HTTP/1.1 200 OK Date: Mon, 08 Apr 2002 23:12:38 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Thu, 28 May 1998 01:33:00 GMT ETag: "2e7f34-325f-356cbecc" Accept-Ranges: bytes Content-Length: 12895 Connection: close Content-Type: text/plain INTERNET-DRAFT Ravinder Chandhok draft-chandhok-listid-00.txt Geoffrey Wenger Expires: November 26, 1998 Within Technology, Inc. May 26, 1998 List-Id: A Structured Field and Namespace for the Identification of Mailing Lists Status of this Memo This document is an Internet-Draft. 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.'' To view the entire list of current Internet-Drafts, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Copyright Notice Copyright (C) The Internet Society 1998. All Rights Reserved. Abstract Software that handles electronic mailing list messages (servers and user agents) needs a way to reliably identify messages that belong to a particular mailing list. With the advent of list headers [LISTSPEC] it has become even more important to provide an identifier to use to identify a mailing list regardless of the particular host that serves as the list processor at any given time. The List-Id header provides a standard location for such an identifier. In addition, a namespace for list identifiers based on fully qualified domain names is described. This namespace is intended to guarantee uniqueness for list owners who require it, while allowing for a less rigorous namespace for experimental and personal use. By including the List-Id field, list servers can make it easier for mail clients to provide automated tools for users to perform list functions. The list identifier can serve as a key to make many automated processing tasks easier, and hence more widely available. 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 RFC 2119. 1. Introduction Internet mailing lists have evolved into fairly sophisticated forums for group communication and collaboration; however, corresponding changes in the underlying infrastructure have lagged behind. Recent proposals like [LISTSPEC] have expanded the functionality that the MUA can provide by providing more information in each message sent by the mailing list distribution software. In order to further automate (and make more accurate) the processing a software agent can do, there needs to be some unique identifier to use as an identifier for the mailing list. This identifier can be simply used for filter string matching, or it can be used in more sophisticated systems to uniquely identify messages as belonging to a particular mailing list independent of the particular host delivering the actual messages. This identifier can also act as a key into a database of mailing lists. 2. The List Identifier Syntax The list identifer will, in most cases, appear like a host name in the domain of the owner's choosing. In other words, the domain name system is being used to delegate namespace authority for list identifiers just as it has been used to distribute that authority for other internet resources. If an entity is the owner of a domain or subdomain, then it may create list identifiers in the namespace of that domain. It is important to note that it is perfectly acceptable for a list identifier to be completely independent of the domain name of the host machine servicing the mailing list. If the owner of the list does not have access and permission to a domain-based namespace, they MAY create unmanaged list identifiers in the special unmanaged domain "x". This would apply to personal user, or users unable to afford domain name registration fees. The owner of a mailing list MUST NOT generate list identifiers in any domain namespace for which they do not have administrative control or have prior approval. The syntax for a list identifier in ABNF [RFC2234] follows: list-id = #label "." list-id-namespace list-id-namespace = #domain-name | unmanaged-list-id-namespace unmanaged-list-id-namespace = "x" Where: #label is a domain name label (limited to 63 characters), see [RFC2181] #domain-name is a fully qualified domain name (FQDN) [RFC2181] In addition, a list identifier MUST NOT be longer than 255 octets in length, for future compatibility. 3. The List-Id Header Field This document presents a header field which will provide an identifier for an e-mail distribution list. This header SHOULD be included on all messages distributed by the list (including command responses to individual users), and on other messages where the message clearly applies to this particular distinct list. There MUST be no more than one of each field present in any given message. This field MUST only be generated by mailing list software, not end users. The contents of the List-Id header mostly consist of angle-bracket ('<', '>') enclosed identifier, with internal whitespace being ignored. MTAs MUST NOT insert whitespace within the brackets, but client applications should treat any such whitespace, that might be inserted by poorly behaved MTAs, as characters to ignore. The list header fields are subject to the encoding and character restrictions for mail headers as described in [RFC822]. The List-Id header may optionally include a description by including it as a "phrase" [DRUMS], usually before the angle-bracketed list identifier. The MUA MAY choose to use this description in its user interface. The syntax of the List-Id header follows: list-id-header = "List-ID:" [FWS] [phrase] "<" list-id ">" [CFWS] CRLF where phrase, quoted-string, FWS, CFWS and CRLF are as defined in [DRUMS]. Examples: List-Id: "List Header Mailing List" List-Id: List-Id: "Lena's Personal Joke List" List-Id: "An internal CMU List" <0Jks9449.cmu.edu> List-Id: <0Jks9449384848xyzzy.0598.x> 4. Persistence of List Identifiers Although the list identifier MAY be changed by the mailing list administrator this is not desirable. (Note that there is no disadvantage to changing the description portion of the List-Id header.) A MUA MAY not recognize the change to the list identifier because the MUA SHOULD treat a different list identifier as a different list. As such the mailing list administrator SHOULD avoid changing the list identifier even when the host serving the list changes. On the other hand, transitioning from an informal unmanaged-list-id-namespace to a domain namespace is an acceptable reason to change the list identifier. Also if the focus of the list changes sufficiently the administrator may wish to retire the previous list and it's associated identifier to start a new list reflecting the new focus. 5. Uniqueness of List Identifiers This proposal seeks to leverage the existing administrative process already in place for domain name allocation. In particular, we exploit the fact that domain name ownership creates a namespace that by definition can be used to create unique identifiers within the domain. In addition, there must be a mechanism for identification of mailing lists that are administrated by some entity without administrative access to a domain. In this case, general heuristics can be given to reduce the chance of collision, but it cannot be guaranteed. If a list owner requires a guarantee, they are free to register a domain name under their control. List-IDs not ending with ".x" MUST be globally unique in reference to all other mailing lists. List owners wishing to use the special "x" namespace for their list identifier SHOULD use the month and year (in the form MMYY) that they create the list identifier as a "subdomain" of the "x" domain. In addition, some portion of the list identifier should be a randomly generated string. Thus, list identifiers such as and <0Jks9449384848xyzzy.0598.x> conform to these guidelines, while and does not. In fact, a particular list owner with several lists may choose to use the same random number subdomain when generating list identifiers for each of the lists. List-IDs ending with ".x" are not guaranteed to be globally unique. 6. Operations on List Identifiers There is only one operation defined for list identifiers, that of case insensitive equality (See Section 3.4.7. CASE INDEPENDENCE [RFC822]). The sole use of a list identifier is to identify a mailing list, and the sole use of the List-Id header is to mark a particular message as belonging to that list. The comparison operation MUST ignore any part of the List-Id header outside of the angle brackets, the MUA MAY choose to inform the user if the descriptive name of a mailing list changes. 7. Supporting Nested Lists A list that is a sublist for another list in a nested mailing list hierarchy MUST NOT modify the List-Id header field. 8. Security Considerations There are very few new security concerns generated with this proposal. Message headers are an existing standard, designed to easily accommodate new types. There may be concern with headers being forged, but this problem is inherent in Internet e-mail, not specific to the header described in this document. Further, the implications are relatively harmless. Mail list processors should not allow any user-originated List-Id fields to pass through to their lists, lest they confuse the user and have the potential to create security problems. On the client side, a forged list identifier may break automated processing. The list identifier (in its current form) should never be used as an indication of the authenticity of the message. 9. Acknowledgements The numerous participants of the List-Header [LISTHEADER] and ListMom-Talk [LISTMOM] mailing lists contributed much to the formation and structure of this document. Grant Neufeld focused much of the early discussion, and thus was essential in the creation of this document. References [RFC822] David H. Crocker, "Standard for the Format of ARPA Internet Text Messages" RFC 822, August 1982. [RFC2181] Elze, R., Bush, R. "Clarifications to the DNS Specification", RFC 2181, July 1997. [RFC2234] D. Crocker, P. Overell. "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [LISTSPEC] Grant Neufeld and Joshua D. Baer, "The Use of URLs as Meta-Syntax for Core Mail List Commands and their Transport through Message Header Fields" 'work in progress', February 1998. [DRUMS] P. Resnick, Editor, "Internet Message Format Standard", March 13 1998. [LISTHEADER] "List-Header" Mail list. list-header@list.nisto.com [LISTMOM] "ListMom-Talk" Mail list. listmom-talk@skyweyr.com Editors' addresses Ravinder Chandhok Within Technology, Inc. RD#1 Box 228 Waynesburg PA 15370 USA Email: chandhok@within.com Web: http://www.within.com/~chandhok Geoffrey Wenger Within Technology, Inc. RD#1 Box 228 Waynesburg PA 15370 USA Email: wenger@within.com Web: http://www.within.com/~wenger draft-chandhok-listid-00.txt Expires: November 26, 1998