set by the subsequent operations. If the ALT-ADDRESS value is not set by the
sender, the email must be bounced to the original sender. If the sender, the email must be bounced to the original sender. If the
email is bounced due to the incapability of supporting UTF8SMTP, the email is bounced due to the incapability of supporting UTF8SMTP, the
relative server should issue the response error code "5.3.3" defined relative server should issue the response error code "5.3.3" defined
in [RFC3463] which means that System is not capable of selected in [RFC3463] which means that System is not capable of selected
features, permanent failure. features, permanent failure.
2.5. The Suggestion of the Value of the ALT-ADDRESS parameter 2.5. The Suggestion of the Value of the ALT-ADDRESS parameter
The "ALT-ADDRESS" requires an all-ASCII address. There are two The "ALT-ADDRESS" requires an all-ASCII address. There are two
alternative ways to set ALT-ADDRESS value: one is set by the sender alternative ways to set ALT-ADDRESS value: one is set by the sender
using the all-ASCII address, the other is set using the transformed using the all-ASCII address, the other is set using the transformed
email address. email address.
Some may prefer transformed the non-ASCII address to the ASCII Some may prefer transforming the non-ASCII address to the ASCII
Compatible Encoding(ACE) address as the value of the ALT-ADDRESS. Compatible Encoding(ACE) address as the value of the ALT-ADDRESS. A
The big problem with applying an ACE to all local-parts is that the significant obstacle with applying an ACE to all local-parts is that
sending or converting system doesn't know if there are some specific the sending or converting system doesn't know if there are some
data or instructions embedded in the address that the ACE process specific data or instructions embedded in the address that the ACE
would hide. Some SMTP servers may depend on these specific data or process would hide. Some SMTP servers may depend on these specific
instructions to do some operations while the local parts applied with data or instructions to do some operations while the local parts
ACE will lose or hide these data or instructions. SMTP [RFC2821] applied with ACE will lose or hide these data or instructions. SMTP
prohibits SMTP relays from converting local parts because the level [RFC2821] prohibits SMTP relays from converting local parts because
of SMTP relays' knowledge on the structure of local parts is assumed the level of SMTP relays' knowledge on the structure of local parts
to be zero. However, we can raise the knowledge level by supplying is assumed to be zero. However, we can raise the knowledge level by
additional information. Many human users' email addresses do not supplying additional information. Many human users' email addresses
have any embedded structure processed by the final delivery MTA. In do not have any embedded structure processed by the final delivery
that case, the sender can specify that these email addresses are safe MTA. In that case, the sender can specify that these email addresses
to be converted in the predefined way. The final delivery SMTP are safe to be converted in the predefined way. The final delivery
server can revert the addresses even though they are as in all ASCII SMTP server can revert the addresses even though they are as in all
form. Unless the MUA or the submission server clearly knows that the ASCII form. Unless the MUA or the submission server clearly knows
non-ASCII address can be safely transformed into the all-ASCII that the non-ASCII address can be safely transformed into the all-
address, the non-ASCII address should not be transformed because ASCII address, the non-ASCII address should not be transformed
transformed email address may cause some potential problems. because transformed email address may cause some potential problems.
This document suggests that the ALT-ADDRESS is set directly by the This document suggests that the ALT-ADDRESS is set directly by the
sender; In default, the all-ASCII address should not be gotten from sender; In default, the all-ASCII address should not be gotten from
the transformation of the non-ASCII address. the transformation of the non-ASCII address.
2.6. Body Parts and SMTP Extensions 2.6. Body Parts and SMTP Extensions
While this specification requires that servers support the 8BITMIME While this specification requires that servers support the 8BITMIME
extension [RFC1652] to ensure that servers have adequate handling extension [RFC1652] to ensure that servers have adequate handling
capability for 8-bit data and to avoid a number of complex encoding capability for 8-bit data and to avoid a number of complex encoding
skipping to change at page 10, line 19 skipping to change at page 10, line 37
2.7.1. The Initial SMTP Exchange 2.7.1. The Initial SMTP Exchange
When an SMTP or ESMTP connection is opened, the server sends a When an SMTP or ESMTP connection is opened, the server sends a
"banner" response consisting of the 220 reply code and some "banner" response consisting of the 220 reply code and some
information. The client then sends the EHLO command. Since the information. The client then sends the EHLO command. Since the
client cannot know whether the server supports UTF8SMTP until after client cannot know whether the server supports UTF8SMTP until after
it receives the response from EHLO, any domain names that appear in it receives the response from EHLO, any domain names that appear in
this dialogue, or in responses to EHLO, MUST be in hostname form, this dialogue, or in responses to EHLO, MUST be in hostname form,
i.e., internationalized ones MUST be in punycode form. i.e., internationalized ones MUST be in punycode form.
2.7.2. Trace Fields 2.7.2. Message Retry
Internationalized domain names in Received fields MUST be transmitted When an MSA or MTA encounters a server that doesn't support UTF8SMTP
in the punycode form. Addresses in "for" clauses need further while relaying a message that requires such support, it is
examination and might be treated differently depending on RECOMMENDED that an alternate MX be tried, and/or the message is
[EAI-utf8header]. The reasoning in the introductory portion of requeued for a later attempt, rather than immediately downgrading or
[EAI-overview] strongly suggests that these addresses be in UTF-8 bouncing. If the message is requeued, the total elapsed time before
form, rather than some specialized encoding. bouncing or downgrading SHOULD be smaller than the value used for
other SMTP error conditions such as host unreachable or persistent
4xx response codes.
2.7.3. Mailing List Question This alternate-MX-or-retry-later technique SHOULD NOT be used when
the message's return path is a non-ASCII address and the specific
forward path being attempted is an ASCII address (because the
implication that the delivery path normally supports UTF8SMTP does
not hold in this case).
The selection of submission servers is presumably under the control
of the sender's client, while the selection of potential intermediate
relays is under the control of the administration of the final
delivery server. Hence, there is a presumption, at least when the
recipient address is non-ASCII, that the delivery path servers
normally support UTF8SMTP (if the sender's client or MSA didn't
support UTF8SMTP, the message would not have been accepted for
delivery in the first place). Thus, a lack of UTF8SMTP support is
likely to be a temporary situation, such as a normal inbound server
being down and a cooperating site acting as a backup MX. If the lack
of UTF8SMTP in the delivery path of a message is a temporary
situation, and the message is sent successfully after retrying, then
it was a good thing to do. Of course, if there is always an ASCII-
only SMTP server in the path, then retrying only adds delay to the
failure (bounce or downgrade).
2.7.3. Trace Information
When an SMTP server receives a message for delivery or further
processing, it MUST insert trace ("time stamp" or "Received")
information at the beginning of the message content. The most
important use of Received: lines is for debugging mail faults. For
the trace information, we update the time stamp line and the return
path line [RFC2821] formally defined as follows:
uReturn-path-line = "Return-Path:" FWS uReverse-path <CRLF>
; Replaces Return-path-line in the section 4.4 of [RFC2821]
; uReverse-path is defined in Section 2.3
uTime-stamp-line = "Received:" FWS uStamp <CRLF>
; Replaces Time-stamp-line in the section 4.4 of [RFC2821]
uStamp = From-domain By-domain uOpt-info ";" FWS date-time
; Replaces Stamp in the section 4.4 of [RFC2821]
uOpt-info = [Via] [With] [ID] [uFor]
; Replaces Opt-info in the section 4.4 of [RFC2821]
; [With]'s protocl value will allow UTF8SMTP value
uFor = "FOR" FWS 1*( Path / uMailbox ) CFWS
; Replaces For in the section 4.4 of [RFC2821]
; uReverse-path is defined in Section 2.4
Except in the 'uFor' and 'uReverse-path' line where non-ASCII domain
name may be used, internationalized domain names in Received fields
MUST be transmitted in the punycode form. The [With]'s protocl value
will have the value of 'UTF8SMTP' for UTF8SMTP extension. We will
give more informaiton about this in "IANA consideration" section of
this document. If a "for" clause containing non-ASCII is encountered
when downgrading a message, it is better to just drop the "for"
clause rather than figure out some creative way to encode it. When
only the domain portion of a "for" clause address contains non-ASCII,
this document suggests using the punycode form of the domain portion.
For more detailed information, you may see it in [EAI-utf8header].
2.7.4. Mailing List Question
How a mixture of traditional and internationalized addresses on a How a mixture of traditional and internationalized addresses on a
mailing list will impact message flows, error reports, and delivery mailing list will impact message flows, error reports, and delivery
notifications in all plausible combinations of UTF8SMTP capability notifications in all plausible combinations of UTF8SMTP capability
and un-capability servers is discussed and specified in the and un-capability servers is discussed and specified in the
[EAI-mailing list]. [EAI-mailing list].
2.7.4. Message Header Label 2.7.5. Message Header Label
The message header label MAY be used to identify and distinguish the Today it is routine that many MTAs scan every message for spam, virus
i18mail message from the normal message when SMTP messages are or other reasons. It seems that few MTAs depend on "Header-Type"
transmitted on wire. This issue is discussed and specified in fields or marker to decide the message's type. The better choice is
[EAI-utf8header]. to rely on scanning the message to decide the message's type:
UTF8SMTP or ASCII, instead of the header label "Header-Type" fields
or marker. The message header label "Header-Type" SHOULD NOT be used
to identify and distinguish the i18mail message from the normal
message when SMTP messages are transmitted on wire. This issue is
discussed and specified in [EAI-utf8header].
2.7.5. POP and IMAP 2.7.6. POP and IMAP
While SMTP mainly takes care of the transportation of messages and While SMTP mainly takes care of the transportation of messages and
the header fields on wire, POP essentially handles the retrieval of the header fields on wire, POP essentially handles the retrieval of
mail objects from the server by a client. In order to use mail objects from the server by a client. In order to use
internationalized user names based on i18mail for the retrieval of internationalized user names based on i18mail for the retrieval of
messages from a mail server using the POP protocol, a new capability messages from a mail server using the POP protocol, a new capability
SHOULD be introduced following the POP3 extension mechanism SHOULD be introduced following the POP3 extension mechanism
[RFC2449]. This is discussed and specified in the [EAI-pop]. [RFC2449]. This is discussed and specified in the [EAI-pop].
IMAP [RFC3501] uses the traditional user name which is based on IMAP [RFC3501] uses the traditional user name which is based on
ASCII. IMAP SHOULD be updated to support the internationalized user ASCII. IMAP SHOULD be updated to support the internationalized user
names based on i18mail for the retrieval of messages from a mail names based on i18mail for the retrieval of messages from a mail
server. This is discussed and specified in the [EAI-imap]. server. This is discussed and specified in the [EAI-imap].
2.7.6. SMTP Service Extension for DSNs 2.7.7. SMTP Service Extension for DSNs
How to facilitate the use of SMTP Service Extension for DSNs The existing draft standard Delivery status notifications
[RFC3461] in the work of EAI will be addressed in the [EAI-dsn]. (DSNs)[RFC3461] is presently limited to US-ASCII text in the machine
readable portions of the protocol. "International Delivery and
Disposition Notifications" [EAI-dsn] adds a new address type for
international email addresses so an original recipient address with
non-US-ASCII characters can be correctly preserved even after
downgrading. If an SMTP server advertises both the UTF8SMTP and the
DSN extension, that server MUST implement EAI-dsn [EAI-dsn] including
support for the ORCPT parameter.
3. Potential problems 3. Potential problems
3.1. Impact to IRI 3.1. Impact to IRI
The mailto: schema in IRI [RFC3987] MAY need to be modified when EAI The mailto: schema in IRI [RFC3987] MAY need to be modified when EAI
is standardized. is standardized.
3.2. Impact to RFC 2476 and many email related RFC 3.2. Impact to RFC 2476 and many email related RFC
The EAI protocols will impact on many email related RFC documents The EAI protocols will impact on many email related RFC documents
such as Message Submission [RFC2476]. These protocols SHOULD be such as Message Submission [RFC2476]. These protocols SHOULD be
considered when implementing the EAI protocol. considered when implementing the EAI protocol.
4. Implementation Advice 4. Implementation Advice
In the absence of this extension, SMTP clients and servers are In the absence of this extension, SMTP clients and servers are
constrained to using only those addresses permitted by RFC 2821. The constrained to using only those addresses permitted by RFC 2821. The
local parts of those addresses MAY be made up of any ASCII local parts of those addresses MAY be made up of any ASCII
characters, although certain of them MUST be quoted as specified characters, although some of them MUST be quoted as specified there.
there. It is notable in an internationalization context that there It is notable in an internationalization context that there is a long
is a long history on some systems of using overstruck ASCII history on some systems of using overstruck ASCII characters (a
characters (a character, a backspace, and another character) within a character, a backspace, and another character) within a quoted string
quoted string to approximate non-ASCII characters. This form of to approximate non-ASCII characters. This form of
internationalization SHOULD be phased out as this extension becomes internationalization SHOULD be phased out as this extension becomes
widely deployed but backward-compatibility considerations require widely deployed but backward-compatibility considerations require
that it continue to be supported. that it continue to be supported.
5. IANA Considerations 5. IANA Considerations
IANA is requested to add "UTF8SMTP" to the SMTP extensions registry IANA is requested to add "UTF8SMTP" to the SMTP extensions registry
with the entry pointing to this specification for its definition. with the entry pointing to this specification for its definition.
The "Mail Transmission Types" registry is requested to be updated to
include the following new entries:
WITH protocol types Description Reference
------------------- ---------------------------- ---------
UTF8SMTP UTF8SMTP with Service Extensions [RFCxxxx]
UTF8SMTPA UTF8SMTP with SMTP AUTH [RFCxxxx]
UTF8SMTPS UTF8SMTP with STARTTLS [RFCxxxx]
UTF8SMTPSA UTF8SMTP with both STARTTLS and [RFCxxxx]
SMTP AUTH
6. Security considerations 6. Security considerations
See the extended security considerations discussion in [EAI-overview] See the extended security considerations discussion in [EAI-overview]
7. Acknowledgements 7. Acknowledgements
Much of the text in the initial version of this document was derived Much of the text in the initial version of this document was derived
or copied from [Klensin-emailaddr] with the permission of the author. or copied from [Klensin-emailaddr] with the permission of the author.
Significant comments and suggestions were received from Xiaodong LEE, Significant comments and suggestions were received from Xiaodong LEE,
Nai-Wen Hsu, Yangwoo KO, Yoshiro YONEYA, and other members of the JET Nai-Wen Hsu, Yangwoo KO, Yoshiro YONEYA, and other members of the JET
team and were incorporated into the document. Special thanks to team and were incorporated into the document. Special thanks to
those contributors for this version of document, those includes (but those contributors for this version of document, those includes (but
not limited to) John C Klensin, Charles Lindsey, Dave Crocker, Harald not limited to) John C Klensin, Charles Lindsey, Dave Crocker, Harald
Tveit Alvestrand, Marcos Sanz, Chris Newman, Martin Duerst, Edmon Tveit Alvestrand, Marcos Sanz, Chris Newman, Martin Duerst, Edmon
Chung, Tony Finch, Kari Hurtta. Chung, Tony Finch, Kari Hurtta, Randall Gellens.
8. Change History 8. Change History
[[anchor20: REMOVE THIS: This section is used for tracking the update [[anchor21: REMOVE THIS: This section is used for tracking the update
of this document. It may be useful to retain parts of it to of this document. It may be useful to retain parts of it to
facilitate establishing dates and documents for the history of this facilitate establishing dates and documents for the history of this
work.]] work.]]
8.1. draft-ietf-eai-smtpext: Version 00 8.1. draft-ietf-eai-smtpext: Version 00
This version supercedes draft-yao-ima-smtpext-03.txt. It refines the This version supercedes draft-yao-ima-smtpext-03.txt. It refines the
ABNF definiton of the internationalized email address. It represents ABNF definiton of the internationalized email address. It represents
as the EAI working group document. as the EAI working group document.
skipping to change at page 12, line 49 skipping to change at page 15, line 17
ADDRESS parameter". ADDRESS parameter".
8.3. draft-ietf-eai-smtpext: Version 02 8.3. draft-ietf-eai-smtpext: Version 02
o Upgraded to reflect the recent discussion of the ima@ietf.org o Upgraded to reflect the recent discussion of the ima@ietf.org
mailing list. mailing list.
o Add the section of "Body Parts and SMTP Extensions". o Add the section of "Body Parts and SMTP Extensions".
o Add the new section of "Change History". o Add the new section of "Change History".
o Add the subsection about SMTP extensions for DSN. o Add the subsection about SMTP extensions for DSN.
8.4. draft-ietf-eai-smtpext: Version 03
o Update the syntax related to mailbox.
o Update the trace field section.
o Add the new section about message retry.
o Update the subsection about SMTP extensions for DSN.
9. References 9. References
9.1. Normative References 9.1. Normative References
[ASCII] American National Standards Institute (formerly United [ASCII] Cerf, V., "ASCII format for network interchange", RFC 20,
States of America Standards Institute), "USA Code for October 1969.
Information Interchange", ANSI X3.4-1968, 1968.
ANSI X3.4-1968 has been replaced by newer versions with
slight modifications, but the 1968 version remains
definitive for the Internet.
[EAI-downgrading] [EAI-downgrading]
YONEYA, Y., Ed. and K. Fujiwara, Ed., "Downgrading YONEYA, Y., Ed. and K. Fujiwara, Ed., "Downgrading
mechanism for Internationalized eMail Address (IMA)", mechanism for Internationalized eMail Address (IMA)",
draft-ietf-eai-downgrade-02 (work in progress), draft-ietf-eai-downgrade-02 (work in progress),
August 2006. August 2006.
[EAI-dsn] Newman, C., "SMTP extensions for DSNs", 12 2006, <http:// [EAI-dsn] Newman, C., "SMTP extensions for DSNs",
www.ietf.org/internet-drafts/draft-ietf-eai-dsn-00.txt>. draft-ietf-eai-dsn-00.txt (work in progress), 1 2007.
[EAI-imap] [EAI-imap]
Resnick, P. and C. Newman, "Considerations for IMAP in Resnick, P. and C. Newman, "Considerations for IMAP in
Conjunction with Email Address Internationalization", Conjunction with Email Address Internationalization",
draft-ietf-eai-imap-utf8-00 (work in progress), May 2006. draft-ietf-eai-imap-utf8-00 (work in progress), May 2006.
[EAI-mailing list] [EAI-mailing list]
Chung, E., "Mailing Lists and Internationalized Email Gellens, R. and E. Chung, "Mailing Lists and
Addresses", June 2006. Internationalized Email Addresses",
draft-ietf-eai-mailinglist-01.txt (work in progress),
Forthcoming January 2007.
[EAI-overview] [EAI-overview]
Klensin, J. and Y. Ko, "Overview and Framework for Klensin, J. and Y. Ko, "Overview and Framework for
Internationalized Email", draft-ietf-eai-framework-02.txt Internationalized Email", draft-ietf-eai-framework-04.txt
(work in progress), October 2006. (work in progress), 12 2006.
[EAI-pop] Newman, C., "POP3 Support for UTF-8", June 2006, <http:// [EAI-pop] Newman, C., "POP3 Support for UTF-8",
www.ietf.org/internet-drafts/draft-ietf-eai-pop-00.txt>. draft-ietf-eai-pop-01.txt (work in progress),
January 2007.
[EAI-utf8header] [EAI-utf8header]
Yeh, J., "Transmission of Email Headers in UTF-8 Yeh, J., "Transmission of Email Headers in UTF-8
Encoding", draft-ietf-eai-utf8headers-01.txt (work in Encoding", draft-ietf-eai-utf8headers-01.txt (work in
progress), August 2006. progress), August 2006.
[RFC1652] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D. [RFC1652] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D.
Crocker, "SMTP Service Extension for 8bit-MIMEtransport", Crocker, "SMTP Service Extension for 8bit-MIMEtransport",
RFC 1652, July 1994. RFC 1652, July 1994.
skipping to change at page 16, line 7 skipping to change at page 19, line 7
Wei MAO (editor) Wei MAO (editor)
CNNIC CNNIC
No.4 South 4th Street, Zhongguancun No.4 South 4th Street, Zhongguancun
Beijing Beijing
Phone: +86 10 58813055 Phone: +86 10 58813055
Email: mao@cnnic.cn Email: mao@cnnic.cn
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2006). Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
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