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Network Working Group G. Klyne
Request for Comments: 4021 University of Oxford
Category: Standards Track J. Palme
Stockholm University/KT
March 2005
Registration of Mail and MIME Header Fields
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document defines the initial IANA registration for permanent
mail and MIME message header fields, per RFC 3864.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Structure of This Document . . . . . . . . . . . . . . . 3
1.2. Document Terminology and Conventions . . . . . . . . . . 4
2. Registration Templates . . . . . . . . . . . . . . . . . . . . 4
2.1. Permanent Mail Header Field Registrations . . . . . . . 4
2.1.1. Header Field: Date . . . . . . . . . . . . . . . 6
2.1.2. Header Field: From . . . . . . . . . . . . . . . 7
2.1.3. Header Field: Sender . . . . . . . . . . . . . . 7
2.1.4. Header Field: Reply-To . . . . . . . . . . . . . 8
2.1.5. Header Field: To . . . . . . . . . . . . . . . . 8
2.1.6. Header Field: Cc . . . . . . . . . . . . . . . . 9
2.1.7. Header Field: Bcc . . . . . . . . . . . . . . . 9
2.1.8. Header Field: Message-ID . . . . . . . . . . . . 10
2.1.9. Header Field: In-Reply-To . . . . . . . . . . . 10
2.1.10. Header Field: References . . . . . . . . . . . . 11
2.1.11. Header Field: Subject . . . . . . . . . . . . . 11
2.1.12. Header Field: Comments . . . . . . . . . . . . . 12
2.1.13. Header Field: Keywords . . . . . . . . . . . . . 12
2.1.14. Header Field: Resent-Date . . . . . . . . . . . 13
2.1.15. Header Field: Resent-From . . . . . . . . . . . 13
2.1.16. Header Field: Resent-Sender . . . . . . . . . . 14
G. Klyne, et al. Standards Track [Page 1]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.17. Header Field: Resent-To . . . . . . . . . . . . 14 2.1.18. Header Field: Resent-Cc . . . . . . . . . . . . 15 2.1.19. Header Field: Resent-Bcc . . . . . . . . . . . . 15 2.1.20. Header Field: Resent-Reply-To . . . . . . . . . 16 2.1.21. Header Field: Resent-Message-ID . . . . . . . . 16 2.1.22. Header Field: Return-Path . . . . . . . . . . . 17 2.1.23. Header Field: Received . . . . . . . . . . . . . 17 2.1.24. Header Field: Encrypted . . . . . . . . . . . . 18 2.1.25. Header Field: Disposition-Notification-To . . . 18 2.1.26. Header Field: Disposition-Notification-Options . 19 2.1.27. Header Field: Accept-Language . . . . . . . . . 19 2.1.28. Header Field: Original-Message-ID . . . . . . . 20 2.1.29. Header Field: PICS-Label . . . . . . . . . . . . 20 2.1.30. Header Field: Encoding . . . . . . . . . . . . . 21 2.1.31. Header Field: List-Archive . . . . . . . . . . . 21 2.1.32. Header Field: List-Help . . . . . . . . . . . . 22 2.1.33. Header Field: List-ID . . . . . . . . . . . . . 22 2.1.34. Header Field: List-Owner . . . . . . . . . . . . 23 2.1.35. Header Field: List-Post . . . . . . . . . . . . 23 2.1.36. Header Field: List-Subscribe . . . . . . . . . . 24 2.1.37. Header Field: List-Unsubscribe . . . . . . . . . 24 2.1.38. Header Field: Message-Context . . . . . . . . . 25 2.1.39. Header Field: DL-Expansion-History . . . . . . . 25 2.1.40. Header Field: Alternate-Recipient . . . . . . . 26 2.1.41. Header Field: Original-Encoded-Information-Types 26 2.1.42. Header Field: Content-Return . . . . . . . . . . 27 2.1.43. Header Field: Generate-Delivery-Report . . . . . 27 2.1.44. Header Field: Prevent-NonDelivery-Report . . . . 28 2.1.45. Header Field: Obsoletes . . . . . . . . . . . . 28 2.1.46. Header Field: Supersedes . . . . . . . . . . . . 29 2.1.47. Header Field: Content-Identifier . . . . . . . . 29 2.1.48. Header Field: Delivery-Date . . . . . . . . . . 30 2.1.49. Header Field: Expiry-Date . . . . . . . . . . . 30 2.1.50. Header Field: Expires . . . . . . . . . . . . . 31 2.1.51. Header Field: Reply-By . . . . . . . . . . . . . 31 2.1.52. Header Field: Importance . . . . . . . . . . . . 32 2.1.53. Header Field: Incomplete-Copy . . . . . . . . . 32 2.1.54. Header Field: Priority . . . . . . . . . . . . . 33 2.1.55. Header Field: Sensitivity . . . . . . . . . . . 33 2.1.56. Header Field: Language . . . . . . . . . . . . . 34 2.1.57. Header Field: Conversion . . . . . . . . . . . . 34 2.1.58. Header Field: Conversion-With-Loss . . . . . . . 35 2.1.59. Header Field: Message-Type . . . . . . . . . . . 35 2.1.60. Header Field: Autosubmitted . . . . . . . . . . 36 2.1.61. Header Field: Autoforwarded . . . . . . . . . . 36 2.1.62. Header Field: Discarded-X400-IPMS-Extensions . . 37 2.1.63. Header Field: Discarded-X400-MTS-Extensions . . 37 2.1.64. Header Field: Disclose-Recipients . . . . . . . 38 G. Klyne, et al. Standards Track [Page 2]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.65. Header Field: Deferred-Delivery . . . . . . . . 38 2.1.66. Header Field: Latest-Delivery-Time . . . . . . . 39 2.1.67. Header Field: Originator-Return-Address . . . . 39 2.1.68. Header Field: X400-Content-Identifier . . . . . 40 2.1.69. Header Field: X400-Content-Return . . . . . . . 40 2.1.70. Header Field: X400-Content-Type . . . . . . . . 41 2.1.71. Header Field: X400-MTS-Identifier . . . . . . . 41 2.1.72. Header Field: X400-Originator . . . . . . . . . 42 2.1.73. Header Field: X400-Received . . . . . . . . . . 42 2.1.74. Header Field: X400-Recipients . . . . . . . . . 43 2.1.75. Header Field: X400-Trace . . . . . . . . . . . . 43 2.2. Permanent MIME Header Field Registrations . . . . . . . 44 2.2.1. Header Field: MIME-Version . . . . . . . . . . . 44 2.2.2. Header Field: Content-ID . . . . . . . . . . . . 45 2.2.3. Header Field: Content-Description . . . . . . . 45 2.2.4. Header Field: Content-Transfer-Encoding . . . . 46 2.2.5. Header Field: Content-Type . . . . . . . . . . . 46 2.2.6. Header Field: Content-Base . . . . . . . . . . . 47 2.2.7. Header Field: Content-Location . . . . . . . . . 47 2.2.8. Header Field: Content-features . . . . . . . . . 48 2.2.9. Header Field: Content-Disposition . . . . . . . 48 2.2.10. Header Field: Content-Language . . . . . . . . . 49 2.2.11. Header Field: Content-Alternative . . . . . . . 49 2.2.12. Header Field: Content-MD5 . . . . . . . . . . . 50 2.2.13. Header Field: Content-Duration . . . . . . . . . 50 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 50 4. Security Considerations . . . . . . . . . . . . . . . . . . . 51 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 51 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 51 6.1. Normative References . . . . . . . . . . . . . . . . . . 51 6.2. Informative References . . . . . . . . . . . . . . . . . 53 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 53 Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 54 1. Introduction This document defines IANA registration for a number of mail message and MIME header fields, per registration procedures for message header fields [1]. The main body of this document is automatically generated from RDF/N3 data. Some experimental HTML registry pages have been prepared from the same data and can be found at [27]. 1.1. Structure of This Document Section 2.1 contains the templates for initial registration of mail message header fields. G. Klyne, et al. Standards Track [Page 3]
RFC 4021 Mail and MIME Header Fields March 2005 Section 2.2 contains templates for initial registration of MIME header fields. 1.2. Document Terminology and Conventions 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 BCP 14, RFC 2119 [9]. 2. Registration Templates Header field registry entries are summarized in tabular form for convenience of reference and presented in full in the following sections. 2.1. Permanent Mail Header Field Registrations Header name Protocol ----------- -------- Date Mail Message date and time From Mail Mailbox of message author Sender Mail Mailbox of message sender Reply-To Mail Mailbox for replies to message To Mail Primary recipient mailbox Cc Mail Carbon-copy recipient mailbox Bcc Mail Blind-carbon-copy recipient mailbox Message-ID Mail Message identifier In-Reply-To Mail Identify replied-to message(s) References Mail Related message identifier(s) Subject Mail Topic of message Comments Mail Additional comments about the message Keywords Mail Message key words and/or phrases Resent-Date Mail Date and time message is resent Resent-From Mail Mailbox of person for whom message is resent Resent-Sender Mail Mailbox of person who actually resends the message Resent-To Mail Mailbox to which message is resent Resent-Cc Mail Mailbox(es) to which message is cc'ed on resend Resent-Bcc Mail Mailbox(es) to which message is bcc'ed on resend Resent-Reply-To Mail Resent reply-to Resent-Message-ID Mail Message identifier for resent message G. Klyne, et al. Standards Track [Page 4]
RFC 4021 Mail and MIME Header Fields March 2005 Return-Path Mail Message return path Received Mail Mail transfer trace information Encrypted Mail Message encryption information Disposition-Notification-To Mail Mailbox for sending disposition notification Disposition-Notification-Options Mail Disposition notification options Accept-Language Mail Language(s) for auto-responses Original-Message-ID Mail Original message identifier PICS-Label Mail PICS rating label Encoding Mail Message encoding and other information List-Archive Mail URL of mailing list archive List-Help Mail URL for mailing list information List-ID Mail Mailing list identifier List-Owner Mail URL for mailing list owner's mailbox List-Post Mail URL for mailing list posting List-Subscribe Mail URL for mailing list subscription List-Unsubscribe Mail URL for mailing list unsubscription Message-Context Mail Type or context of message DL-Expansion-History Mail Trace of distribution lists passed Alternate-Recipient Mail Controls forwarding to alternate recipients Original-Encoded-Information-Types Mail Body part types in message Content-Return Mail Return content on non-delivery? Generate-Delivery-Report Mail Request delivery report generation Prevent-NonDelivery-Report Mail Non-delivery report required? Obsoletes Mail Reference message to be replaced Supersedes Mail Reference message to be replaced Content-Identifier Mail Message content identifier Delivery-Date Mail Message delivery time Expiry-Date Mail Message expiry time Expires Mail Message expiry time Reply-By Mail Time by which a reply is requested Importance Mail Message importance Incomplete-Copy Mail Body parts are missing Priority Mail Message priority Sensitivity Mail Message content sensitivity Language Mail X.400 message content language Conversion Mail Conversion allowed? G. Klyne, et al. Standards Track [Page 5]
RFC 4021 Mail and MIME Header Fields March 2005 Conversion-With-Loss Mail Lossy conversion allowed? Message-Type Mail Message type: delivery report? Autosubmitted Mail Automatically submitted indicator Autoforwarded Mail Automatically forwarded indicator Discarded-X400-IPMS-Extensions Mail X.400 IPM extensions discarded Discarded-X400-MTS-Extensions Mail X.400 MTS extensions discarded Disclose-Recipients Mail Disclose names of other recipients? Deferred-Delivery Mail Deferred delivery information Latest-Delivery-Time Mail Latest delivery time requested Originator-Return-Address Mail Originator return address X400-Content-Identifier Mail Message content identifier X400-Content-Return Mail Return content on non-delivery? X400-Content-Type Mail X400 content type X400-MTS-Identifier Mail X400 MTS-Identifier X400-Originator Mail X400 Originator X400-Received Mail X400 Received X400-Recipients Mail X400 Recipients X400-Trace Mail X400 Trace 2.1.1. Header Field: Date Description: Message date and time Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.1) Related information: Specifies the date and time at which the creator of the message indicated that the message was complete and ready to enter the mail delivery system. Defined as standard by RFC 822. G. Klyne, et al. Standards Track [Page 6]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.2. Header Field: From Description: Mailbox of message author Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.2) Related information: Specifies the author(s) of the message; that is, the mailbox(es) of the person(s) or system(s) responsible for the writing of the message. Defined as standard by RFC 822. 2.1.3. Header Field: Sender Description: Mailbox of message sender Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.2) Related information: Specifies the mailbox of the agent responsible for the actual transmission of the message. Defined as standard by RFC 822. G. Klyne, et al. Standards Track [Page 7]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.4. Header Field: Reply-To Description: Mailbox for replies to message Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.2) Related information: When the "Reply-To:" field is present, it indicates the mailbox(es) to which the author of the message suggests that replies be sent. Defined as standard by RFC 822. 2.1.5. Header Field: To Description: Primary recipient mailbox Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.3) Related information: Contains the address(es) of the primary recipient(s) of the message. Defined as standard by RFC 822. G. Klyne, et al. Standards Track [Page 8]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.6. Header Field: Cc Description: Carbon-copy recipient mailbox Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.3) Related information: Contains the addresses of others who are to receive the message, though the content of the message may not be directed at them. Defined as standard by RFC 822. 2.1.7. Header Field: Bcc Description: Blind-carbon-copy recipient mailbox Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.3) Related information: Contains addresses of recipients of the message whose addresses are not to be revealed to other recipients of the message. Defined as standard by RFC 822. G. Klyne, et al. Standards Track [Page 9]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.8. Header Field: Message-ID Description: Message identifier Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.4) Related information: Contains a single unique message identifier that refers to a particular version of a particular message. If the message is resent without changes, the original Message-ID is retained. Defined as standard by RFC 822. 2.1.9. Header Field: In-Reply-To Description: Identify replied-to message(s) Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.4) Related information: The message identifier(s) of the original message(s) to which the current message is a reply. Defined as standard by RFC 822. G. Klyne, et al. Standards Track [Page 10]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.10. Header Field: References Description: Related message identifier(s) Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.4) Related information: The message identifier(s) of other message(s) to which the current message may be related. In RFC 2822, the definition was changed to say that this header field contains a list of all Message-IDs of messages in the preceding reply chain. Defined as standard by RFC 822. 2.1.11. Header Field: Subject Description: Topic of message Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.5) Related information: Contains a short string identifying the topic of the message. Defined as standard by RFC 822. G. Klyne, et al. Standards Track [Page 11]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.12. Header Field: Comments Description: Additional comments about the message Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.5) Related information: Contains any additional comments on the text of the body of the message. Warning: Some mailers will not show this field to recipients. Defined as standard by RFC 822. 2.1.13. Header Field: Keywords Description: Message key words and/or phrases Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.5) Related information: Contains a comma-separated list of important words and phrases that might be useful for the recipient. Defined as standard by RFC 822. G. Klyne, et al. Standards Track [Page 12]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.14. Header Field: Resent-Date Description: Date and time message is resent Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.6) Related information: Contains the date and time that a message is reintroduced into the message transfer system. Defined as standard by RFC 822. 2.1.15. Header Field: Resent-From Description: Mailbox of person for whom message is resent Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.6) Related information: Contains the mailbox of the agent who has reintroduced the message into the message transfer system, or on whose behalf the message has been resent. Defined as standard by RFC 822. G. Klyne, et al. Standards Track [Page 13]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.16. Header Field: Resent-Sender Description: Mailbox of person who actually resends the message Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.6) Related information: Contains the mailbox of the agent who has reintroduced the message into the message transfer system, if this is different from the Resent-From value. Defined as standard by RFC 822. 2.1.17. Header Field: Resent-To Description: Mailbox to which message is resent Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.6) Related information: Contains the mailbox(es) to which the message has been resent. Defined as standard by RFC 822. G. Klyne, et al. Standards Track [Page 14]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.18. Header Field: Resent-Cc Description: Mailbox(es) to which message is cc'ed on resend Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.6) Related information: Contains the mailbox(es) to which message is cc'ed on resend. Defined as standard by RFC 822. 2.1.19. Header Field: Resent-Bcc Description: Mailbox(es) to which message is bcc'ed on resend Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.6) Related information: Contains the mailbox(es) to which message is bcc'ed on resend. Defined as standard by RFC 822. G. Klyne, et al. Standards Track [Page 15]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.20. Header Field: Resent-Reply-To Description: Resent reply-to Applicable protocol: Mail [18] Status: obsolete Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] Related information: Resent Reply-to. Defined by RFC 822, obsoleted by RFC 2822. 2.1.21. Header Field: Resent-Message-ID Description: Message identifier for resent message Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.6) Related information: Contains a message identifier for a resent message. Defined as standard by RFC 822. G. Klyne, et al. Standards Track [Page 16]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.22. Header Field: Return-Path Description: Message return path Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.7) Related information: Return path for message response diagnostics. See also RFC 2821 [17]. Defined as standard by RFC 822. 2.1.23. Header Field: Received Description: Mail transfer trace information Applicable protocol: Mail [18] Status: standard Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2822 [18] (section 3.6.7) Related information: Contains information about receipt of the current message by a mail transfer agent on the transfer path. See also RFC 2821 [17]. Defined as standard by RFC 822. G. Klyne, et al. Standards Track [Page 17]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.24. Header Field: Encrypted Description: Message encryption information Applicable protocol: Mail [18] Status: obsolete Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 822 [2] Related information: Defined by RFC 822, but was found to be inadequately specified, was not widely implemented, and was removed in RFC 2822. Current practice is to use separate encryption, such as S/MIME or OpenPGP, possibly in conjunction with RFC 1847 MIME security multiparts. 2.1.25. Header Field: Disposition-Notification-To Description: Mailbox for sending disposition notification Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2298 [12] Related information: Indicates that the sender wants a disposition notification when this message is received (read, processed, etc.) by its recipients. G. Klyne, et al. Standards Track [Page 18]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.26. Header Field: Disposition-Notification-Options Description: Disposition notification options Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2298 [12] Related information: For optional modifiers on disposition notification requests. 2.1.27. Header Field: Accept-Language Description: Language(s) for auto-responses Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 3282 [21] Related information: Indicates a language that the message sender requests to be used for responses. Accept-language was not designed for email but has been considered useful as input to the generation of automatic replies. Some problems have been noted concerning its use with email, including but not limited to determination of the email address to which it refers; cost and lack of effective internationalization of email responses; interpretation of language subtags; and determining what character set encoding should be used. G. Klyne, et al. Standards Track [Page 19]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.28. Header Field: Original-Message-ID Description: Original message identifier Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 3297 [22] Related information: Original message identifier used with resend of message with alternative content format; identifies the original message data to which it corresponds. 2.1.29. Header Field: PICS-Label Description: PICS rating label Applicable protocol: Mail [18] Status: standard Author/change controller: W3C (mailto:web-human@w3.org) World Wide Web Consortium Specification document(s): PICS-labels [24] Related information: Ratings label to control selection (filtering) of messages according to the PICS protocol. Specified for general use with RFC 822 message format, with HTTP-specific extensions. G. Klyne, et al. Standards Track [Page 20]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.30. Header Field: Encoding Description: Message encoding and other information Applicable protocol: Mail [18] Status: experimental Author/change controller: Albert K. Costanzo (mailto:AL@AKC.COM) AKC Consulting Inc. Specification document(s): RFC 1505 [4] Related information: Used in several different ways by different mail systems. Some use it for a kind of content-type information, some for encoding and length information, some for a kind of boundary information, and some in other ways. 2.1.31. Header Field: List-Archive Description: URL of mailing list archive Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2369 [13] Related information: Contains the URL to use to browse the archives of the mailing list from which this message was relayed. G. Klyne, et al. Standards Track [Page 21]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.32. Header Field: List-Help Description: URL for mailing list information Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2369 [13] Related information: Contains the URL to use to get information about the mailing list from which this message was relayed. 2.1.33. Header Field: List-ID Description: Mailing list identifier Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2919 [20] Related information: Stores an identification of the mailing list through which this message was distributed. G. Klyne, et al. Standards Track [Page 22]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.34. Header Field: List-Owner Description: URL for mailing list owner's mailbox Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2369 [13] Related information: Contains the URL to send e-mail to the owner of the mailing list from which this message was relayed. 2.1.35. Header Field: List-Post Description: URL for mailing list posting Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2369 [13] Related information: Contains the URL to use to send contributions to the mailing list from which this message was relayed. G. Klyne, et al. Standards Track [Page 23]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.36. Header Field: List-Subscribe Description: URL for mailing list subscription Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2369 [13] Related information: Contains the URL to use to get a subscription to the mailing list from which this message was relayed. 2.1.37. Header Field: List-Unsubscribe Description: URL for mailing list unsubscription Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2369 [13] Related information: Contains the URL to use to unsubscribe the mailing list from which this message was relayed. G. Klyne, et al. Standards Track [Page 24]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.38. Header Field: Message-Context Description: Type or context of message Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 3458 [23] Related information: Provides information about the context and presentation characteristics of a message. Can have the values 'voice- message', 'fax-message', 'pager-message', 'multimedia-message', 'text-message', or 'none'. 2.1.39. Header Field: DL-Expansion-History Description: Trace of distribution lists passed Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Trace of distribution lists passed. (MIXER X.400 mapping; not for general use.) G. Klyne, et al. Standards Track [Page 25]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.40. Header Field: Alternate-Recipient Description: Controls forwarding to alternate recipients Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Controls whether this message may be forwarded to an alternate recipient, such as a postmaster, if delivery to the intended recipient is not possible. Default: Allowed. RFC 2156 (MIXER), not for general use. 2.1.41. Header Field: Original-Encoded-Information-Types Description: Body part types in message Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Which body part types occur in this message. RFC 2156 (MIXER); not for general use. G. Klyne, et al. Standards Track [Page 26]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.42. Header Field: Content-Return Description: Return content on non-delivery? Applicable protocol: Mail [18] Status: obsolete Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 1327 [3] Related information: Indicates whether the content of a message is to be returned with non-delivery notifications. Introduced by RFC 1327 and subsequently changed by RFC 2156 to avoid confusion with MIME defined fields. 2.1.43. Header Field: Generate-Delivery-Report Description: Request delivery report generation Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Indicates whether a delivery report is wanted at successful delivery. Default is not to generate such a report. RFC 2156 (MIXER); not for general use. G. Klyne, et al. Standards Track [Page 27]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.44. Header Field: Prevent-NonDelivery-Report Description: Non-delivery report required? Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Indicates whether a non-delivery report is wanted on delivery error. Default is to generate such a report. RFC 2156 (MIXER); not for general use. 2.1.45. Header Field: Obsoletes Description: Reference message to be replaced Applicable protocol: Mail [18] Status: obsolete Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 1327 [3] Related information: Reference to a previous message being corrected and replaced. Compare to 'Supersedes:',f used in Usenet News. Introduced by RFC 1327 and subsequently renamed by RFC 2156 to 'Supersedes'. G. Klyne, et al. Standards Track [Page 28]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.46. Header Field: Supersedes Description: Reference message to be replaced Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Reference to a previous message being corrected and replaced. Renamed version of obsolete 'Obsoletes' header field. RFC 2156 (MIXER); not for general use. 2.1.47. Header Field: Content-Identifier Description: Message content identifier Applicable protocol: Mail [18] Status: obsolete Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 1327 [3] Related information: A text string that identifies the content of a message. Introduced by RFC 1327 and subsequently changed by RFC 2156 to avoid confusion with MIME defined fields. Gateways that reverse map may support the old field. G. Klyne, et al. Standards Track [Page 29]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.48. Header Field: Delivery-Date Description: Message delivery time Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: The time when a message was delivered to its recipient. RFC 2156 (MIXER); not for general use. 2.1.49. Header Field: Expiry-Date Description: Message expiry time Applicable protocol: Mail [18] Status: obsolete Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 1327 [3] Related information: Time at which a message loses its validity. Introduced by RFC 1327 and subsequently changed by RFC 2156 to 'Expires:'. G. Klyne, et al. Standards Track [Page 30]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.50. Header Field: Expires Description: Message expiry time Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Time at which a message loses its validity. Renamed version of obsolete Expiry-Date header field. RFC 2156 (MIXER), not for general use. 2.1.51. Header Field: Reply-By Description: Time by which a reply is requested Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Latest time by which a reply is requested (not demanded). RFC 2156 (MIXER); not for general use. G. Klyne, et al. Standards Track [Page 31]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.52. Header Field: Importance Description: Message importance Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: A hint from the originator to the recipients about how important a message is. Values: High, normal, or low. Not used to control transmission speed. Proposed for use with RFC 2156 (MIXER) [10] and RFC 3801 (VPIM) [14]. 2.1.53. Header Field: Incomplete-Copy Description: Body parts are missing Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Body parts are missing. RFC 2156 (MIXER); not for general use. G. Klyne, et al. Standards Track [Page 32]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.54. Header Field: Priority Description: Message priority Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Can be 'normal', 'urgent', or 'non-urgent' and can influence transmission speed and delivery. RFC 2156 (MIXER); not for general use. 2.1.55. Header Field: Sensitivity Description: Message content sensitivity Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: How sensitive it is to disclose this message to people other than the specified recipients. Values: Personal, private, and company confidential. The absence of this header field in messages gatewayed from X.400 indicates that the message is not sensitive. Proposed for use with RFC 2156 (MIXER) [10] and RFC 3801 (VPIM) [14]. G. Klyne, et al. Standards Track [Page 33]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.56. Header Field: Language Description: X.400 message content language Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Can include a code for the natural language used in a message; e.g., 'en' for English. See also 'Content-Language'. RFC 2156 (MIXER); not for general use. 2.1.57. Header Field: Conversion Description: Conversion allowed? Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: The body of this message may not be converted from one character set to another. Values: prohibited and allowed. RFC 2156 (MIXER); not for general use. G. Klyne, et al. Standards Track [Page 34]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.58. Header Field: Conversion-With-Loss Description: Lossy conversion allowed? Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: The body of this message may not be converted from one character set to another if information will be lost. Values: prohibited and allowed. RFC 2156 (MIXER); not for general use. 2.1.59. Header Field: Message-Type Description: Message type: delivery report? Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Only used with the value 'Delivery Report' to indicate that this is a delivery report gatewayed from X.400. RFC 2156 (MIXER); not for general use. G. Klyne, et al. Standards Track [Page 35]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.60. Header Field: Autosubmitted Description: Automatically submitted indicator Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Has been automatically submitted. RFC 2156 (MIXER); not for general use. 2.1.61. Header Field: Autoforwarded Description: Automatically forwarded indicator Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Has been automatically forwarded. RFC 2156 (MIXER), not for general use. G. Klyne, et al. Standards Track [Page 36]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.62. Header Field: Discarded-X400-IPMS-Extensions Description: X.400 IPM extensions discarded Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Can be used in Internet mail to indicate X.400 IPM extensions that could not be mapped to Internet mail format. RFC 2156 (MIXER); not for general use. 2.1.63. Header Field: Discarded-X400-MTS-Extensions Description: X.400 MTS extensions discarded Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Can be used in Internet mail to indicate X.400 MTS extensions that could not be mapped to Internet mail format. RFC 2156 (MIXER); not for general use. G. Klyne, et al. Standards Track [Page 37]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.64. Header Field: Disclose-Recipients Description: Disclose names of other recipients? Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Tells whether recipients are to be told the names of other recipients of the same message. This is primarily an X.400 facility. In X.400, this is an envelope attribute and refers to disclosure of the envelope recipient list. Disclosure of other recipients is done in Internet mail via the To:, cc:, and bcc: header fields. Not for general use. 2.1.65. Header Field: Deferred-Delivery Description: Deferred delivery information Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Provides information about deferred delivery service to the recipient. RFC 2156 (MIXER); not for general use. G. Klyne, et al. Standards Track [Page 38]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.66. Header Field: Latest-Delivery-Time Description: Latest delivery time requested Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Provides the recipient with information about requested delivery but will not be acted on by the SMTP infrastructure. RFC 2156 (MIXER); not for general use. 2.1.67. Header Field: Originator-Return-Address Description: Originator return address Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Originator return address. RFC 2156 (MIXER); not for general use. G. Klyne, et al. Standards Track [Page 39]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.68. Header Field: X400-Content-Identifier Description: Message content identifier Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: A text string that identifies the content of a message. Renamed version of obsolete Content-Identifier field. RFC 2156 (MIXER); not for general use. 2.1.69. Header Field: X400-Content-Return Description: Return content on non-delivery? Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: Indicates whether the content of a message is to be returned with non-delivery notifications. Renamed version of obsolete Content- Return field. RFC 2156 (MIXER); not for general use. G. Klyne, et al. Standards Track [Page 40]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.70. Header Field: X400-Content-Type Description: X400 content type Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: X400 content type. RFC 2156 (MIXER); not for general use. 2.1.71. Header Field: X400-MTS-Identifier Description: X400 MTS-Identifier Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: X400 MTS-Identifier. RFC 2156 (MIXER); not for general use. G. Klyne, et al. Standards Track [Page 41]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.72. Header Field: X400-Originator Description: X400 Originator Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: X400 Originator. RFC 2156 (MIXER); not for general use. 2.1.73. Header Field: X400-Received Description: X400 Received Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: X400 Received. RFC 2156 (MIXER); not for general use. G. Klyne, et al. Standards Track [Page 42]
RFC 4021 Mail and MIME Header Fields March 2005 2.1.74. Header Field: X400-Recipients Description: X400 Recipients Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: X400 Recipients. RFC 2156 (MIXER); not for general use. 2.1.75. Header Field: X400-Trace Description: X400 Trace Applicable protocol: Mail [18] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2156 [10] Related information: X400 Trace. RFC 2156 (MIXER), not for general use. G. Klyne, et al. Standards Track [Page 43]
RFC 4021 Mail and MIME Header Fields March 2005 2.2. Permanent MIME Header Field Registrations Header name Protocol ----------- -------- MIME-Version MIME MIME version number Content-ID MIME Identify content body part Content-Description MIME Description of message body part Content-Transfer-Encoding MIME Content transfer encoding applied Content-Type MIME MIME content type Content-Base MIME Base to be used for resolving relative URIs within this content part Content-Location MIME URI for retrieving a body part Content-features MIME Indicates content features of a MIME body part Content-Disposition MIME Intended content disposition and file name Content-Language MIME Language of message content Content-Alternative MIME Alternative content available Content-MD5 MIME MD5 checksum of content Content-Duration MIME Time duration of content 2.2.1. Header Field: MIME-Version Description: MIME version number Applicable protocol: MIME [7] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2045 [7] (section 4) Related information: An indicator that this message is formatted according to the MIME standard, and an indication of which version of MIME is used. G. Klyne, et al. Standards Track [Page 44]
RFC 4021 Mail and MIME Header Fields March 2005 2.2.2. Header Field: Content-ID Description: Identify content body part Applicable protocol: MIME [7] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2045 [7] (section 7) Related information: Specifies a Unique ID for one MIME body part of the content of a message. 2.2.3. Header Field: Content-Description Description: Description of message body part Applicable protocol: MIME [7] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2045 [7] (section 8) Related information: Description of a particular body part of a message; for example, a caption for an image body part. G. Klyne, et al. Standards Track [Page 45]
RFC 4021 Mail and MIME Header Fields March 2005 2.2.4. Header Field: Content-Transfer-Encoding Description: Content transfer encoding applied Applicable protocol: MIME [7] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2045 [7] (section 6) Related information: Coding method used in a MIME message body part. 2.2.5. Header Field: Content-Type Description: MIME content type Applicable protocol: MIME [7] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2045 [7] (section 5) Related information: Format of content (character set, etc.) Note that the values for this header field are defined in different ways in RFC 1049 and in MIME (RFC 2045). The 'MIME-version' header field will show whether Content-Type is to be interpreted according to RFC 1049 or according to MIME. The MIME definition should be used in generating mail. RFC 1049 has 'historic' status. RFC 1766 [5] defines a parameter 'difference' to this header field. Various other Content-Type define various additional parameters. For example, the parameter 'charset' is mandatory for all textual Content-Types. See also RFC 1049, RFC 1123: 5.2.13, and RFC 1766: 4.1. G. Klyne, et al. Standards Track [Page 46]
RFC 4021 Mail and MIME Header Fields March 2005 2.2.6. Header Field: Content-Base Description: Base to be used for resolving relative URIs within this content part. Applicable protocol: MIME [7] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2110 [8] Related information: Base to be used for resolving relative URIs within this content part. See also Content-Location. This header was included in the first version of MHTML and HTTP 1.1 but removed in the second version (RFC 2557). 2.2.7. Header Field: Content-Location Description: URI for retrieving a body part Applicable protocol: MIME [7] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2557 [16] Related information: URI using which the content of this body-part part was retrieved, might be retrievable, or which otherwise gives a globally unique identification of the content. G. Klyne, et al. Standards Track [Page 47]
RFC 4021 Mail and MIME Header Fields March 2005 2.2.8. Header Field: Content-features Description: Indicates content features of a MIME body part Applicable protocol: MIME [7] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2912 [19] (section 3) Related information: The 'Content-features:' header can be used to annotate a MIME body part with a media feature expression, to indicate features of the body part content. See also RFC 2533, RFC 2506, and RFC 2045. 2.2.9. Header Field: Content-Disposition Description: Intended content disposition and file name Applicable protocol: MIME [7] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2183 [11] Related information: Indicates whether a MIME body part is to be shown inline or is an attachment; can also indicate a suggested filename for use when saving an attachment to a file. G. Klyne, et al. Standards Track [Page 48]
RFC 4021 Mail and MIME Header Fields March 2005 2.2.10. Header Field: Content-Language Description: Language of message content Applicable protocol: MIME [7] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 3282 [21] Related information: Can include a code for the natural language used in a message; e.g., 'en' for English. Can also contain a list of languages for a message containing more than one language. 2.2.11. Header Field: Content-Alternative Description: Alternative content available Applicable protocol: MIME [7] Status: work-in-progress Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 3297 [22] Related information: Information about the media features of alternative content formats available for the current message. G. Klyne, et al. Standards Track [Page 49]
RFC 4021 Mail and MIME Header Fields March 2005 2.2.12. Header Field: Content-MD5 Description: MD5 checksum of content Applicable protocol: MIME [7] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 1864 [6] Related information: Checksum of content to ensure that it has not been modified. 2.2.13. Header Field: Content-Duration Description: Time duration of content Applicable protocol: MIME [7] Status: standards-track Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 2424 [15] Related information: Time duration of body part content, in seconds (e.g., for audio message). 3. IANA Considerations Section 2 of this specification provides initial registrations of mail and MIME header fields in the "Permanent Message Header Field Registry", defined by registration procedures for message header fields [1]. G. Klyne, et al. Standards Track [Page 50]
RFC 4021 Mail and MIME Header Fields March 2005 4. Security Considerations No security considerations are introduced by this registration document beyond those already inherent in use of the mail message header fields referenced. 5. Acknowledgements Most of the information in this document has been derived from Jacob Palme's work in RFC 2076 [25] and subsequent updates [26]. The authors also gratefully acknowledge contributions and constructive input from Mark Nottingham, Bruce Lilly, Keith Moore, and Charles Lindsey (the mention of whom is not intended to imply their unqualified support for material herein). 6. References 6.1. Normative References [1] Klyne, G., Nottingham, M., and J. Mogul, "Registration Procedures for Message Header Fields", BCP 90, RFC 3864, September 2004. [2] Crocker, D., "Standard for the format of ARPA Internet text messages", STD 11, RFC 822, August 1982. [3] Hardcastle-Kille, S., "Mapping between X.400(1988) / ISO 10021 and RFC 822", RFC 1327, May 1992. [4] Costanzo, A., Robinson, D., and R. Ullmann, "Encoding Header Field for Internet Messages", RFC 1505, August 1993. [5] Alvestrand, H., "Tags for the Identification of Languages", RFC 1766, March 1995. [6] Myers, J. and M. Rose, "The Content-MD5 Header Field", RFC 1864, October 1995. [7] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [8] Palme, J. and A. Hopmann, "MIME E-mail Encapsulation of Aggregate Documents, such as HTML (MHTML)", RFC 2110, March 1997. [9] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. G. Klyne, et al. Standards Track [Page 51]
RFC 4021 Mail and MIME Header Fields March 2005 [10] Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay): Mapping between X.400 and RFC 822/MIME", RFC 2156, January 1998. [11] Troost, R., Dorner, S., and K. Moore, "Communicating Presentation Information in Internet Messages: The Content- Disposition Header Field", RFC 2183, August 1997. [12] Hansen, T. and G. Vaudreuil, "Message Disposition Notification", RFC 3798, May 2004. [13] Neufeld, G. and J. Baer, "The Use of URLs as Meta-Syntax for Core Mail List Commands and their Transport through Message Header Fields", RFC 2369, July 1998. [14] Vaudreuil, G. and G. Parsons, "Voice Profile for Internet Mail - version 2 (VPIMv2)", RFC 3801, June 2004. [15] Vaudreuil, G. and G. Parsons, "Content Duration MIME Header Definition", RFC 3803, June 2004. [16] Palme, J., Hopmann, A., and N. Shelness, "MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)", RFC 2557, March 1999. [17] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April 2001. [18] Resnick, P., "Internet Message Format", RFC 2822, April 2001. [19] Klyne, G., "Indicating Media Features for MIME Content", RFC 2912, September 2000. [20] Chandhok, R. and G. Wenger, "List-Id: A Structured Field and Namespace for the Identification of Mailing Lists", RFC 2919, March 2001. [21] Alvestrand, H., "Content Language Headers", RFC 3282, May 2002. [22] Klyne, G., Iwazaki, R., and D. Crocker, "Content Negotiation for Messaging Services based on Email", RFC 3297, July 2002. [23] Burger, E., Candell, E., Eliot, C., and G. Klyne, "Message Context for Internet Mail", RFC 3458, January 2003. [24] Miller, J., Krauskopf, T., Resnick, P. and W. Treese, "PICS Label Distribution Label Syntax and Communication Protocols", W3C Recommendation REC-PICS-labels, October 1996, <http://www.w3.org/TR/REC-PICS-labels>. G. Klyne, et al. Standards Track [Page 52]
RFC 4021 Mail and MIME Header Fields March 2005 6.2. Informative References [25] Palme, J., "Common Internet Message Headers", RFC 2076, February 1997. [26] Palme, J., "Common Internet Message Header Fields", Work in Progress. URIs [27] <http://www.ninebynine.org/IETF/Messaging/HdrRegistry/ Intro.html> Authors' Addresses Graham Klyne Image Bioinformatics Research Group Department of Zoology, University of Oxford South Parks Road, Oxford OX1 3PS, UK Phone: +44-(0)1865-281991 Fax: +44-(0)1865-310447 EMail: GK-IETF@ninebynine.org Jacob Palme Stockholm University/KTH Forum 100 Kista S-164 40 Sweden Phone: +46-8-16 16 67 Fax: +46-8-783 08 29 EMail: jpalme@dsv.su.se G. Klyne, et al. Standards Track [Page 53]
RFC 4021 Mail and MIME Header Fields March 2005 Full Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. G. Klyne, et al. Standards Track [Page 54]