2013-03-14 Expert Review Graham Klyne specified that no new header fields be registered that begin with "Downgraded-". That restriction is now lifted, per . A-IM http Accept http Accept-Additions http Accept-Charset http Accept-Encoding http Accept-Features http Accept-Language http Accept-Language mail Accept-Patch http Accept-Ranges http Age http Allow http Also-Control netnews obsoleted Son-of-1036 Alternate-Recipient mail Alternates http Apply-To-Redirect-Ref http Approved netnews standard Archive netnews standard prov/archived-at Archived-At mail standard prov/archived-at Archived-At netnews standard Article-Names netnews obsoleted Son-of-1036 Article-Updates netnews obsoleted Son-of-1036 Authentication-Info http Authentication-Results mail standard Authorization http Auto-Submitted mail standard RFC3834 section 5 Autoforwarded mail Autosubmitted mail Base MIME obsoleted RFC2068 Section 14.11 Bcc mail standard Body none reserved C-Ext http C-Man http C-Opt http C-PEP http C-PEP-Info http Cache-Control http Cc mail standard Comments mail standard Comments netnews standard Connection http Content-Alternative MIME Content-Base http obsoleted Content-Base MIME obsoleted Content-Description MIME Content-Disposition http standard Content-Disposition MIME Content-Duration MIME Content-Encoding http Content-features MIME Content-ID http Content-ID MIME Content-Identifier mail Content-Language http Content-Language MIME Content-Length http Content-Location http Content-Location MIME Content-MD5 http Content-MD5 MIME Content-Range http Content-Return mail Content-Script-Type http Content-Style-Type http Content-Transfer-Encoding MIME Content-Type http Content-Type MIME Content-Version http Control netnews standard Conversion mail Conversion-With-Loss mail Cookie http standard Cookie2 http obsoleted DASL http standard DAV http standard DL-Expansion-History mail Date http Date mail standard Date netnews standard Date-Received netnews obsoleted Default-Style http Deferred-Delivery mail Delivery-Date mail Delta-Base http Depth http standard Derived-From http Destination http standard Differential-ID http Digest http Discarded-X400-IPMS-Extensions mail Discarded-X400-MTS-Extensions mail Disclose-Recipients mail Disposition-Notification-Options mail Disposition-Notification-To mail Distribution netnews standard DKIM-Signature mail standard Downgraded-Bcc mail obsoleted Downgraded-Cc mail obsoleted Downgraded-Disposition-Notification-To mail obsoleted Downgraded-Final-Recipient mail standard RFC6857 Section 3.1.10 Downgraded-From mail obsoleted RFC6857 Section 3.1.10 Downgraded-In-Reply-To mail standard RFC6857 Section 3.1.10 Downgraded-Mail-From mail obsoleted 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 Downgraded-References mail standard RFC6857 Section 3.1.10 Downgraded-Reply-To mail obsoleted Downgraded-Resent-Bcc mail obsoleted Downgraded-Resent-Cc mail obsoleted Downgraded-Resent-From mail obsoleted Downgraded-Resent-Reply-To mail obsoleted Downgraded-Resent-Sender mail obsoleted Downgraded-Resent-To mail obsoleted Downgraded-Return-Path mail obsoleted Downgraded-Sender mail obsoleted Downgraded-To mail obsoleted Encoding mail Encrypted mail ETag http Expect http Expires http Expires mail Expires netnews standard Expiry-Date mail Ext http Followup-To netnews standard Forwarded http standard From http From mail standard From netnews standard Generate-Delivery-Report mail GetProfile http Host http IM http If http standard If-Match http If-Modified-Since http If-None-Match http If-Range http If-Schedule-Tag-Match http standard If-Unmodified-Since http Importance mail In-Reply-To mail standard Incomplete-Copy mail Injection-Date netnews standard Injection-Info netnews standard Keep-Alive http Keywords mail standard Keywords netnews standard Label http Language mail Last-Modified http Latest-Delivery-Time mail Lines netnews deprecated Link http List-Archive mail List-Help mail List-ID mail List-Owner mail List-Post mail List-Subscribe mail List-Unsubscribe mail Location http Lock-Token http standard Man http Max-Forwards http Message-Context mail Message-ID mail standard Message-ID netnews standard Message-Type mail Meter http MIME-Version http MIME-Version MIME MMHS-Exempted-Address mail ACP123 Appendix A1.1 and Appendix B.105 MMHS-Extended-Authorisation-Info mail ACP123 Appendix A1.2 and Appendix B.106 MMHS-Subject-Indicator-Codes mail ACP123 Appendix A1.3 and Appendix B.107 MMHS-Handling-Instructions mail ACP123 Appendix A1.4 and Appendix B.108 MMHS-Message-Instructions mail ACP123 Appendix A1.5 and Appendix B.109 MMHS-Codress-Message-Indicator mail ACP123 Appendix A1.6 and Appendix B.110 MMHS-Originator-Reference mail ACP123 Appendix A1.7 and Appendix B.111 MMHS-Primary-Precedence mail ACP123 Appendix A1.8 and Appendix B.101 MMHS-Copy-Precedence mail ACP123 Appendix A1.9 and Appendix B.102 MMHS-Message-Type mail ACP123 Appendix A1.10 and Appendix B.103 MMHS-Other-Recipients-Indicator-To mail ACP123 Appendix A1.12 and Appendix B.113 MMHS-Other-Recipients-Indicator-CC mail ACP123 Appendix A1.12 and Appendix B.113 MMHS-Acp127-Message-Identifier mail ACP123 Appendix A1.14 and Appendix B.116 MMHS-Originator-PLAD mail ACP123 Appendix A1.15 and Appendix B.117 MT-Priority mail standard Negotiate http Newsgroups netnews standard NNTP-Posting-Date netnews obsoleted NNTP-Posting-Host netnews obsoleted Obsoletes mail Opt http Ordering-Type http standard Organization netnews standard Origin http standard Original-Encoded-Information-Types mail Original-From mail standard Original-Message-ID mail perm/original-recipient Original-Recipient mail standard Original-Sender netnews standard Originator-Return-Address mail Original-Subject mail standard Overwrite http standard P3P http Path netnews standard PEP http PICS-Label http PICS-Label mail Pep-Info http Position http standard Posting-Version netnews obsoleted Pragma http Prefer http standard Preference-Applied http standard Prevent-NonDelivery-Report mail Priority mail ProfileObject http Protocol http Protocol-Info http Protocol-Query http Protocol-Request http Proxy-Authenticate http Proxy-Authentication-Info http Proxy-Authorization http Proxy-Features http Proxy-Instruction http Public http Range http Received mail standard Received-SPF mail Redirect-Ref http References mail standard References netnews standard Referer http Relay-Version netnews obsoleted Reply-By mail Reply-To mail standard Reply-To netnews standard Resent-Bcc mail standard Resent-Cc mail standard Resent-Date mail standard Resent-From mail standard Resent-Message-ID mail standard Resent-Reply-To mail obsoleted Resent-Sender mail standard Resent-To mail standard Retry-After http Return-Path mail standard Safe http Schedule-Reply http standard Schedule-Tag http standard Sec-WebSocket-Accept http standard Sec-WebSocket-Extensions http standard Sec-WebSocket-Key http standard Sec-WebSocket-Protocol http standard Sec-WebSocket-Version http standard Security-Scheme http See-Also netnews obsoleted Son-of-1036 Sender mail standard Sender netnews standard Sensitivity mail Server http Set-Cookie http standard Set-Cookie2 http obsoleted SetProfile http SLUG http standard SoapAction http Solicitation mail Status-URI http Strict-Transport-Security http standard Subject mail standard Subject netnews standard Summary netnews standard Supersedes mail Supersedes netnews standard Surrogate-Capability http Surrogate-Control http TCN http TE http Timeout http standard To mail standard Trailer http Transfer-Encoding http URI http Upgrade http User-Agent http User-Agent netnews standard Variant-Vary http Vary http VBR-Info mail standard Via http WWW-Authenticate http Want-Digest http Warning http X400-Content-Identifier mail X400-Content-Return mail X400-Content-Type mail X400-MTS-Identifier mail X400-Originator mail X400-Received mail X400-Recipients mail X400-Trace mail Xref netnews standard Expert Review Graham Klyne Registration of a Provisional Message Header Field does not of itself imply any kind of endorsement by the IETF, IANA or any other body. prov/accept-datetime Accept-Datetime http www.mementoweb.org/guide www.mementoweb.org/guide/http prov/access-control Access-Control http deprecated W3C Web Application Formats Working Group prov/access-control-allow-credentials Access-Control-Allow-Credentials http W3C Web Application Formats Working Group prov/access-control-allow-headers Access-Control-Allow-Headers http W3C Web Application Formats Working Group prov/access-control-allow-methods Access-Control-Allow-Methods http W3C Web Application Formats Working Group prov/access-control-allow-origin Access-Control-Allow-Origin http W3C Web Application Formats Working Group prov/access-control-max-age Access-Control-Max-Age http W3C Web Application Formats Working Group prov/access-control-request-method Access-Control-Request-Method http W3C Web Application Formats Working Group prov/access-control-request-headers Access-Control-Request-Headers http W3C Web Application Formats Working Group prov/apparently-to Apparently-To mail Compliance http Content-Transfer-Encoding http Cost http EDIINT-Features http EDIINT-Features mail prov/errors-to Errors-To mail prov/jabber-id Jabber-ID mail prov/jabber-id Jabber-ID netnews prov/memento-datetime Memento-Datetime http www.mementoweb.org/guide/quick-intro www.mementoweb.org/guide/rfc/ID Message-ID http prov/method-check Method-Check http deprecated W3C Web Application Formats Working Group prov/method-check-expires Method-Check-Expires http deprecated W3C Web Application Formats Working Group Non-Compliance http Optional http Privicon mail prov/referer-root Referer-Root http deprecated W3C Web Application Formats Working Group Resolution-Hint http Resolver-Location http SubOK http Subst http Title http UA-Color http UA-Media http UA-Pixels http UA-Resolution http UA-Windowpixels http Version http prov/x-archived-at X-Archived-At mail deprecated prov/x-archived-at X-Archived-At netnews deprecated prov/x-device-accept X-Device-Accept http W3C Mobile Web Best Practices Working Group prov/x-device-accept-charset X-Device-Accept-Charset http W3C Mobile Web Best Practices Working Group prov/x-device-accept-encoding X-Device-Accept-Encoding http W3C Mobile Web Best Practices Working Group prov/x-device-accept-language X-Device-Accept-Language http W3C Mobile Web Best Practices Working Group prov/x-device-user-agent X-Device-User-Agent http W3C Mobile Web Best Practices Working Group X-Mittente mail X-Ricevuta mail X-Riferimento-Message-ID mail X-TipoRicevuta mail X-Trasporto mail X-VerificaSicurezza mail