Internet Assigned Numbers Authority Message Headers Last Updated 2024-02-13 Available Formats [IMG] XML [IMG] HTML [IMG] 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 [RFC850][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 [RFC850][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 [RFC850][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] CFBL-Address mail [RFC9477] CFBL-Feedback-ID mail [RFC9477] 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] Wrong-Recipient prov/wrong-recipient mail [draft-dweekly-wrong-recipient-04] 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) 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