   Internet Assigned Numbers Authority

                                                                   Message Headers

   Last Updated
           2022-06-08

   Available Formats
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           Plain text

   Registries included below

     * Permanent Message Header Field Names
     * Provisional Message Header Field Names
     * Content-Translation-Type Header Field Values

Permanent Message Header Field Names

   Registration Procedure(s)

 Expert Review

   Expert(s)

 Graham Klyne

   Reference
           [RFC3864]

   Note

 [RFC5504] specified that no new header fields be registered that begin with "Downgraded-".
 That restriction is now lifted, per [RFC6857].

   Note

 HTTP field name registrations have been moved to [https://www.iana.org/assignments/http-fields]
 per [RFC9110].


   Available Formats
           [IMG]
           CSV

             Header Field Name                   Template         Protocol    Status                          Reference
   Accept-Language                                                mail                   [RFC4021]
   Also-Control                                                   netnews  obsoleted     [RFC1849][RFC5536]
   Alternate-Recipient                                            mail                   [RFC4021]
   Approved                                                       netnews  standard      [RFC5536]
   ARC-Authentication-Results                                     mail     experimental  [RFC8617]
   ARC-Message-Signature                                          mail     experimental  [RFC8617]
   ARC-Seal                                                       mail     experimental  [RFC8617]
   Archive                                                        netnews  standard      [RFC5536]
   Archived-At                                                    mail     standard      [RFC5064]
   Archived-At                                                    netnews  standard      [RFC5064]
   Article-Names                                                  netnews  obsoleted     [RFC1849][RFC5536]
   Article-Updates                                                netnews  obsoleted     [RFC1849][RFC5536]
   Authentication-Results                                         mail     standard      [RFC8601]
   Auto-Submitted                                                 mail     standard      [RFC3834 section 5]
   Autoforwarded                                                  mail                   [RFC4021]
   Autosubmitted                                                  mail                   [RFC4021]
   Base                                                           MIME     obsoleted     [RFC1808][RFC2068 Section 14.11]
   Bcc                                                            mail     standard      [RFC5322]
   Body                                                           none     reserved      [RFC6068]
   Cancel-Key                                                     netnews  standard      [RFC8315]
   Cancel-Lock                                                    netnews  standard      [RFC8315]
   Cc                                                             mail     standard      [RFC5322]
   Comments                                                       mail     standard      [RFC5322]
   Comments                                                       netnews  standard      [RFC5536][RFC5322]
   Content-Alternative                                            MIME                   [RFC4021]
   Content-Base                                                   MIME     obsoleted     [RFC2110][RFC2557]
   Content-Description                                            MIME                   [RFC4021]
   Content-Disposition                                            MIME                   [RFC4021]
   Content-Duration                                               MIME                   [RFC4021]
   Content-features                                               MIME                   [RFC4021]
   Content-ID                                                     MIME                   [RFC4021]
   Content-Identifier                                             mail                   [RFC4021]
   Content-Language                                               MIME                   [RFC4021]
   Content-Location                                               MIME                   [RFC4021]
   Content-MD5                                                    MIME                   [RFC4021]
   Content-Return                                                 mail                   [RFC4021]
   Content-Transfer-Encoding                                      MIME                   [RFC4021]
   Content-Translation-Type                                       MIME     standard      [RFC8255]
   Content-Type                                                   MIME                   [RFC4021]
   Control                                                        netnews  standard      [RFC5536]
   Conversion                                                     mail                   [RFC4021]
   Conversion-With-Loss                                           mail                   [RFC4021]
   DL-Expansion-History                                           mail                   [RFC4021]
   Date                                                           mail     standard      [RFC5322]
   Date                                                           netnews  standard      [RFC5536][RFC5322]
   Date-Received                                                  netnews  obsoleted     [RFC0850][RFC5536]
   Deferred-Delivery                                              mail                   [RFC4021]
   Delivery-Date                                                  mail                   [RFC4021]
   Discarded-X400-IPMS-Extensions                                 mail                   [RFC4021]
   Discarded-X400-MTS-Extensions                                  mail                   [RFC4021]
   Disclose-Recipients                                            mail                   [RFC4021]
   Disposition-Notification-Options                               mail                   [RFC4021]
   Disposition-Notification-To                                    mail                   [RFC4021]
   Distribution                                                   netnews  standard      [RFC5536]
   DKIM-Signature                                                 mail     standard      [RFC6376]
   Downgraded-Bcc                                                 mail     obsoleted     [RFC5504][RFC6857]
   Downgraded-Cc                                                  mail     obsoleted     [RFC5504][RFC6857]
   Downgraded-Disposition-Notification-To                         mail     obsoleted     [RFC5504][RFC6857]
   Downgraded-Final-Recipient                                     mail     standard      [RFC6857 Section 3.1.10]
   Downgraded-From                                                mail     obsoleted     [RFC5504][RFC6857 Section 3.1.10]
   Downgraded-In-Reply-To                                         mail     standard      [RFC6857 Section 3.1.10]
   Downgraded-Mail-From                                           mail     obsoleted     [RFC5504][RFC6857 Section 3.1.10]
   Downgraded-Message-Id                                          mail     standard      [RFC6857 Section 3.1.10]
   Downgraded-Original-Recipient                                  mail     standard      [RFC6857 Section 3.1.10]
   Downgraded-Rcpt-To                                             mail     obsoleted     [RFC5504][RFC6857]
   Downgraded-References                                          mail     standard      [RFC6857 Section 3.1.10]
   Downgraded-Reply-To                                            mail     obsoleted     [RFC5504][RFC6857]
   Downgraded-Resent-Bcc                                          mail     obsoleted     [RFC5504][RFC6857]
   Downgraded-Resent-Cc                                           mail     obsoleted     [RFC5504][RFC6857]
   Downgraded-Resent-From                                         mail     obsoleted     [RFC5504][RFC6857]
   Downgraded-Resent-Reply-To                                     mail     obsoleted     [RFC5504][RFC6857]
   Downgraded-Resent-Sender                                       mail     obsoleted     [RFC5504][RFC6857]
   Downgraded-Resent-To                                           mail     obsoleted     [RFC5504][RFC6857]
   Downgraded-Return-Path                                         mail     obsoleted     [RFC5504][RFC6857]
   Downgraded-Sender                                              mail     obsoleted     [RFC5504][RFC6857]
   Downgraded-To                                                  mail     obsoleted     [RFC5504][RFC6857]
   Encoding                                                       mail                   [RFC4021]
   Encrypted                                                      mail                   [RFC4021]
   Expires                                                        mail                   [RFC4021]
   Expires                                                        netnews  standard      [RFC5536]
   Expiry-Date                                                    mail                   [RFC4021]
   Followup-To                                                    netnews  standard      [RFC5536]
   From                                                           mail     standard      [RFC5322][RFC6854]
   From                                                           netnews  standard      [RFC5536][RFC5322]
   Generate-Delivery-Report                                       mail                   [RFC4021]
   Importance                                                     mail                   [RFC4021]
   In-Reply-To                                                    mail     standard      [RFC5322]
   Incomplete-Copy                                                mail                   [RFC4021]
   Injection-Date                                                 netnews  standard      [RFC5536]
   Injection-Info                                                 netnews  standard      [RFC5536]
   Keywords                                                       mail     standard      [RFC5322]
   Keywords                                                       netnews  standard      [RFC5536][RFC5322]
   Language                                                       mail                   [RFC4021]
   Latest-Delivery-Time                                           mail                   [RFC4021]
   Lines                                                          netnews  deprecated    [RFC5536][RFC3977]
   List-Archive                                                   mail                   [RFC4021]
   List-Help                                                      mail                   [RFC4021]
   List-ID                                                        mail                   [RFC4021]
   List-Owner                                                     mail                   [RFC4021]
   List-Post                                                      mail                   [RFC4021]
   List-Subscribe                                                 mail                   [RFC4021]
   List-Unsubscribe                       perm/list-unsubscribe   mail                   [RFC4021]
   List-Unsubscribe-Post                                          mail     standard      [RFC8058]
   Message-Context                                                mail                   [RFC4021]
   Message-ID                                                     mail     standard      [RFC5322]
   Message-ID                                                     netnews  standard      [RFC5536][RFC5322]
   Message-Type                                                   mail                   [RFC4021]
   MIME-Version                                                   MIME                   [RFC4021]
   MMHS-Exempted-Address                                          mail                   [RFC6477][ACP123 Appendix A1.1 and Appendix B.105]
   MMHS-Extended-Authorisation-Info                               mail                   [RFC6477][ACP123 Appendix A1.2 and Appendix B.106]
   MMHS-Subject-Indicator-Codes                                   mail                   [RFC6477][ACP123 Appendix A1.3 and Appendix B.107]
   MMHS-Handling-Instructions                                     mail                   [RFC6477][ACP123 Appendix A1.4 and Appendix B.108]
   MMHS-Message-Instructions                                      mail                   [RFC6477][ACP123 Appendix A1.5 and Appendix B.109]
   MMHS-Codress-Message-Indicator                                 mail                   [RFC6477][ACP123 Appendix A1.6 and Appendix B.110]
   MMHS-Originator-Reference                                      mail                   [RFC6477][ACP123 Appendix A1.7 and Appendix B.111]
   MMHS-Primary-Precedence                                        mail                   [RFC6477][ACP123 Appendix A1.8 and Appendix B.101]
   MMHS-Copy-Precedence                                           mail                   [RFC6477][ACP123 Appendix A1.9 and Appendix B.102]
   MMHS-Message-Type                                              mail                   [RFC6477][ACP123 Appendix A1.10 and Appendix B.103]
   MMHS-Other-Recipients-Indicator-To                             mail                   [RFC6477][ACP123 Appendix A1.12 and Appendix B.113]
   MMHS-Other-Recipients-Indicator-CC                             mail                   [RFC6477][ACP123 Appendix A1.12 and Appendix B.113]
   MMHS-Acp127-Message-Identifier                                 mail                   [RFC6477][ACP123 Appendix A1.14 and Appendix B.116]
   MMHS-Originator-PLAD                                           mail                   [RFC6477][ACP123 Appendix A1.15 and Appendix B.117]
   MT-Priority                                                    mail     standard      [RFC6758]
   Newsgroups                                                     netnews  standard      [RFC5536]
   NNTP-Posting-Date                                              netnews  obsoleted     [RFC5536]
   NNTP-Posting-Host                                              netnews  obsoleted     [RFC2980][RFC5536]
   Obsoletes                                                      mail                   [RFC4021]
   Organization                                                   mail     informational [RFC7681]
   Organization                                                   netnews  standard      [RFC5536]
   Original-Encoded-Information-Types                             mail                   [RFC4021]
   Original-From                                                  mail     standard      [RFC5703]
   Original-Message-ID                                            mail                   [RFC4021]
   Original-Recipient                     perm/original-recipient mail     standard      [RFC3798][RFC5337]
   Original-Sender                                                netnews  standard      [RFC5537]
   Originator-Return-Address                                      mail                   [RFC4021]
   Original-Subject                                               mail     standard      [RFC5703]
   Path                                                           netnews  standard      [RFC5536]
   PICS-Label                                                     mail                   [RFC4021]
   Posting-Version                                                netnews  obsoleted     [RFC0850][RFC5536]
   Prevent-NonDelivery-Report                                     mail                   [RFC4021]
   Priority                                                       mail                   [RFC4021]
   Received                                                       mail     standard      [RFC5322][RFC5321]
   Received-SPF                                                   mail     standard      [RFC7208]
   References                                                     mail     standard      [RFC5322]
   References                                                     netnews  standard      [RFC5536][RFC5322]
   Relay-Version                                                  netnews  obsoleted     [RFC0850][RFC5536]
   Reply-By                                                       mail                   [RFC4021]
   Reply-To                                                       mail     standard      [RFC5322]
   Reply-To                                                       netnews  standard      [RFC5536][RFC5322]
   Require-Recipient-Valid-Since                                  mail     standard      [RFC7293]
   Resent-Bcc                                                     mail     standard      [RFC5322]
   Resent-Cc                                                      mail     standard      [RFC5322]
   Resent-Date                                                    mail     standard      [RFC5322]
   Resent-From                                                    mail     standard      [RFC5322][RFC6854]
   Resent-Message-ID                                              mail     standard      [RFC5322]
   Resent-Reply-To                                                mail     obsoleted     [RFC5322]
   Resent-Sender                                                  mail     standard      [RFC5322][RFC6854]
   Resent-To                                                      mail     standard      [RFC5322]
   Return-Path                                                    mail     standard      [RFC5322]
   See-Also                                                       netnews  obsoleted     [RFC1849][RFC5536]
   Sender                                                         mail     standard      [RFC5322][RFC6854]
   Sender                                                         netnews  standard      [RFC5536][RFC5322]
   Sensitivity                                                    mail                   [RFC4021]
   Solicitation                                                   mail                   [RFC3865]
   Subject                                                        mail     standard      [RFC5322]
   Subject                                                        netnews  standard      [RFC5536][RFC5322]
   Summary                                                        netnews  standard      [RFC5536]
   Supersedes                                                     mail                   [RFC4021]
   Supersedes                                                     netnews  standard      [RFC5536][RFC2156]
   TLS-Report-Domain                                              mail     standard      [RFC8460]
   TLS-Report-Submitter                                           mail     standard      [RFC8460]
   TLS-Required                                                   mail     standard      [RFC8689]
   To                                                             mail     standard      [RFC5322]
   User-Agent                                                     netnews  standard      [RFC5536][RFC2616]
   VBR-Info                                                       mail     standard      [RFC5518]
   X400-Content-Identifier                                        mail                   [RFC4021]
   X400-Content-Return                                            mail                   [RFC4021]
   X400-Content-Type                                              mail                   [RFC4021]
   X400-MTS-Identifier                                            mail                   [RFC4021]
   X400-Originator                                                mail                   [RFC4021]
   X400-Received                                                  mail                   [RFC4021]
   X400-Recipients                                                mail                   [RFC4021]
   X400-Trace                                                     mail                   [RFC4021]
   Xref                                                           netnews  standard      [RFC5536]

Provisional Message Header Field Names

   Registration Procedure(s)

 Expert Review

   Expert(s)

 Graham Klyne

   Reference
           [RFC3864]

   Note

 Registration of a Provisional Message Header Field does not of itself imply any kind of
 endorsement by the IETF, IANA or any other body.

   Note

 HTTP field name registrations have been moved to [https://www.iana.org/assignments/http-fields]
 per [RFC-ietf-httpbis-semantics-19].


   Available Formats
           [IMG]
           CSV

     Header Field Name          Template      Protocol   Status                                        Reference
  Apparently-To            prov/apparently-to mail                [RFC2076]
  Author                                      mail                [RFC9057]
  Delivered-To                                mail                [RFC9228]
  EDIINT-Features                             mail                [RFC6017]
  Eesst-Version                               mail                [RFC7681]
  Errors-To                prov/errors-to     mail                [RFC2076]
  Form-Sub                                    mail                [draft-levine-mailbomb-header]
  Jabber-ID                prov/jabber-id     mail                [RFC7259]
  Jabber-ID                prov/jabber-id     netnews             [RFC7259]
  MMHS-Authorizing-Users                      mail                [RFC7912]
  Privicon                                    mail                [draft-koenig-privicons]
  SIO-Label                                   mail                [RFC7444]
  SIO-Label-History                           mail                [RFC7444]
  X-Archived-At            prov/x-archived-at mail     deprecated [RFC5064]
  X-Archived-At            prov/x-archived-at netnews  deprecated [RFC5064]
  X-Mittente                                  mail                [RFC6109]
  X-PGP-Sig                prov/x-pgp-sig     netnews             [ftp://ftp.isc.org/pub/pgpcontrol/FORMAT][https://ftp.isc.org/pub/pgpcontrol/FORMAT]
  X-Ricevuta                                  mail                [RFC6109]
  X-Riferimento-Message-ID                    mail                [RFC6109]
  X-TipoRicevuta                              mail                [RFC6109]
  X-Trasporto                                 mail                [RFC6109]
  X-VerificaSicurezza                         mail                [RFC6109]

Content-Translation-Type Header Field Values

   Registration Procedure(s)

 Specification Required

   Expert(s)

 Nathaniel Borenstein, Nik Tomkinson

   Reference
           [RFC8255]

   Available Formats
           [IMG]
           CSV

     Value                                                       Description                                                      Reference
   original  Content in the original language                                                                                     [RFC8255]
   human     Content that has been translated by a human translator or a human has checked and corrected an automated translation [RFC8255]
   automated Content that has been translated by an electronic agent without proofreading or subsequent correction                [RFC8255]

   Licensing Terms
