Network Working Group Jacob Palme Internet Draft Stockholm University/KTH, Sweden draft-ietf-drums-MHRegistry-00.txt January 1997 Category: Informational Expires August 1997 Mail Header Registration Procedure 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 learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind, since this document is mainly a compilation of information taken from other RFCs.. Distribution of this memo is unlimited. Abstract Various IETF standards and e-mail software products use various e-mail header fields. This memo specifies a procedure for the registration of e-mail header field names, to reduce the risk that two different mail products use the same header name in different ways. A proposed initial content of the header name registry at start-up is specifed in an appendix to this ietf-draft. Table of contents 1. Introduction 2. Which Headers are Registered 3. Who can Register a Header Name 4. Registration Procedure 4.1 Present the Request for Registration to the Community 4.2 Submit the Header name to the IANA for Registration 5. Clarifications On Specific Issues 5.1 E-mail Requirements for a Limited Number of Headers 5.2 Header Status 5.3 Requirements for a Published Specification 5.4 Identification of Security Considerations 5.5 Recommendations and Standards Status 6. Security Considerations 7. Acknowledgments 8. References 9. Author's address 10. Appendix: Proposed initial content of the IETF header name registry Temporary comment (not to be included in the published RFC) The first version is based mainly on two previous documents: RFC 1590: Media registration draft-ietf-mailext-mail-attributes-07.txt This version will need more discussion on at least the following points: - Should every header get its own OID? Would this make conversion of Internet e-mail headers to X.400 eaier? - How much explanation should the header registry contain for each header? - Which are the allowed values of the status field in the registry? Differences between draft-palme-MHRegistry-00.txt and this revised version draft-ietf-drums-MHRegistry-00.txt: Two non-standard headers have been added in the appendix, "For-Comment" and "For-Handling". They are variants of "To:" which indicate what action this recipient is asked to perform when receiving this message. 1. Introduction Many different Internet standards, other RFCs and e-mail software products define headers which may occur on Internet mail messages and/or Usenet News articles. There is an obvious risk that the same header name is used in different ways by different software products. The solution proposed in RFC 822, to allow header names beginning with "X-" for non-standard header names has several drawbacks. One is that it does not preclude two different products using the same "X-" header name with different semantic meaning. Another is that if an "X-" header gets popular and much used, and is to become a standard, there is a problem with removing the "X-" in front of an already much used header. Because of this, an IANA registry for e-mail and Usenet News header field names is needed. The following words are used in this memo with the meaning specified below: heading Formatted text at the top of a message, ended by a blank line header = heading One field in the heading, beginning with a field header name, colon, and followed by the field value(s) 2. Which Headers are Registered The header name registry can contain headers from the following sources: - Internet standards - RFCs which are not Internet standards - Non-Internet standards - Other commonly used headers - Sometimes used headers whose use is discouraged. The use of a header name may be discouraged because it is badly defined, ambigous or used in different ways by different software. The purpose of registering discouraged headers is to avoid their use in their present or any other future semantic meaning. The registry is intended to contain headers used in messaging (e-mail, Usenet News, etc.) but not HTTP-only headers. 3. Who can Register a Header Name Header names from Internet standards are registered by IETF together with the standard specifying the header. Headers in other RFCs are registered when the RFCs are published. Anyone can propose the registry of additional headers, but such headers should be approved by the IETF application area managers before accepted in the registry. The procedure described in this memo is followed by the IANA for review and approval of new e-mail headers. This is not a formal standards process, but rather an administrative procedure intended to allow community comment and sanity checking without excessive time delay. 4. Registration Procedure 4.1 Present the Request for Registration to the Community Send a proposed header to the "firstname.lastname@example.org" mailing list. This mailing list has been established for the sole purpose of reviewing proposed e-mail headers. You can subscribe to the list by sending a message to email@example.com containing in the text a line with "subscribe mail-headers " followed by our name (not your e-mail address), and unsubscribe with a message "unsubscribe mail-headers". Archives of this list are available by anonymous FTP from ftp://segate.sunet.se/lists/mail-headers/ by HTTP from http://segate.sunet.se/archives/mail-headers.html by E-MAIL send a message to LISTSERV@SEGATE.SUNET.SE with the text "INDEX mail-headers" to get a list of the archive files, and then a new message "GET <file name>" to retrieve the archive files. The FTP and E-MAIL archives are best if you want to retrieval all messages during a month or more, while the HTTP archives are better if you want to browse and find particular messages to download. The intent of the public posting is to solicit comments and feedback on the choice of header name, the unambiguity of the references with respect to versions and external profiling information, the choice of which OIDs to use, and a review of the security considerations section. It should be noted that the proposed header name does not need to make sense for every possible application. If the header name is intended for a limited or specific use, this should be noted in the submission. 4.2 Submit the Header name to the IANA for Registration After at least two weeks, submit the proposed header to the IANA for registration. The request and supporting documentation should be sent to "firstname.lastname@example.org". Provided a reasonable review period has elapsed, the IANA will register the header, assign an OID under the IANA branch, and make the header registration available to the community. The header registrations will be posted in the anonymous FTP directory "ftp.isi.edu:in-notes/mail-headers" and the header will be listed in the periodically issued "Assigned Numbers" RFC . The header description may be published as an Informational RFC by sending it to "email@example.com" (please follow the instructions to RFC authors ). 5. Clarifications On Specific Issues 5.1 E-mail Requirements for a Limited Number of Headers Issue: In the asynchronous mail environment, where information on the capabilities of the remote mail agent is not available to the sender, maximum interoperability is attained by restricting the number of headers used to those "common" headers expected to be widely implemented. This was asserted as a reason to limit the number of possible headers and resulted in a registration process with a significant hurdle and delay for those registering headers. 5.2 Header Status Any header in the registry should be marked with a status, which has one of the values specified below: IETF standard. Specified in an IETF standard. IETF draft standard. Specified in an IETF draft standard. IETF proposed Specified in an IETF proposed standard. standard. IETF experimental Specified in an IETF experimental standard. standard. X.400. Used to mark headers which are defined in RFC 1327 for use in messages from or to Internet mail/X.400 gateways, and which have not been standardized for general usage in the exchange of messages between Internet mail-based systems. Usenet News only, De facto standard in Usenet News, may not in e-mail. occur in messages gatewayed from Usenet News to e-mail, no defined meaning in e-mail. Non-standard, only Used in Usenet News, may occur in in Usenet News, not messages gatewayed from Usenet News to in e-mail. e-mail, no defined meaning in e-mail. Usenet news only, De facto standard in Usenet News, may discouraged in occur in messages gatewayed from Usenet e-mail. News to e-mail, but such practice is discouraged. Not standardized for Used to mark headers defined only for use in e-mail. use in Usenet News. These headers have no standard meaning when appearing in e-mail, some of them may even be used in different ways by different software. When appearing in e-mail, they should be handled with caution. Other standard. Defined in standard developed by another standards making body than IETF. Non-standard. This header is not specified in any of the RFCs which define Internet protocols, including Internet Standards, Draft Standards, Proposed Standards and Experimental Standards. The header appears here because it often appears in e-mail or Usenet News. Usage of these headers is not in general recommended. Some header proposed in ongoing IETF standards development work, but not yet accepted, are also marked in this way. discouraged This header, which is non-standard or historical, is known to create problems and should not be generated. Handling of such headers in incoming mail should be done with great caution. controversial The meaning and usage of this header is controversial, i.e. different implementors have chosen to implement the header in different ways. Because of this, such headers should be handled with caution and understanding of the different possible interpretations. 5.3 Requirements for a Published Specification Issue: Header registration requires an RFC specifying the header, except for header names marked as discouraged in the header registry. The following information should be provided when applying for registry of a new e-mail or Usenet News header: - Header name. - Status, one of the statuses specified in section 5.2 above. - If the header is specified in an RFC, the number of this RFC. - If the header is specified in another standard than an RFC, a reference to this standard. - If the header is not specified in an RFC, a textual description should be enclosed, which describes the header, its intended use and discusses security considerations. 5.4 Identification of Security Considerations Issue: The registration process requires the identification of any known security problems with the header name. Comment: It is not required that the header be secure or that it be free from risks, but that the known risks be identified. Publication of a header name does not require an exhaustive security review, and the security considerations section is subject to continuing evaluation. Additional security considerations should be periodically published in an RFC by IANA. 5.5 Recommendations and Standards Status Issue: The registration of a header does not imply endorsement, approval, or recommendation by IANA or IETF or even certification that the specification is adequate. 6. Security Considerations This memo does not address specific security issues but outlines a security review process for headers 7. Acknowledgments Harald Tveit Alvestrand, Ned Freed, Olle Järnefors, Keith Moore, Nick Smith and several other people have helped me with compiling the list in the appendix. I alone take responsibility for any errors which may still be in the list. 8. References Ref. Author, title IETF status (July 1996) ---- ------------------------------------------ -------------  J. Postel: "Simple Mail Transfer Standard, Protocol", STD 10, RFC 821, August 1982. Recommended 2] D. Crocker: "Standard for the format of Standard, ARPA Internet text messages." STD 11, RFC Recommended 822, August 1982.  M.R. Horton, R. Adams: "Standard for Not an interchange of USENET messages", RFC 1036, offi-cial IETF December 1987. standard, but in reality a de-facto standard for Usenet News 4] M. Sirbu: "A Content-Type header for Standard, internet messages", RFC 1049, March 1988. Recommended, but can in the future be expected to be replaced by MIME 5] R. Braden (editor): "Requirements for Standard, Internet Hosts -- Application and Required Support", STD-3, RFC 1123, October 1989.  D. Robinson, R. Ullman: "Encoding Header Non-standard for Internet Messages", RFC 1154, April 1990.  S. Hardcastle-Kille: "Mapping between Proposed X.400(1988) / ISO 10021 and RFC 822", RFC standard, 1327 May 1992. elective 8] H. Alvestrand & J. Romaguera: "Rules for Proposed Downgrading Messages from X.400/88 to standard, X.400/84 When MIME Content-Types are elective Present in the Messages", RFC 1496, August 1993.  A. Costanzo: "Encoding Header for Internet Non-standard Messages", RFC 1154, April 1990. 10] A. Costanzo, D. Robinson: "Encoding Header Experimental for Internet Messages", RFC 1505, August 1993.  N. Borenstein & N. Freed: "MIME Draft Standard, (Multipurpose Internet Mail Extensions) elective Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1521, Sept 1993.  H. Alvestrand: "Tags for the Proposed Identification of Languages", RFC 1766, standard, February 1995. elective 13] J. Palme: "Electronic Mail", Artech House Non-standard publishers, London-Boston January 1995.  R. Troost, S. Dorner: "Communicating Experimental Presentation Information in Internet Messages: The Content-Disposition Header", RFC 1806, June 1995.  B. Kantor, P. Lapsley, "Network News Proposed Transfer Protocol: "A Proposed Standard standard for the Stream-Based Transmission of News", RFC 977, January 1986.  1848 PS S. Crocker, N. Freed, J. Proposed Galvin, S. Murphy, "MIME Object Security standard Services", RFC 1848, March 1995.  J. Myers, M. Rose: The Content-MD5 Header, Draft standard RFC 1864, October 1995.  M. Horton, UUCP mail interchange format Not an standard, RFC 976, Januari 1986. offi-cial IETF standard, but in reality a de-facto standard for Usenet News 19] T. Berners-Lee, R. Headering, H. Frystyk: IETF draft Hypertext Transfer Protocol -- HTTP/1.0, draft-ietf-http-v10-spec-04.txt.  G. Vaudreuil: Voice Profile for Internet Experimental Mail, RFC 1911, February 1996.  H. Spencer: News Article Format and Not even an Transmission, June 1994, RFC, but still FTP://zoo.toronto.edu/pub/news.ps.Z widely used and FTP://zoo.toronto.edu/pub/news.txt.Z partly almost a de-facto This document is often referenced under standard for the name "son-of-RFC1036". Usenet News 22] J. Palme: Common Internet Message Headers. Informational draft-ietf-mailext-mail-attributes-07.txt. January 1997. 9. Author's address Jacob Palme Phone: +46-8-16 16 67 Stockholm University/KTH Fax: +46-8-783 08 29 Electrum 230 E-mail: firstname.lastname@example.org S-164 40 Kista, Sweden 10. Appendix: Proposed initial content of the IETF header name registry Note: The descriptions in the leftmost columns are intentionally very brief and may therefore not give a complete and fully accurate description of the header. Hint on usage Header name Source Status -------------- ----------- ------------------ ---------------- Special Usenet Also-Contro son-of-RFC1036 Non-standard, News actions. l: . only in Usenet News, not in e-mail. Controls X.400 Alternate-R RFC 1327. X.400. forwarding. ecipient: Inserted by Apparently- RFC 1211 and . Non-standard, Sendmail. To: discouraged. Mark of Approved: RFC 1036: 2.2.11. Only in Usenet approval by News, not in moderator. e-mail. Specially Article-Nam son-of-RFC1036 Non-standard. important es: . articles. Revised Article-Upd son-of-RFC1036 Non-standard. version ates: . article. Has been Auto-Forwar RFC 1327. X.400. automatically ded: forwarded. Recipients not bcc: RFC 822: 4.5.3, IETF standard. to be RFC 1123: disclosed. 5.2.15-16, 5.3.7. Secondary cc: RFC 822: 4.5.2, IETF standard. recipients. RFC 1123. 5.2.15-16, 5.3.7. Comments on a Comments: RFC 822: 4.7.2. IETF standard. message. Base for Content-Bas In forthcoming Soon IETF resolving e: MHTML standard. proposed relative URLs. standard. Conversion Content-Con See . Non-standard. control. version: Description of Content-Des RFC 1521: 6.2. IETF draft body part. cription: standard. Inline or Content-Dis RFC 1806. IETF attachment. position: experimental standard. Unique ID of Content-ID: RFC 1521: 6.1. IETF draft one body part. standard. Text string Content-Ide RFC 1327. X.400. identifier. ntifier: Language(s) of Content-Lan RFC 1766. IETF proposed body part. guage: standard. Size in bytes. Content-Len See . Non-standard, gth: discouraged. URI for body Content-Loc In forthcoming Soon IETF part. ation: MHTML proposed proposed standard. standard. Checksum of Content-MD5 RFC 1864. IETF proposed content. : standard. Return content Content-Ret RFC 1327. X.400. in X.400 urn: delivery notifications? . From the SGML Content-SGM Other standard. entity L-Entity: declaration. Coding method. Content-Tra RFC 1521: 5. IETF draft nsfer-Encod standard. ing: Format of Content-Typ RFC 1049, IETF draft content. e: RFC 1123: 5.2.13, standard. RFC 1521: 4. RFC 1766: 4.1 Special Usenet Control: RFC 1036: 2.1.6. Only in Usenet News actions News, not in only. e-mail. Body may not Conversion- RFC 1327. X.400. be converted With-Loss: with loss. Body may not Conversion: RFC 1327. X.400. be converted. When message Date: RFC 822: 5.1, IETF standard. was created. RFC 1123: 5.2.14 RFC 1036: 2.1.2. When message Delivery-Da RFC 1327. X.400. was delivered. te: X.400 Discarded-X RFC 1327. X.400. extensions not 400-IPMS-Ex mapped. tensions: X.400 Discarded-X RFC 1327. X.400. extensions not 400-MTS-Ext mapped. ensions: Tell recipient Disclose-Re RFC 1327. X.400. about other cipients: recipients. Limitation of Distributio RFC 1036: 2.2.7. Usenet news distribution n: only, not in area. e-mail. Trace of lists DL-Expansio RFC 1327. X.400. passed. n-History-I ndication: Several Encoding: RFC 1154, IETF different RFC 1505, experimental incompatible standard. uses. Where to send Errors-To: See . Non-standard, notifications. discouraged. Expiration Expires: RFC 1036: 2.2.4. Usenet news date. only, not in e-mail. Expiration Expiry-Date RFC 1327. X.400. date. : Fax number of Fax: Non-standard. the originator. File where Fcc: See . Non-standard. message is stored. Where to Followup-To RFC 1036: 2.2.3. Usenet news discuss item : only, not in further. e-mail. Variant of For-Comment See . Non-standard. "To:" : Variant of For-Handlin See . Non-standard. "To: g: (1) Message From See . Discouraged in separator in transport of files. e-mail. (2) Usenet From RFC 976: 2.4 Usenet news news delivery or only, not in path. >From e-mail. Author From: RFC 822: 4.4.1, IETF standard. RFC 1123: 5.2.15-16, 5.3.7, RFC 1036 2.1.1 Delivery Generate-De RFC 1327. X.400. report livery-Repo generation rt: control. Values: High, Importance: RFC 1327 and IETF normal or low. RFC 1911. experimental standard. Message being In-Reply-To RFC 822: 4.6.2. replied to. : Body parts are Incomplete- RFC 1327. X.400. missing. Copy: Search keys Keywords: RFC 822: 4.7.1 for retrieval. RFC 1036: 2.2.9. Language of Language: RFC 1327, X.400. message. Size of the Lines: RFC 1036: 2.2.12. Usenet news message. only, not in e-mail. Generating Mail-System Non-standard, client -Version: discouraged. software. Generating Mailer: Non-standard, client discouraged. software. Unique ID of Message-ID: RFC 822: 4.6.1 IETF standard. this message. RFC 1036: 2.1.5. Report or Message-Typ RFC 1327. X.400. message. e: Version of MIME-Versio RFC 1521: 3. IETF draft MIME. n: standard. Newsgroups Newsgroups: RFC 1036: 2.1.3, Usenet news getting this see also. only, article. discouraged in e-mail. Previous Obsoletes: RFC 1327. X.400. message being replaced. Sender Organisatio Discouraged. organzation. n: Sender Organizatio RFC 1036: 2.2.8. Usenet news organization. n: only, discouraged in e-mail. Body part Original-En RFC 1327. X.400. types in coded-Infor message. mation-Type s: Generating Originating Non-standard, client -Client: discouraged. software. List of MTAs Path: RFC 1036: 2.2.6. Usenet news passed. only, not in e-mail. Phone number Phone: . Non-standard of the originator. Priority, Precedence: See . Non-standard, might controversial, influence discouraged. speed. Non-delivery Prevent-Non RFC 1327. X.400. report Delivery-Re control. port: Priority, Priority: RFC 1327. X.400. might influence speed. Trace of MTAs Received: RFC 822: 4.3.2, IETF standard. passed. RFC 1123: 5.2.8. Reference to References: RFC 822: 4.6.3 IETF standard. other RFC 1036: 2.1.5. messages. Latest reply Reply-By: RFC 1327. X.400. time. Where to send Reply-To: RFC 822: 4.4.3, IETF standard replies. RFC 1036: 2.2.1 but see also . controversial. Information Resent-Repl RFC 822: C.3.3. IETF standard. about manual y-To:, forwarding. Resent-From:, Resent-Sender:, Resent-From;, Resent-Date;, Resent-To:, Resent-cc:, Resent-bcc:, Resent-Mess age-ID: Envelope info Return-Path RFC 821, IETF standard. at final : RFC 1123: 5.2.13. delivery. Where to send Return-Rece See . Non-standard, notifications. ipt-To: discouraged. Related See-Also: Son-of-RFC1036 Non-standard. articles. . Sender if not Sender: RFC 822: 4.4.2, IETF standard. same as in RFC 1123: from header. 5.2.15-16, 5.3.7. Disclosure Sensitivity RFC 1327 and IETF secrecy. : RFC 1911. experimental standard. Whether Status: See . Non-standard, message has should never been appear in mail delivered. in transit. Title, Subject: RFC 822: 4.7.1 IETF standard. heading, RFC 1036: 2.1.4. subject. Short version Summary: RFC 1036: 2.2.10. Usenet news of long only, message. discouraged. Replaces Supersedes: Son-of-RFC1036 Non-standard. previous . article. Fax number of Telefax: Non-standard. the originator. Primary To: RFC 822: 4.5.1, IETF standard. recipients. RFC 1123: 5.2.15-16, 5.3.7. Generating X-Mailer: Non-standard. client software. Generating X-Newsreade Non-standard. client r software. Control of X400-Conten Non-standard. content-return t-Return: . Other Xref: RFC 1036: 2.2.13. Usenet news newsgroups only, not in getting the e-mail. same article.