draft-ietf-eai-smtpext-00.txt   draft-ietf-eai-smtpext-01.txt 
Network Working Group J. Yao, Ed. Network Working Group J. Yao, Ed.
Internet-Draft W. Mao, Ed. Internet-Draft W. Mao, Ed.
Expires: November 13, 2006 CNNIC Expires: January 27, 2007 CNNIC
May 12, 2006 July 26, 2006
SMTP extension for internationalized email address SMTP extension for internationalized email address
draft-ietf-eai-smtpext-00.txt draft-ietf-eai-smtpext-01.txt
Status of this Memo Status of this Memo
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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 November 9, 2006. This Internet-Draft will expire on January 27, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
Internationalized eMail Address (IMA) includes two parts, the local Internationalized email address includes two parts, the local part
part and the domain part. The way email addresses are used by and the domain part. The way email addresses are used by protocols
protocols are different from the way domain names are used. The most are different from the way domain names are used. The most critical
critical difference is that emails are delivered through a chain of difference is that emails are delivered through a chain of peering
peering clients and servers while domain names are resolved by name clients and servers while domain names are resolved by name servers
servers by looking up their own tables. In addition to this, email by looking up their own tables. In addition to this, email transport
transport protocols SMTP and ESMTP provide a negotiation mechanism protocols SMTP and ESMTP provide a negotiation mechanism through
through which clients can make decisions for further processing. So which clients can make decisions for further processing. So
IMA is different from the internationalized domain name (IDN). IMA internationalized email address is different from the
can be solved by exploiting the negotiation mechanism while IDN can internationalized domain name (IDN). It can be solved by exploiting
not use the negotiation mechanism. So IMA should be solved in the the negotiation mechanism while IDN can not use the negotiation
mail transport-level using the negotiation mechanism, which is an 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 the use architecturally desirable approach. This document specifies the use
of SMTP extension for IMA delivery. It also mentions the backward of SMTP extension for internationalized email address delivery. It
compatible mechanism for downgrade procedure, as specified in an also mentions the backward compatible mechanism for downgrade
associated specification. The protocol proposed here is MTA-level procedure, as specified in an associated specification. The protocol
solution which is feasible, architecturally more elegant, and not as proposed here is MTA-level solution which is feasible,
difficult to deploy in relevant communities. architecturally more elegant, and not as difficult to deploy in
relevant communities.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Role of this specification . . . . . . . . . . . . . . . . 3 1.1. Role of this specification . . . . . . . . . . . . . . . . 3
1.2. Proposal Context . . . . . . . . . . . . . . . . . . . . . 3 1.2. Proposal Context . . . . . . . . . . . . . . . . . . . . . 3
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Mail Transport-level Protocol . . . . . . . . . . . . . . . . 4 2. Mail Transport-level Protocol . . . . . . . . . . . . . . . . 4
2.1. Framework for the Internationalization Extension . . . . . 4 2.1. Framework for the Internationalization Extension . . . . . 4
2.2. The Address Internationalization Service Extension . . . . 4 2.2. The Address Internationalization Service Extension . . . . 4
2.3. Extended Mailbox Address Syntax . . . . . . . . . . . . . 5 2.3. Extended Mailbox Address Syntax . . . . . . . . . . . . . 5
2.4. The ALT-ADDRESS and ATOMIC parameter . . . . . . . . . . . 6 2.4. The ALT-ADDRESS parameter . . . . . . . . . . . . . . . . 6
2.5. Additional ESMTP Changes and Clarifications . . . . . . . 8 2.5. The Suggestion of the Value of the ALT-ADDRESS
2.5.1. The Initial SMTP Exchange . . . . . . . . . . . . . . 8 parameter . . . . . . . . . . . . . . . . . . . . . . . . 7
2.5.2. Trace Fields . . . . . . . . . . . . . . . . . . . . . 8 2.6. Additional ESMTP Changes and Clarifications . . . . . . . 8
2.5.3. Mailing List Question . . . . . . . . . . . . . . . . 8 2.6.1. The Initial SMTP Exchange . . . . . . . . . . . . . . 8
2.5.4. Message Header Label . . . . . . . . . . . . . . . . . 8 2.6.2. Trace Fields . . . . . . . . . . . . . . . . . . . . . 8
2.6.3. Mailing List Question . . . . . . . . . . . . . . . . 9
2.6.4. Message Header Label . . . . . . . . . . . . . . . . . 9
2.6.5. POP and IMAP . . . . . . . . . . . . . . . . . . . . . 9
3. Potential problems . . . . . . . . . . . . . . . . . . . . . . 9 3. Potential problems . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Impact to IRI . . . . . . . . . . . . . . . . . . . . . . 9 3.1. Impact to IRI . . . . . . . . . . . . . . . . . . . . . . 9
3.2. POP and IMAP . . . . . . . . . . . . . . . . . . . . . . . 9 3.2. Impact to RFC 2476 and many email related RFC . . . . . . 9
3.3. Impact to RFC 2476 and many email related RFC . . . . . . 9 4. Implementation Advice . . . . . . . . . . . . . . . . . . . . 10
4. Implementation Advice . . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Security considerations . . . . . . . . . . . . . . . . . . . 10 6. Security considerations . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . . 10 8.1. Normative References . . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . . 12 8.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . . . . 15
1. Introduction 1. Introduction
1.1. Role of this specification 1.1. Role of this specification
An overview document [IMA-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 IMA transport delivery. definition of an SMTP extension [RFC1869] for the internationalized
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. Domain part of the email address has been internationalized
through IDNA [RFC3490]. But the local part of the email address through IDNA [RFC3490]. But the local part of the email address
still remains as non-internationalized. 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 IMA. SMTP servers, we need to upgrade SMTP server to be able to carry the
Since older SMTP servers and the mail-reading clients and other internationalized email address. Since older SMTP servers and the
systems that are downstream from them may not be prepared to handle mail-reading clients and other systems that are downstream from them
these extended addresses, an SMTP extension is specified to identify MAY not be prepared to handle these extended addresses, an SMTP
and protect the addressing mechanism. extension is specified to identify and protect the addressing
mechanism.
This specification describes a change to the email transport This specification describes a change to the email transport
mechanism that permits IMA in both the envelope and header fields of mechanism that permits non-ASCII address in both the envelope and
messages. The context for the change is described in [IMA-overview] header fields of messages. The context for the change is described
and the details of the header changes are described in [IMA- in [EAI-overview] and the details of the header changes are described
utf8header]. in [EAI-utf8header].
1.3. Terminology 1.3. Terminology
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
IMA overview [IMA-overview] or in [RFC2821] and [RFC2822]. EAI overview [EAI-overview] or in [RFC2821] and [RFC2822]. The terms
"ASCII address", "internationalized email address", "non-ASCII
address", "i18mail address", "UTF8SMTP", "message" and "mailing list"
are used with the definitions from the EAI overview document.
This document is being discussed on the IMA 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:
1. The name of the SMTP service extension is "Internationalized 1. The name of the SMTP service extension is "Internationalized
Email and Extensions"; Email and Extensions";
2. The EHLO keyword value associated with this extension is 2. The EHLO keyword value associated with this extension is
"IEmail"; "UTF8SMTP";
3. No parameter values are defined for this EHLO keyword value. In 3. No parameter values are defined for this EHLO keyword value. In
order to permit future (although unanticipated) extensions, the order to permit future (although unanticipated) extensions, the
EHLO response MUST NOT contain any parameters for that keyword. EHLO response MUST NOT contain any parameters for that keyword.
If a parameter appears, the SMTP client that is conformant to If a parameter appears, the SMTP client that is conformant to
this version of this specification MUST treat the ESMTP response this version of this specification MUST treat the ESMTP response
as if the IMA keyword did not appear. as if the "UTF8SMTP" keyword did not appear.
4. Two optional parameters are added to the SMTP MAIL and RCPT 4. An optional parameters is added to the SMTP MAIL and RCPT
commands. The first parameter is named as ALT-ADDRESS. The commands. The parameter is named as ALT-ADDRESS. The "ALT-
second is ATOMIC. The "ALT-ADDRESS" requires an all-ASCII ADDRESS" requires an all-ASCII address as a substitute for the
address as a substitute for the internationalized (UTF-8 coded) i18mail addresses that we call the primary address; you can learn
address that we call the primary address; you can learn more in more in [EAI-overview] or [EAI-downgrading]. The value of "ALT-
[IMA-overview] or [IMA-downgrading]. The value of "ALT-ADDRESS" ADDRESS" is set by the sender when MUA and the submit ion server
may be set by sender or be gotten by using some algorithmic have a communication.
transformation according to the value of "ATOMIC". The "ATOMIC"
has one of two values: y or n. The parameter "ATOMIC" is
designed to assert whether the address is atomic, which means
that the primary address(IMA) can be safely transformed or
converted to the respect ASCII email address via ACE (ASCII
Compatible Encoding) if the value is 'y' or not if the value is
'n'.
5. No additional SMTP verbs are defined by this extension. 5. No additional SMTP verbs are defined by this extension.
6. Servers offering this extension MUST provide support for, and 6. Servers offering this extension MUST provide support for, and
announce, the 8BITMIME extension [RFC1652]. announce, the 8BITMIME extension [RFC1652].
2.2. The Address Internationalization Service Extension 2.2. The Address Internationalization Service Extension
An SMTP Server that announces this extension MUST be prepared to An SMTP Server that announces this extension MUST be prepared to
accept a UTF-8 string [RFC3629] in any position in which RFC 2821 accept a UTF-8 string [RFC3629] in any position in which RFC 2821
specifies that a "mailbox" may appear. That string must be parsed specifies that a "mailbox" MAY appear. That string MUST be parsed
only as specified in RFC 2821, i.e., by separating the mailbox into only as specified in RFC 2821, i.e., by separating the mailbox into
source route, local part and domain part, using only the characters source route, local part and domain part, using only the characters
colon (U+003A), comma (U+002C), and at-sign (U+0040) as specified colon (U+003A), comma (U+002C), and at-sign (U+0040) as specified
there. Once isolated by this parsing process, the local part MUST be there. Once isolated by this parsing process, the local part MUST be
treated as opaque unless the SMTP Server is the final delivery MTA. treated as opaque unless the SMTP Server is the final delivery MTA.
Any domain names that are to be looked up in the DNS MUST be Any domain names that are to be looked up in the DNS MUST first be
processed into the form as specified in IDNA [RFC3490] by means of processed into the form as specified in IDNA [RFC3490] by means of
the ToASCII() operation unless they are already in that form. Any the ToASCII() operation unless they are already in that form. Any
domain names that are to be compared to local strings SHOULD be domain names that are to be compared to local strings SHOULD be
checked for validity and then MUST be compared as specified in checked for validity and then MUST be compared as specified in
section 3.4 of IDNA. section 3.4 of IDNA.
An SMTP Client that receives the IMA extension keyword MAY transmit a An SMTP Client that receives the UTF8SMTP extension keyword in
mailbox name as an internationalized string in UTF-8 form and MAY response to the "EHLO" command MAY transmit a mailbox name as an
send an internationalized mail header [IMA-utf8header]. It MAY internationalized string in UTF-8 form and MAY send an
transmit the domain part of that string in either punycode (derived internationalized mail header [EAI-utf8header]. It MAY transmit the
from the IDNA process) or UTF-8 form. If it sends the domain in domain part of that string in either punycode (derived from the IDNA
UTF-8 form, the original SMTP client SHOULD first verify that the process) or UTF-8 form. If it sends the domain in UTF-8 form, the
string is valid for a domain name according to IDNA rules. As original SMTP client SHOULD first verify that the string is valid for
required by RFC 2821, it MUST not attempt to parse, evaluate, or a domain name according to IDNA rules. As required by RFC 2821, it
transform the local part in any way if the IMA SMTP extension is MUST not attempt to parse, evaluate, or transform the local part in
offered by the server. If the IMA SMTP extension is not offered by any way if the UTF8SMTP SMTP extension is offered by the server. If
the Server, the SMTP Client MUST NOT transmit an internationalized the UTF8SMTP SMTP extension is not offered by the Server, the SMTP
address and MUST NOT transmit a mail body which contains Client MUST NOT transmit an internationalized address and MUST NOT
internationalized mail headers [IMA-utf8header]. Instead, it MUST transmit a mail body which contains internationalized mail headers
either return the message to the user as undeliverable or replace it [EAI-utf8header]. Instead, it MUST either return the message to the
with the alternate ASCII address. If it is replaced, the replacement user as undeliverable or replace it with the alternate ASCII address.
MUST be either the ASCII-only address specified with the ALT-ADDRESS If it is replaced, the replacement MUST be the ASCII-only address
parameter or with an address obtained from some algorithmic specified with the ALT-ADDRESS parameter.[EAI-downgrading].
conversions of the primary address that conforms to the syntax rules
of RFC 2821, which is defined in [IMA-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 as
Mailbox = Local-part "@" Domain Mailbox = Local-part "@" Domain
Local-part = Dot-string / Quoted-string Local-part = Dot-string / Quoted-string
; MAY be case-sensitive ; MAY be case-sensitive
skipping to change at page 6, line 11 skipping to change at page 6, line 6
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.
According to the description above, define the syntax of an IMA According to the description above, define the syntax of an
mailbox with ABNF [RFC4234] as internationalized email mailbox with ABNF [RFC4234] as
Mailbox = Local-part "@" Domain Mailbox = Local-part "@" Domain
Local-part = Dot-string / Quoted-string Local-part = Dot-string / Quoted-string
; MAY be case-sensitive ; MAY be case-sensitive
Dot-string = Atom *("." Atom) Dot-string = Atom *("." Atom)
Atom = 1*Ucharacter Atom = 1*Ucharacter
Ucharacter = atext / UTF8-2 / UTF8-3 / UTF8-4 Ucharacter = atext / UTF8-2 / UTF8-3 / UTF8-4
skipping to change at page 6, line 34 skipping to change at page 6, line 29
Quoted-string = DQUOTE *qcontent DQUOTE Quoted-string = DQUOTE *qcontent DQUOTE
Domain = (sub-domain 1*("." sub-domain)) / address-literal Domain = (sub-domain 1*("." sub-domain)) / address-literal
sub-domain = ULet-dig [ULdh-str] sub-domain = ULet-dig [ULdh-str]
ULet-dig = Let-dig / Non-ASCII ULet-dig = Let-dig / Non-ASCII
ULdh-str = *( ALPHA / DIGIT / "-" / Non-ASCII) ULet-dig ULdh-str = *( ALPHA / DIGIT / "-" / Non-ASCII) ULet-dig
Non-ASCII = UTF8-2 / UTF8-3 / UTF8-4 Non-ASCII = UTF8-2 / UTF8-3 / UTF8-4
; UTF-8 characters prohibited by nameprep
; MUST NOT be used.
Where "atext", "qcontent" and "DQUOTE" are defined in [RFC2822], Where "atext", "qcontent" and "DQUOTE" are defined in [RFC2822],
"Let-dig", "Ldh-str" and "address-literal" are defined in [RFC2821] "Let-dig", "Ldh-str" and "address-literal" are defined in [RFC2821]
and UTF8-2, UTF8-3 and UTF8-4 are defined in [RFC3629]. The value of and UTF8-2, UTF8-3 and UTF8-4 are defined in [RFC3629]. The value of
"Local-part" should pass Stringprep [RFC3454]; The value of "domain" "domain" SHOULD be verified with [RFC3490]; If failed, the email
should be verified with [RFC3490]; If failed, The value of "Local- address with that domain can not be regarded as the valid email
part" and "domain", the email address can not be regarded as the address.
valid email address.
2.4. The ALT-ADDRESS and ATOMIC parameter 2.4. The ALT-ADDRESS parameter
If the IMA extension is offered, the syntax of the SMTP MAIL and RCPT If the UTF8SMTP extension is offered, the syntax of the SMTP MAIL and
commands is extended to support both the optional "ALT-ADDRESS" and RCPT commands is extended to support the optional "ALT-ADDRESS"
"ATOMIC" parameter. parameter.
The "ALT-ADDRESS" requires an all-ASCII address, which may set by the The "ALT-ADDRESS" requires an all-ASCII address.
sender or some algorithmic transformation.
The ALT-ADDRESS parameter usage in the commands of "mail from" and
"rcpt to" is defined according to the definition of mail-parameters
in [RFC2821] below.
MAIL FROM:<reverse-path> [SP <mail-parameters> ] <CRLF>
RCPT TO:<forward-path> [ SP <rcpt-parameters> ] <CRLF>
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
esmtp-value is all-ASCII email address, and where the domain and
Mailbox are defined at section 2.3 of this document.
The use of the ALT-ADDRESS is specified below: If some involved SMTP
servers can not support UTF8SMTP capability and if the sender has
already set the ALT-ADDRESS value, the client SMTP server will use
this address as the email address when the SMTP server does 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
email is bounced due to the incapability of supporting UTF8SMTP, the
relative server should issue the response error code "5.3.3" defined
in [RFC3463] which means that System is not capable of selected
features, permanent failure.
2.5. The Suggestion of the Value of the ALT-ADDRESS parameter
The "ALT-ADDRESS" requires an all-ASCII address. There are two
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
email address.
Some may prefer transformed the non-ASCII address to the ASCII
Compatible Encoding(ACE) address as the value of the ALT-ADDRESS.
The big problem with applying an ACE to all local-parts is that the The big problem with applying an ACE to all local-parts is that the
sending or converting system doesn't know if there are some specific sending or converting system doesn't know if there are some specific
data or instructions embedded in the address that the ACE process data or instructions embedded in the address that the ACE process
would hide. Some SMTP servers may depend on these specific data or would hide. Some SMTP servers may depend on these specific data or
instructions to do some operations while the local parts applied with instructions to do some operations while the local parts applied with
ACE will lose or hide these data or instructions. SMTP [RFC2821] ACE will lose or hide these data or instructions. SMTP [RFC2821]
prohibits SMTP relays from converting local parts because the level prohibits SMTP relays from converting local parts because the level
of SMTP relays' knowledge on the structure of local parts is assumed of SMTP relays' knowledge on the structure of local parts is assumed
to be zero. However, we can raise the knowledge level by supplying to be zero. However, we can raise the knowledge level by supplying
additional information. Many human users' email addresses do not additional information. Many human users' email addresses do not
have any embedded structure processed by the final delivery MTA. In have any embedded structure processed by the final delivery MTA. In
that case, the sender can specify that these email addresses are safe that case, the sender can specify that these email addresses are safe
to be converted in predefined way. The final delivery SMTP server to be converted in predefined way. The final delivery SMTP server
can revert the addresses even though they are as in all ASCII form. can revert the addresses even though they are as in all ASCII form.
In such cases, a potential recipient might be able to tell someone to Unless the MUA or the submission server clearly knows that the non-
whom the address is given "it is ok, there is no embedded information ASCII address can be safely transformed into the all-ASCII address,
here and you can convert it to an ACE address without danger". If the non-ASCII address should not be transformed because transformed
the recipient says that, then if the sender can pass that assertion email address may cause some potential problems.
along to his or her own (originator) MTA and the MTA can pass it down
the line, then an MTA that needs to do downgrading would know that
ACE-encoding is safe. The "ATOMIC" parameter is designed for the
above aim. Transmission of local-parts of UTF-8 avoids having to
deal with the problem.
The use of the ALT-ADDRESS will be according to the following
priority if SMTP servers can not support IMA capability. If the
sender has already set the ALT-ADDRESS value in spite of the value of
ATOMIC, the client SMTP server will use this address as the email
address when the SMTP server does the subsequent operations. If the
ALT-ADDRESS value is not set by the sender but the value of ATOMIC is
'y', the sender SMTP server should apply some algorithmic
transformation such as punycode to the entire local part of IMA; IDNA
should also be applied to the domain part of IMA; these operations
will get an ASCII email address for the subsequent SMTP operations
related to the email address. If the ALT-ADDRESS value is not set by
the sender and the value of ATOMIC is 'n' which means that the local
part of IMA can not be converted to the ASCII email address safely,
the email must be bounced to the original sender.
The suggested algorithmic transformation is punycode if the value of This document suggests that the ALT-ADDRESS is set directly by the
ALT-ADDRESS is not set by sender and the value of ATOMIC is 'y' when sender; In default, the all-ASCII address can not be transformed.
SMTP servers can not support IMA. Since the prefix "xn--" had been
used for IDNA, it is better that other prefix such as "bq--" is used
for the local part of converted version of the primary address to
avoid the potential confusion.
2.5. Additional ESMTP Changes and Clarifications 2.6. Additional ESMTP Changes and Clarifications
The mail transport process involves addresses ("mailboxes") and The mail transport process involves addresses ("mailboxes") and
domain names in contexts in addition to the MAIL and RCPT commands domain names in contexts in addition to the MAIL and RCPT commands
and extended alternatives to them. In general, the rule is that, and extended alternatives to them. In general, the rule is that,
when RFC 2821 specifies a mailbox, this document expects UTF-8 to be when RFC 2821 specifies a mailbox, this document expects UTF-8 to be
used for the entire string; when RFC 2821 specifies a domain name, used for the entire string; when RFC 2821 specifies a domain name,
the name should be in punycode form if its raw form is non-ASCII. the name SHOULD be in punycode form if its raw form is non-ASCII.
The following subsections list and discuss all of the relevant cases. The following subsections list and discuss all of the relevant cases.
Support and use of this extension requires support for 8BITMIME. It Support and use of this extension requires support for 8BITMIME. It
means that 8BITMIME must be advertised by the IMA capability SMTP means that 8BITMIME MUST be advertised by the UTF8SMTP capability
server. SMTP server.
2.5.1. The Initial SMTP Exchange 2.6.1. 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 IMA until after it client cannot know whether the server supports UTF8SMTP until after
receives the response from EHLO, any domain names that appear in this it receives the response from EHLO, any domain names that appear in
dialogue, or in responses to EHLO, must be in hostname form, i.e., this dialogue, or in responses to EHLO, MUST be in hostname form,
internationalized ones must be in punycode form. i.e., internationalized ones MUST be in punycode form.
2.5.2. Trace Fields 2.6.2. Trace Fields
Internationalized domain names in Received fields must be transmitted Internationalized domain names in Received fields MUST be transmitted
in the punycode form. Addresses in "for" clauses need further in the punycode form. Addresses in "for" clauses need further
examination and might be treated differently depending on [IMA- examination and might be treated differently depending on [EAI-
utf8header]. The reasoning in the introductory portion of [IMA- utf8header]. The reasoning in the introductory portion of [EAI-
overview] strongly suggests that these addresses be in UTF-8 form, overview] strongly suggests that these addresses be in UTF-8 form,
rather than some specialized encoding. rather than some specialized encoding.
2.5.3. Mailing List Question 2.6.3. 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 IMA capability and un- notifications in all plausible combinations of UTF8SMTP capability
capability servers is still not clear. This is an issue, which we and un-capability servers is discussed and specified in the [EAI-
can delve into in detail in the future discussion. We will proposed mailing list].
the detail solution to it in another document, and do some
experiments to find the best solution to it.
2.5.4. Message Header Label
There is a hot discussion about message header label when SMTP
messages are transmitted on wire. How to identify them and
distinguish them from the normal message. Many referred the famous
"MIME-Version:1.0" as the example. In order to get the robustness in
the absence of context, we should consider the issue whether or not
we need a mechanism(such as self-label) or some indicator to
distinguish or recognize the format of a "stored" message: new
format(i.e. IMA compliant) or old one (i.e. RFC 822 compliant).
[Note in draft: The detail discussion of this issue will be available
in [IMA-utf8header].]
3. Potential problems
3.1. Impact to IRI 2.6.4. Message Header Label
The mailto: schema in IRI [RFC3987] may need to be modified when IMA The message header label MAY be used to identify and distinguish the
is standardized. i18mail message from the normal message when SMTP messages are
transmitted on wire. This issue is discussed and specified in [EAI-
utf8header].
3.2. POP and IMAP 2.6.5. 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 IMA 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]. [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 IMA for the retrieval of messages from a mail server. names based on i18mail for the retrieval of messages from a mail
server. This is discussed and specified in the [EAI-imap].
3.3. Impact to RFC 2476 and many email related RFC 3. Potential problems
The IMA protocol will impact on many email related RFC such as 3.1. Impact to IRI
The mailto: schema in IRI [RFC3987] MAY need to be modified when EAI
is standardized.
3.2. Impact to RFC 2476 and many email related RFC
The EAI protocol will impact on many email related RFC such as
Message Submission [RFC2476] and SMTP Service Extension for DSNs Message Submission [RFC2476] and SMTP Service Extension for DSNs
[RFC3461]. These protocol should be considered when implementing the [RFC3461]. These protocol SHOULD be considered when implementing the
IMA protocol. 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 certain of them MUST be quoted as specified
there. It is notable in an internationalization context that there there. It is notable in an internationalization context that there
is a long history on some systems of using overstruck ASCII is a long history on some systems of using overstruck ASCII
characters (a character, a backspace, and another character) within a characters (a character, a backspace, and another character) within a
quoted string to approximate non-ASCII characters. This form of quoted string 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 "IEmail" 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.
6. Security considerations 6. Security considerations
See the extended security considerations discussion in [IMA-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. Chung, Tony Finch.
8. References 8. References
8.1. Normative References 8.1. Normative References
[ASCII] American National Standards Institute (formerly United [ASCII] American National Standards Institute (formerly United
States of America Standards Institute), "USA Code for States of America Standards Institute), "USA Code for
Information Interchange", ANSI X3.4-1968, 1968. Information Interchange", ANSI X3.4-1968, 1968.
ANSI X3.4-1968 has been replaced by newer versions with ANSI X3.4-1968 has been replaced by newer versions with
slight modifications, but the 1968 version remains slight modifications, but the 1968 version remains
definitive for the Internet. definitive for the Internet.
[IMA-overview] [EAI-downgrading]
YONEYA, Y., Ed. and K. Fujiwara, Ed., "Downgrading
mechanism for Internationalized eMail Address (IMA)",
draft-ietf-eai-downgrade-00 (work in progress),
October 2005.
[EAI-imap]
Resnick, P. and C. Newman, "Considerations for IMAP in
Conjunction with Email Address Internationalization",
draft-ietf-eai-imap-utf8-00 (work in progress), May 2006.
[EAI-mailing list]
Chung, E., "Mailing Lists and Internationalized Email
Addresses", June 2006.
Forthcoming
[EAI-overview]
Klensin, J. and Y. Ko, "Overview and Framework for Klensin, J. and Y. Ko, "Overview and Framework for
Internationalized Email", draft-klensin-ima-framework-01 Internationalized Email", draft-ietf-eai-framework-01.txt
(work in progress), February 2006. (work in progress), June 2006.
[IMA-utf8header] [EAI-pop] Newman, C., "POP3 Support for UTF-8", June 2006, <http://
Klensin, J. and J. Yeh, "Transmission of Email Headers in www.ietf.org/internet-drafts/draft-ietf-eai-pop-00.txt>.
UTF-8 Encoding", draft-yeh-utf8headers-00 (work in
progress), October 2005. [EAI-utf8header]
Yeh, J., "Transmission of Email Headers in UTF-8
Encoding", draft-ietf-eai-utf8headers-00.txt (work in
progress), June 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.
[RFC1869] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D. [RFC1869] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D.
Crocker, "SMTP Service Extensions", STD 10, RFC 1869, Crocker, "SMTP Service Extensions", STD 10, RFC 1869,
November 1995. November 1995.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
skipping to change at page 11, line 39 skipping to change at page 12, line 20
April 2001. April 2001.
[RFC3454] Hoffman, P. and M. Blanchet, "Preparation of [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings ("stringprep")", RFC 3454, Internationalized Strings ("stringprep")", RFC 3454,
December 2002. December 2002.
[RFC3461] Moore, K., "Simple Mail Transfer Protocol (SMTP) Service [RFC3461] Moore, K., "Simple Mail Transfer Protocol (SMTP) Service
Extension for Delivery Status Notifications (DSNs)", Extension for Delivery Status Notifications (DSNs)",
RFC 3461, January 2003. RFC 3461, January 2003.
[RFC3463] Vaudreuil, G., "Enhanced Mail System Status Codes",
RFC 3463, January 2003.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)", "Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003. RFC 3490, March 2003.
[RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode
for Internationalized Domain Names in Applications for Internationalized Domain Names in Applications
(IDNA)", RFC 3492, March 2003. (IDNA)", RFC 3492, March 2003.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003. 4rev1", RFC 3501, March 2003.
skipping to change at page 12, line 13 skipping to change at page 12, line 45
10646", RFC 3629, November 2003. 10646", RFC 3629, November 2003.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005. Identifiers (IRIs)", RFC 3987, January 2005.
[RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005. Specifications: ABNF", RFC 4234, October 2005.
8.2. Informative References 8.2. Informative References
[IMA-downgrading]
YONEYA, Y. and K. Fujiwara, "Downgrade Mechanism for
Internationalized Email Address (IMA)",
draft-yoneya-ima-downgrade-00 (work in progress),
October 2005.
[Klensin-emailaddr] [Klensin-emailaddr]
Klensin, J., "Internationalization of Email Addresses", Klensin, J., "Internationalization of Email Addresses",
draft-klensin-emailaddr-i18n-03 (work in progress), draft-klensin-emailaddr-i18n-03 (work in progress),
July 2005. July 2005.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996. Bodies", RFC 2045, November 1996.
Authors' Addresses Authors' Addresses
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