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 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.
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
Full Copyright Statement
Copyright (C) The Internet Society (2005).