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 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright Notice 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. Gellens & Chung [Page 1] Expires July 2007 Internet Draft Mailing Lists and i18mail Addresses January 2007 This document makes specific recommendations on how mailing lists should act in various situations. Gellens & Chung [Page 2] Expires July 2007 Internet Draft Mailing Lists and i18mail Addresses January 2007 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.) Gellens & Chung [Page 3] Expires July 2007 Internet Draft Mailing Lists and i18mail Addresses January 2007 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. Gellens & Chung [Page 4] Expires July 2007 Internet Draft Mailing Lists and i18mail Addresses January 2007 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. Gellens & Chung [Page 5] Expires July 2007 Internet Draft Mailing Lists and i18mail Addresses January 2007 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-Help: (List Instructions) List-Unsubscribe: List-Subscribe: List-Post: List-Owner: (Contact Person for Help) List-Archive: 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. Gellens & Chung [Page 6] Expires July 2007 Internet Draft Mailing Lists and i18mail Addresses January 2007 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., ">"). In the case of a mailto URL, it may be possible to use the same mechanism, for example, Gellens & Chung [Page 7] Expires July 2007 Internet Draft Mailing Lists and i18mail Addresses January 2007 "?subject=help" or perhaps "", 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 Gellens & Chung [Page 8] Expires July 2007 Internet Draft Mailing Lists and i18mail Addresses January 2007 [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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This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Gellens & Chung [Page 10] Expires July 2007