Internet Draft: Mailing Lists and Internationalized R. Gellens Email Addresses Qualcomm Document: draft-ietf-eai-mailinglist-02.txt E. Chung Expires: January 2008 Afilias July 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 January 2008 Internet Draft Mailing Lists and i18mail Addresses July 2007 This document makes specific recommendations on how mailing lists should act in various situations. Gellens & Chung [Page 2] Expires January 2008 Internet Draft Mailing Lists and i18mail Addresses July 2007 Table of Contents 1 Conventions Used in this Document . . . . . . . . . . . . . . 3 2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Scenarios Involving Mailing Lists . . . . . . . . . . . . . 5 3.1 Pure Case Scenarios . . . . . . . . . . . . . . . . . . 6 3.2 Mixed Case Scenarios . . . . . . . . . . . . . . . . . . 7 4 Capabilities and Requirements . . . . . . . . . . . . . . . 8 5 List Header Fields . . . . . . . . . . . . . . . . . . . . . 9 6 List Management . . . . . . . . . . . . . . . . . . . . . 10 7 Further Discussion . . . . . . . . . . . . . . . . . . . . . 11 8 IANA Considerations . . . . . . . . . . . . . . . . . . . . 12 9 Security Considerations . . . . . . . . . . . . . . . . . . 12 10 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 12 11 Normative References . . . . . . . . . . . . . . . . . . . . 12 12 Informative References . . . . . . . . . . . . . . . . . . . 12 13 Author's Address . . . . . . . . . . . . . . . . . . . . . . 13 Appendix A: Changes from Previous Version . . . . . . . . . . 14 Intellectual Property Statement . . . . . . . . . . . . . . . 13 Full Copyright Statement . . . . . . . . . . . . . . . . . . 14 14 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 affects mailing lists in three main areas: (1) transport (receiving and sending messages); (2) message headers of received and retransmitted messages; and (3) mailing list operational policies. A mailing list is a mechanism whereby a message may be distributed to multiple recipients by sending to one address. An agent (typically not a human being) at that single address receives the message and then causes the message to be redistributed to a list of recipients. This agent sets the envelope return address of the redistributed message to a different address from that of the original message. Using a different envelope return address (reverse-path) directs error (and other automatically generated) messages to an error handling address associated with the mailing list. (This avoids having error and other automatic messages go to Gellens & Chung [Page 3] Expires January 2008 Internet Draft Mailing Lists and i18mail Addresses July 2007 the original sender, who typically doesn't control the list and hence can't do anything about them.) In most cases, the mailing list agent redistributes a received message to its subscribers as a new message, that is, conceptually it uses message submission [submit] (as did the sender of the original message). The exception, where the mailing list is not a separate agent that receives and redistributes messages in separate transactions, but is instead an expansion step within an SMTP transaction where one local address expands to multiple local or non-local addresses, is out of scope for this document. 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 one or more of 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". Among these list-specific 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 [List-*] and RFC2919 -- List-Id: A Structured Field and Namespace for the Identification of Mailing Lists [List-ID]. For more information, see Section 5. While the mail transport protocol does not differ between regular email recipients and mailing list recipients, lists have special considerations with internationalized email addresses because they retransmit messages composed by other agents to potentially many recipients. Discussion of the different scenarios involving mailing lists and internationalized email addresses is in Section 3. There are considerations for internationalized email addresses in the envelope as well as header fields of redistributed messages. In particular, an internationalized message cannot be downgraded unless envelope addresses are in ASCII (which includes use of ALT-ADDRESS). 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 might choose to reject all messages from internationalized addresses that lack an alt-address, or even all internationalized messages that can not be downgraded. As an example of the second, a user who sends a message to a list Gellens & Chung [Page 4] Expires January 2008 Internet Draft Mailing Lists and i18mail Addresses July 2007 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 for one-to-one communication might not be appropriate when dealing with mailing lists. For example, if a user sends a message which is undeliverable, normally the telephone, instant messaging, or other forms of communication are available to obtain a working address. With mailing lists, the users may not have any recourse. Of course, with mailing lists, the original sender usually does not know if the message was successfully received by any list members, or if it was undeliverable to some. Conceptually, a mailing list's internationalization can be divided into three capabilities: First, does it have a UTF8 submission address? Second, does it accept subscriptions to UTF8 addresses? And third, does it accept UTF8SMTP messages? This is explored in Section 4. A brief discussion on some key considerations for mailing list operation in an internationalized email address environment is proposed in Section 6. This is followed by further discussions in Section 7. 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 (and exclusively within the scope of this document) the original message is sent to a mailing list as a completely separate and independent transaction from the mailing list agent sending the retransmitted message to one or more list recipients. In both cases, 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 message submission 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, a message submission server, and hence the list transmits to a single submission server one copy of the retransmitted message, with all list recipients specified in the SMTP envelope. The submission server then decides which recipients to include in which Gellens & Chung [Page 5] Expires January 2008 Internet Draft Mailing Lists and i18mail Addresses July 2007 transaction.) [[[EDITOR'S NOTE: Is there any value to the text starting here?]]] The following diagram summarizes the conceptual working of a mailing- list (Pure Case): (b) -----> User1@exmaple.tld (a) / (c) User1@example.tld ------> mailing@list.tld ------> User2@example.tld \ (d) -----> ... As observed above, the mail transport transactions (a), (b), (c) and (d) all involves two parties, that is: 1. The mailing list agent; and, 2. The original author / subscriber. These scenarios are essentially the same as those already described in Sections 2.1 and 2.4 of the Scenarios document [EAI-Scenarios]. Multiple recipients are involved when additional addresses are included (Mixed Case): -----> User1@exmaple.tld (a) / User1@example.tld ---+--> mailing@list.tld ------> User2@example.tld | ^ \ (d) | | -----> ... | | | v | (e) | cc@example.tld <-----+-------------(reply)--+ Under this situation, scenarios (a) and (e) resemble the situations already described in Sections 2.2 and 2.5 of the Scenarios document [EAI-Scenarios]. More specific discussions based on these two general cases are included below. 3.1 Pure Case Scenarios In the Pure Case described above, the following are possible for (a): User1@example.tld mailing@list.tld (1) ASCII ASCII (2) non-ASCII ASCII Gellens & Chung [Page 6] Expires January 2008 Internet Draft Mailing Lists and i18mail Addresses July 2007 (3) ASCII non-ASCII (4) non-ASCII non-ASCII Among this set, (1) is simply the conventional case without involving any internationalized email address. (2) and (3) are scenarios described in Section 2.4 -- One i18nmail user sends to one ASCII user -- of the Scenarios document, whereas (4) is described in Section 2.1 -- Two i18nmail users [EAI-Scenarios]. For (d) -- generalizing (b) and (c) -- it may be branched further where: (i) Mailing list contains only ASCII email addresses (ii) Mailing list contains at least one internationalized email address [[[EDITOR'S NOTE: Is there any value to the text ending here?]]] The retransmitted message sent by the mailing list to its subscribers might need to be downgraded [EAI-Downgrade]. In order for a downgrade to be possible, the return path set by the mailing list agent must be an ASCII address or have ALT-ADDRESS specified. 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 6 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 7 of this document. [[[EDITOR'S NOTE: Is there any value to the text starting here?]]] 3.2 Mixed Case Scenarios Gellens & Chung [Page 7] Expires January 2008 Internet Draft Mailing Lists and i18mail Addresses July 2007 The Mixed Case scenarios are essentially a combination of the discussion in section 3.1 above, plus those described in Section 3.2 -- Three i18nmail users -- and, Section 2.5 -- An i18mail user sends to one ascii user and one i18nmail user -- of the Scenarios [EAI- Scenarios] document. Similar issues arise with regards to members versus non-members, especially non-members with an internationalized email address, as discussed in the above section. [[[EDITOR'S NOTE: Is there any value to the text ending here?]]] 4 Capabilities and Requirements There are three primary internationalization capabilities of mailing lists: First, does it have a UTF8 submission address? Second, does it allow subscriptions from UTF8 addresses? And third, does it accept UTF8SMTP messages? In theory, any list can support any combination of these. In practice, only some offer any benefit. For example, neither allowing UTF8 addresses to subscribe, nor accepting UTF8SMTP messages, makes much sense without the other (an all-ASCII address might or might not be capable of receiving UTF8SMTP messages, but a UTF8 address of necessity needs to accept UTF8SMTP messages). Likewise, there is no real benefit to a list in using a UTF8 submission address unless it also accepts UTF8SMTP messages and permits UTF8 addresses to subscribe. However, requirements for lists can be discussed separately for each of the three capabilities. 1. If the list uses a UTF8 submission address, it SHOULD specify an alt-address for it. Clearly, it needs to sit behind a UTF8SMTP-enabled final-delivery SMTP server and delivery agent. The list's return-path address is usually separate from its submission address (so that delivery reports and other automatically-generated messages are not sent to the submission address). For reliability in receiving delivery status notifications, a list MAY choose to use an all-ASCII return-path even if it uses a UTF8 submission address. If the list does use a UTF8 return path, it MUST specify an alt-address (or else there is a high risk of being unable to receive non-delivery reports). Gellens & Chung [Page 8] Expires January 2008 Internet Draft Mailing Lists and i18mail Addresses July 2007 It follows that if a list uses a UTF8 submission (or return-path) address, then its MSA needs to support UTF8SMTP. There are also implications for the List-* headers (see below). 2. If it allows UTF8 addresses to subscribe, it MAY require an alt-address to be specified for each UTF8 subscriber. Naturally, if it permits UTF8 addresses to subscribe, it needs a mechanism to accept subscription requests from such addresses (preferably specified in the form >). Likewise, its MSA needs to support UTF8SMTP. 3. If it accepts UTF8SMTP messages, its MSA needs to support UTF8SMTP. 5 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." [List-*] Whereas RFC2919 specifies that, "The list identifier will, in most cases, appear like a host name in a domain of the list owner." [List-ID] These mailing list header fields contain URLs. The most common schemes are generally HTTP, HTTPS, mailto, and FTP. These header fields will need to be extended to support UTF8 addresses. Except for mailto, there are no EAI-specific considerations, since these URLs can use RFC3987 "Internationalized Resource Identifier (IRI)" [IRI]. Note that mailto is being updated in a separate effort (outside of EAI), in [mailto-bis]. 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 is preferable for it to be expressed as a UTF8 string. Gellens & Chung [Page 9] Expires January 2008 Internet Draft Mailing Lists and i18mail Addresses July 2007 [[[EDITOR'S NOTE: Does RFC 2369 need to be updated to permit the use of IRIs?]]] Downgrading provisions should also follow the mechanism in the downgrading document [EAI-Downgrade]. However, special provisions may be helpful for list-specific headers. In particular, when a List-* header contains a UTF8 mailto followed by an ASCII mailto, it may be advisable to copy and preserve the original header as usual, but also edit the header to remove the UTF8 address. [[[EDITOR'S NOTE: This needs to be vetted by the eai list, and if agreed, the eai-downgrade document adjusted, and if not, deleted from here.]]] For mailto URIs, an additional consideration is how to include an alternative ASCII address (alt-address) for a UTF8 address. The most consistent approach is to extend mailto to permit the same syntax for alt-address as is used in address header fields, that is, >. Until this is done, the existing ability to specify multiple URLs within each List-* header field provides a solution. [List-*] says: A list of multiple, alternate, URLs MAY be specified by a comma- separated list of angle-bracket enclosed URLs. The URLs have order of preference from left to right. The client application should use the left most protocol that it supports, or knows how to access by a separate application. When a UTF8 mailto is used in a List-* header field, an alt-address, if available, SHOULD immediately follow it. This is further discussed in Section 7. 6 List Management 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. [[[EDITOR's NOTE: This contradicts an assumption that the group has been operating under that the sender obviously won't use UTF8SMTP unless his or her MSA and outbound MTAs support it, the recipient won't use a UTF8 address unless his or her final-delivery MTA and delivery agent support UTF8SMTP, and hence downgrading is unlikely in the normal case of UTF8SMTP sender to UTF8SMTP recipient. Accordingly, perhaps this requirement should be deleted or weakened.]]] Gellens & Chung [Page 10] Expires January 2008 Internet Draft Mailing Lists and i18mail Addresses July 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 without specifying an alt-address. This is further discussed in Section 7. It is important that the final delivery MTA and delivery agent not deliver internationalized messages to a mailing list that is not capable of receiving and processing them. Such messages MUST be downgraded or rejected unless the list supports internationalized email. Since a mailing list's MSA needs to support UTF8SMTP in order for it to send internationalized messages (including otherwise ASCII messages to UTF8 addresses), a list MUST NOT accept subscriptions from UTF8 addresses nor accept UTF8SMTP messages unless its MSA supports UTF8SMTP or it is prepared and able to downgrade such messages. 7 Further Discussion While mailing lists do not create a significant additional burden to the deployment of internationalized email address functionalities, there are some specific areas that need to be considered when the operator of a mailing list or of a final delivery MTA that serves a mailing list upgrades to internationalized mail. 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 subscribers, it may encounter paths where a downgrade is called for. In order to mitigate this situation, the mailing list might perhaps decide to reject all incoming mail from an internationalized email address that lacks an alt-address. However, note that in general, downgrades are not expected to be the normal case. Gellens & Chung [Page 11] Expires January 2008 Internet Draft Mailing Lists and i18mail Addresses July 2007 2. Downgrading Considerations for mailto URLs -- UTF8 addresses in mailto links in List-* headers will be easier to downgrade if they contain an alt-address. 8 IANA Considerations None. 9 Security Considerations Security considerations are discussed in the Framework document [EAI-Framework]. 10 Acknowledgments TBD. 11 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 12 Informative References [mailto-bis] M. Duerst and L. Masinter, "The mailto URI scheme", draft-duerst-mailto-bis-xx (work in progress). Gellens & Chung [Page 12] Expires January 2008 Internet Draft Mailing Lists and i18mail Addresses July 2007 [List-*] 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 [List-ID] R. Chandhok and G. Wenger, "List-Id: A Structured Field and Namespace for the Identification of Mailing Lists", March 2001 [IRI] M. Duerst and M. Suignard,"Internationalized Resource Identifiers (IRIs)", January 2005 13 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 -01 to -02: o Significant changes throughout the document. Sorry. 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 14] Expires January 2008 Internet Draft Mailing Lists and i18mail Addresses July 2007 Gellens & Chung [Page 15] Expires January 2008