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RFC 4021

Registration of Mail and MIME Header Fields

Pages: 54
Proposed Standard
Updated by:  5322
Part 1 of 2 – Pages 1 to 25
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Top   ToC   RFC4021 - Page 1
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
Top   ToC   RFC4021 - Page 2
             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
Top   ToC   RFC4021 - Page 3
             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.
Top   ToC   RFC4021 - Page 4
   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
Top   ToC   RFC4021 - Page 5
   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?
Top   ToC   RFC4021 - Page 6
   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.
Top   ToC   RFC4021 - Page 7

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.
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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.
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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.
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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.
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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.
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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.
Top   ToC   RFC4021 - Page 13

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.
Top   ToC   RFC4021 - Page 14

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.
Top   ToC   RFC4021 - Page 15

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.
Top   ToC   RFC4021 - Page 16

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.
Top   ToC   RFC4021 - Page 17

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.
Top   ToC   RFC4021 - Page 18

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.
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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.
Top   ToC   RFC4021 - Page 20

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.
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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.
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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.
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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.
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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.
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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.)