Message Headers
Message Headers
2025-08-25
Available Formats
XML
HTML
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)
Mark Baker (primary), Murray Kucherawy (backup)
Reference
RFC3864
][
RFC-ietf-emailcore-rfc5322bis-12
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 [
per [
RFC9110
].
Available Formats
CSV
Header Field Name
Template
Protocol
Status
Trace
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
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.3
Body
none
reserved
RFC6068
Cancel-Key
netnews
standard
RFC8315
Cancel-Lock
netnews
standard
RFC8315
Cc
mail
standard
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.3
Comments
mail
standard
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.5
Comments
netnews
standard
RFC5536
][
RFC-ietf-emailcore-rfc5322bis-12
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
][
RFC9788
Control
netnews
standard
RFC5536
Conversion
mail
RFC4021
Conversion-With-Loss
mail
RFC4021
DL-Expansion-History
mail
RFC4021
Date
mail
standard
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.1
Date
netnews
standard
RFC5536
][
RFC-ietf-emailcore-rfc5322bis-12
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
no
RFC6854
][
RFC-ietf-emailcore-rfc5322bis-12, 3.6.2
From
netnews
standard
RFC5536
][
RFC-ietf-emailcore-rfc5322bis-12
Generate-Delivery-Report
mail
RFC4021
HP-Outer
mail
standard
RFC9788 Section 2.2.1
Importance
mail
RFC4021
In-Reply-To
mail
standard
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.4
Incomplete-Copy
mail
RFC4021
Injection-Date
netnews
standard
RFC5536
Injection-Info
netnews
standard
RFC5536
Keywords
mail
standard
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.5
Keywords
netnews
standard
RFC5536
][
RFC-ietf-emailcore-rfc5322bis-12
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
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.4
Message-ID
netnews
standard
RFC5536
][
RFC-ietf-emailcore-rfc5322bis-12
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
yes
RFC-ietf-emailcore-rfc5322bis-12, 3.6.7
][
RFC-ietf-emailcore-rfc5321bis-43
Received-SPF
mail
standard
RFC7208
References
mail
standard
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.4
References
netnews
standard
RFC5536
][
RFC-ietf-emailcore-rfc5322bis-12
Relay-Version
netnews
obsoleted
RFC850
][
RFC5536
Reply-By
mail
RFC4021
Reply-To
mail
standard
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.2
Reply-To
netnews
standard
RFC5536
][
RFC-ietf-emailcore-rfc5322bis-12
Require-Recipient-Valid-Since
mail
standard
RFC7293
Resent-Bcc
mail
standard
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.6
Resent-Cc
mail
standard
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.6
Resent-Date
mail
standard
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.6
Resent-From
mail
standard
no
RFC6854
][
RFC-ietf-emailcore-rfc5322bis-12, 3.6.6
Resent-Message-ID
mail
standard
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.6
Resent-Reply-To
mail
obsoleted
no
RFC-ietf-emailcore-rfc5322bis-12, 4.5.6
Resent-Sender
mail
standard
no
RFC6854
][
RFC-ietf-emailcore-rfc5322bis-12, 3.6.6
Resent-To
mail
standard
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.6
Return-Path
mail
standard
yes
RFC-ietf-emailcore-rfc5322bis-12, 3.6.7
][
RFC-ietf-emailcore-rfc5321bis-43
See-Also
netnews
obsoleted
RFC1849
][
RFC5536
Sender
mail
standard
no
RFC6854
][
RFC-ietf-emailcore-rfc5322bis-12, 3.6.2
Sender
netnews
standard
RFC5536
][
RFC-ietf-emailcore-rfc5322bis-12
Sensitivity
mail
RFC4021
Solicitation
mail
RFC3865
Subject
mail
standard
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.5
Subject
netnews
standard
RFC5536
][
RFC-ietf-emailcore-rfc5322bis-12
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
no
RFC-ietf-emailcore-rfc5322bis-12, 3.6.3
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)
Mark Baker (primary), Murray Kucherawy (backup)
Reference
RFC3864
][
RFC-ietf-emailcore-rfc5322bis-12
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 [
per [
RFC9110
].
Available Formats
CSV
Header Field Name
Template
Protocol
Status
Trace
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
Face
prov/face
mail
Face
prov/face
netnews
Form-Sub
mail
draft-levine-mailbomb-header-00
Jabber-ID
prov/jabber-id
mail
RFC7259
Jabber-ID
prov/jabber-id
netnews
RFC7259
MMHS-Authorizing-Users
mail
RFC7912
Privicon
mail
draft-koenig-privicons-01
SIO-Label
mail
RFC7444
SIO-Label-History
mail
RFC7444
Wrong-Recipient
prov/wrong-recipient
mail
draft-ietf-mailmaint-wrong-recipient-00
X-Archived-At
prov/x-archived-at
mail
deprecated
RFC5064
X-Archived-At
prov/x-archived-at
netnews
deprecated
RFC5064
X-Face
prov/x-face
mail
X-Face
prov/x-face
netnews
X-Mittente
mail
RFC6109
X-PGP-Sig
prov/x-pgp-sig
netnews
ftp://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
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