RFC 4021
Registration of Mail and MIME Header Fields
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.
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 Applicable protocol: Mail [18] Status: obsolete Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 1327 [3] Related information: Indicates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.
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Description: Reference message to be replaced Applicable protocol: Mail [18] Status: obsolete Author/change controller: IETF (mailto:iesg@ietf.org) Internet Engineering Task Force Specification document(s): RFC 1327 [3] Related information: Reference to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'.
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.
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:'.
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.
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.
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].
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 content2.2.1. 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.
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.
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.
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.
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.
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.
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].
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.
[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>.
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
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