Internet Draft: Mailing Lists and Internationalized R. Gellens
Email Addresses Qualcomm
Document: draft-ietf-eai-mailinglist-01.txt E. Chung
Expires: July 2007 Afilias
January 2007
Mailing Lists and Internationalized Email Addresses
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Copyright (C) The IETF Trust (2007). All Rights Reserved.
Abstract
This document describes considerations for mailing lists with the
introduction of internationalized email addressing capabilities.
Different scenarios involving interaction between mailing lists and
internationalized email addresses are examined. Furthermore,
mailing list header fields are discussed.
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This document makes specific recommendations on how mailing lists
should act in various situations.
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Table of Contents
1 Conventions Used in this Document . . . . . . . . . . . . . . 3
2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Scenarios Involving Mailing Lists . . . . . . . . . . . . . 4
4 Mailing List Header Fields . . . . . . . . . . . . . . . . 6
5 Managing Mailing Lists with Internationalized Email Address 6
6 Further Discussion . . . . . . . . . . . . . . . . . . . . 7
7 IANA Considerations . . . . . . . . . . . . . . . . . . . . 8
8 Security Considerations . . . . . . . . . . . . . . . . . . 8
9 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
10 Normative References . . . . . . . . . . . . . . . . . . . . 8
11 Informative References . . . . . . . . . . . . . . . . . . . 9
12 Author's Address . . . . . . . . . . . . . . . . . . . . . . 9
Appendix A: Changes from Previous Version . . . . . . . . . . 10
Intellectual Property Statement . . . . . . . . . . . . . . . 9
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 10
13 Copyright Statement . . . . . . . . . . . . . . . . . . . . -1
1 Conventions Used in this Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEYWORDS].
2 Introduction
Mailing lists are an important part of email usage and collaborative
communications. The introduction of internationalized email
addresses must take into consideration the impact on mailing list
functionality. The consideration of mailing lists in the context of
internationalized email addresses includes three main areas: (1)
transport protocol; (2) message headers; and (3) mailing list
operation policies.
A mailing list is a mechanism whereby a message may be distributed
to multiple recipients by sending to one recipient address. An
agent (typically not a human being) at that single address then
causes the message to be redistributed to the target recipients.
This agent sets the envelope return address of the redistributed
message to a different address from that of the original single
recipient message. Using a different envelope return address
(reverse-path) causes error (and other automatically generated)
messages to go to an error handling address associated with the
mailing list. (This avoids having error and other automatic messages
go to the original sender, who typically doesn't control the list
and hence can't do anything about them.)
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Some mailing lists alter the message header, while others do not. A
number of standardized list-related header fields have been defined,
and many lists add these headers. Separate from these standardized
list-specific header fields, and despite a history of
interoperability problems from doing so, some lists alter or add
header fields in an attempt to control where replies are sent. Such
lists typically add or replace the "Reply-To" field and some add or
replace the "Sender" field. Poorly-behaved lists may alter or
replace other fields, including "From".
While the mail transport protocol does not differ between regular
email accounts and mailing list accounts, lists have special
considerations with internationalized email addresses because they
retransmit to potentially many recipients messages composed by other
agents. Discussion of the different scenarios involving mailing
lists and internationalized email addresses is in Section 3.
Internationalized email address considerations arise in the
return-path as well as header fields of redistributed messages.
Among these header fields are those specified in RFC2369 -- The Use
of URLs as Meta-Syntax for Core Mail List Commands and their
Transport through Message Header Fields [RFC2369] and RFC2919 --
List-Id: A Structured Field and Namespace for the Identification of
Mailing Lists [RFC2919]. This will be described in Section 4.
With mailing lists, there are two different types of considerations:
first, the purely technical ones involving message handling, error
cases, downgrades, and the like, and second, those that arise from
the fact that humans use mailing lists to communicate. As an
example of the first, mailing lists may choose to reject all
messages from internationalized addresses that lack an alt-address.
As an example of the second, a user who sends a message to a list
often is unaware of the list membership. In particular, the user
often doesn't know if the members are i18mail users or not, and
often neither the original sender nor the recipients personally know
each other. As a consequence of this, remedies that may be readily
available may not be appropriate when dealing with mailing lists.
For example, if a user sends a message which is undeliverable, the
user can often use the telephone, IM, or other forms of
communication to obtain a working address. With mailing lists, the
users may not have any recourse.
A brief discussion on some key considerations for mailing list
operation in an internationalized email address environment is
proposed in Section 5. This is followed by further discussions in
Section 6.
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3 Scenarios Involving Mailing Lists
Expanding from Sections 2.3 ("i18mail mailing list") and 2.6 ("An
i18mail user sends to a mailing list with a mix of users") of the
Scenarios document [EAI- Scenarios], this section will provide an
overview of the different scenarios involving mailing lists and
internationalized email addresses.
What is worth noting is that generally, for mailing lists, the
original message is sent to the mailing list agent as a completely
separate and independenet transaction from the mailing list agent
sending the retransmitted message to one or more list recipients.
In each case, the message might have only one recipient, or might
have multiple recipients. That is, the original message might be
sent to additional recipients as well as the mailing list agent, and
the mailing list might choose to send the retransmitted message to
each list recipient in a separate SMTP transaction, or might choose
to include multiple recipients per transaction. (Often, mailing
lists are constructed to work in cooperation with, rather than
include the functionality of, an SMTP server, and hence the list
transmits to a single SMTP server one copy of the retransmitted
message, with all list recipients specified in the SMTP envelope.)
As the mailing list is sending out to its members, its MTA may
encounter a situation where a downgrade [EAI-Downgrade] may be
called for. In order for a downgrade to be possible, the mailing-
list (and/or its MTA) must therefore have the alt-address. In
general, it may be prudent for mailing list operators to pre-obtain
an alt-address for all its internationalized member addresses. This
will ensure that mailing list transactions within members will be
able to be delivered and replied to. Further discussion on mailing
list policy considerations is included in section 5 of this
document.
In the specific case where a non-member with an internationalized
email address is sending to a mailing list, and that mailing list is
UTF8SMTP-aware, and the path to a constituent member calls for a
downgrade, the mailing list (and/or its MTA) may not have the alt-
address of the non-member's internationalized email address,
therefore failing to deliver the message to some members. To
protect against this, a UTF8SMTP-aware mailing list might prefer to
reject submissions from internationalized email addresses that lack
an alt-address.
(Note that in the situation is not unique to mailing lists. Mail
relays that are UTF8SMTP- aware will potentially encounter the same
situation.) Further discussions are included in section 6 of this
document.
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4 Mailing List Header Fields
A number of header fields specifically for mailing lists have been
introduced in RFC2369 and RFC2919. These include, for example:
List-Id: List Header Mailing List <list-header.nisto.com>
List-Help: <mailto:list@host.com?subject=help> (List Instructions)
List-Unsubscribe: <mailto:list@host.com?subject=unsubscribe>
List-Subscribe: <mailto:list@host.com?subject=subscribe>
List-Post: <mailto:list@host.com>
List-Owner: <mailto:listmom@host.com> (Contact Person for Help)
List-Archive: <mailto:archive@host.com?subject=index%20list>
As described in RFC2369, "The contents of the list header fields
mostly consist of angle-bracket ('<', '>') enclosed URLs, with
internal whitespace being ignored." [RFC2369] Whereas RFC2919
specifies that, "The list identifier will, in most cases, appear
like a host name in a domain of the list owner." [RFC2919]
By and large, the data contained in these mailing list header fields
are URLs which often contain email addresses. The same mechanism
should be used for these fields as with other fields specifically
discussed in the UTF8-Headers document [EAI-UTF8Headers]. Generally
therefore, for fields that contain an internationalized email
address, it could be expressed as a UTF8 string.
These fields might contain other URLs, such as HTTP. In these
cases, there are no EAI-specific considerations, since these
non-mail-related URLs are out of scope for internationalized email
documents, and have been addressed elsewhere, such as RFC3987
"Internationalized Resource Identifier (IRI)" [RFC3987].
Downgrading provisions should also follow the chosen mechanism based
on the Downgrading document [EAI-Downgrade].
Because the email addresses are expressed as "mailto" URLs, further
specifications for presentation and inclusion of alt-addresses as
well as other considerations may be necessary, other than simply
following RFC3987 "Internationalized Resource Identifier (IRI)"
[RFC3987] specifications. This will be further discussed in Section
6.
5 Managing Mailing Lists with Internationalized Email Address
Given the need potentially to deal with non-UTF8SMTP-aware MTAs in
the path of delivery for different members, it is advisable that
mailing list operators obtain an alt-address from each member with
an internationalized email address before adding the member.
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In consideration for consistent delivery to all members in a
mailing- list, a mailing list may want to consider rejecting (or
otherwise obtaining alt-address from) a non-member who is
interacting with the mailing list from an internationalized email
address. This is further discussed in Section 6.
Furthermore, operators should take caution to avoid setting up an
MTA that is UTF8SMTP-aware with a mailing list program that is non-
aware. This is especially important for mailing list programs that
are based on a mail client and not directly integrated into an MTA.
The reverse may be less harmful but nevertheless should also be
avoided.
6 Further Discussion
While generally speaking, mailing lists do not create a significant
additional burden to the deployment of internationalized email
address functionalities, the study in this document does uncover a
couple of relevant areas for further consideration. While neither
items is entirely unique to mailing lists, it is true that mailing
lists face additional complexity since they redistribute messages
composed by other agents. Hence, they may be asked to accept a
message with non-ASCII headers composed by a UTF8SMTP-aware user
agent, and redistribute it to i18mail and non-i18mail users via
systems that are not UTF8SMTP-aware.
1. Obtaining Downgrade Information -- for a mailing list, or mail
relay server for that matter, that is UTF8SMTP-aware, receiving mail
from an internationalized email address, the alt-address is not
required from the sending MTA for the transport to be complete.
Thereupon when the mailing list retransmits the message to its
members, it may encounter paths where a downgrade is called for. In
order to mitigate this situation, the mailing list may perhaps
decide to reject all incoming mail from an internationalized email
address that lacks an alt-address. Alternatively, it may be useful
to consider having a mechanism, such as an additional SMTP command,
for the receiving MTA (in this case the mailing list) to request the
alt- address. This may be useful in other scenarios as well,
especially those concerning multiple recipients.
2. Downgrading Considerations for mailto URLs -- downgrading
specifications may have to be specified particularly for mailto URLs
to take into consideration the presentation of alt-address. The
UTF8 Headers document [EAI-UTF8Headers] suggests including a
parameter within the angle brackets of an email address (e.g.,
"<non-ascii@domain <<alt-ascii@domain>>"). In the case of a mailto
URL, it may be possible to use the same mechanism, for example,
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"<mailto:non-ascii@example.tld<alt-ascii@domain>?subject=help" or
perhaps "<mailto:non-ascii@example.tld?subject=help,
alt-ascii@domain>", however this should be further studied. Other
places where an internationalized email address could appear in a
URL may also require further examination.
7 IANA Considerations
None.
8 Security Considerations
Security considerations are discussed in the Framework document
[EAI-Framework].
9 Acknowledgments
10 Normative References
[EAI-Framework] J. Klensin and Y. Ko, "Overview and Framework for
Internationalized Email", draft-ietf-eai-framework-00.txt, May 24,
2006
[EAI-Scenarios] H. Alvestrand, "Internationalized Email Addresses:
Scenarios",draft-ietf-eai-scenarios-00.txt , May 12, 2006
[EAI-SMTPEXT] J. Yao and W. Mao, "SMTP extension for
internationalized email address", draft-ietf-eai-smtpext-00.txt, May
12, 2006
[EAI-UTF8Headers] J. Yeh, "Internationalized Email Headers", draft-
ietf-eai-utf8headers-00.txt, May 30, 2006
[EAI-Downgrade] Y. YONEYA and K. Fujiwara, "Downgrading mechanism
for Internationalized eMail Address (IMA)",
draft-ietf-eai-downgrade- 00.txt, May 26, 2006
[RFC2369] G. Neufeld and J. Baer, "The Use of URLs as Meta-Syntax
for Core Mail List Commands and their Transport through Message
Header Fields", July 1998
[RFC2919] R. Chandhok and G. Wenger, "List-Id: A Structured Field
and Namespace for the Identification of Mailing Lists", March 2001
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[RFC3987] M. Duerst and M. Suignard,"Internationalized Resource
Identifiers (IRIs)", January 2005
11 Informative References
12 Author's Address
Randall Gellens
QUALCOMM Incorporated
5775 Morehouse Drive
San Diego, CA 92121
rg+ietf@qualcomm.com
Edmon Chung
Afilias
Suite 204, 4141 Yonge Street,
Toronto, Ontario,
Canada M2P 2A8
edmon@afilias.info
Appendix A: Changes from Previous Version
THIS SECTION TO BE REMOVED PRIOR TO PUBLICATION.
Changes made from version -00 to -01:
o Fixed SMTP envelope versus message header confusion.
o Fixed erroneous mailing list operation text.
o Removed references to ATOMIC.
o Removed unneeded scenarios.
o Added discussion of human considerations which arise with lists.
o Fixed some typos.
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Datatracker
draft-ietf-eai-mailinglist-01
Internet-Draft
