Email Author Header Field
draft-crocker-email-author-03

Network Working Group                                         D. Crocker
Internet-Draft                               Brandenburg InternetWorking
Intended status: Experimental                             March 20, 2021
Expires: September 21, 2021

                       Email Author Header Field
                     draft-crocker-email-author-03

Abstract

   Internet mail defines the From: header field to indicate the author
   of the message's content and the Sender: field to indicate who
   initially handled the message, on the author's behalf.  The Sender:
   field is optional, if it has the same information as the From: field.
   This was not a problem, until development of stringent protections on
   use of the From: field.  It has prompted Mediators, such as mailing
   lists, to modify the From: field, to circumvent mail rejection caused
   by those protections.  In effect, the From: field has become
   dominated by its role as a handling identifier.

   The current specification augments the altered use of the From:
   field, by specifying the Author: field, which ensures identification
   of the original author of the message and is not subject to
   modification by Mediators.  This version is published as an
   Experiment, to assess community interest, functional efficacy, and
   technical adequacy.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on September 21, 2021.

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Copyright Notice

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Author Header Field . . . . . . . . . . . . . . . . . . . . .   4
   4.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Experimental Goals  . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Internet mail conducts asynchronous communication from an author to
   one or more recipients, and is used for ongoing dialogue amongst
   them.  Email has a long history of serving a wide range of human uses
   and styles, within that simple framework, and the mechanisms for
   making email robust and safe serve that sole purpose.

   Internet mail defines the content header's From: field to indicate
   the author of the message and the Sender: field to indicate who
   initially handled the message, on the author's behalf.  [Mail-Fmt]
   The Sender: field is optional, if it has the same information as the
   From: field.  That is, when the Sender: field is absent, the From:
   field has conflated semantics, as both a handling identifier and a
   content creator identifier.  These fields were initially defined in
   [RFC733] and making the redundant Sender: field optional was a small,
   obvious optimization, in the days of slower communications, expensive
   storage and less powerful computers.

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   The dual semantics was not a problem, until development of stringent
   protections on use of the From: field.  It has prompted Mediators,
   such as mailing lists, to modify the From: field, to circumvent
   receiver mail rejection, caused by those protections.  This affects
   end-to-end usability of email, between the author and the final
   recipients, because mail received from the same author is treated
   differently by the recipient's software, depending on what path the
   message followed.

   By way of example, mail originating with:

   From:  Example User <user@example.com>

   which is sent directly to a recipient, will show the author's display
   name correctly and can correctly analyze, filter and aggregate mail
   from the author, based on their email address.  However if the author
   sends through a mailing list, and the mailing list conducts a common
   form of From: modification, needed to bypass enforcement of stringent
   authentication policies, then the received message might instead have
   a From: field showing:

   From: Example User via Example List <listname@list.example.org>

   The change inserts an operational address, for the Mediator, into the
   From: field, and distorts the field's display-name, as a means of
   recording the modification.

   In terms of email identification semantics, this is a profound
   change:

   o  The result is that the recipient's software will see the message
      as being from an entirely different author and will handle it
      separately, such as for sorting or filtering.  In effect, the
      recipient's software will see the same person's email as being
      from a different address, for the person's actual address and each
      of the mailing lists that person's mail transits.

   o  Mediators might create a Reply-To: field, with the original From:
      field email address.  This facilitates getting replies back to the
      original author, but it does nothing to aid other processing or
      presentation, done by the recipient's Mail User Agent (MUA), based
      on what it believes is the author's address or original display-
      name.  This Reply-To action represents another knock-on,
      collateral damage, by distorting the meaning of that header field,
      as well as creating an issue if the field already exists.

   In effect, the From: field has become dominated by its role as a
   handling identifier.  The current specification augments this altered

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   use of the From: field, by specifying the Author: field, which
   identifies the original author of the message and is not subject to
   modification by Mediators.

   While it might be cleanest to move towards more reliable use of the
   Sender: field and then to target it as the focus of authentication
   concerns, enhancement of existing standards works best with
   incremental additions, rather than with efforts at replacement.  To
   that end, this specification provides a means of supplying author
   information that is not subject to modification by processes seeking
   to enforce stringent authentication.

   This version is published as an Experiment, to assess community
   interest, functional efficacy, and technical adequacy.  See
   Section 7.

2.  Terminology

   Terminology and architectural details in this document are
   incorporated from [Mail-Arch].

   Normative language, per [RFC8174]:

      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
      NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
      "MAY", and "OPTIONAL" in this document are to be interpreted as
      described in BCP 14 [RFC2119] [RFC8174] when, and only when, they
      appear in all capitals, as shown here.

   RFC EDITOR: Please remove for publication:

      Discussion of this draft is directed to the ietf-822@ietf.org
      mailing list.

3.  Author Header Field

   A new message header field is defined: Author:. It has the same
   syntax as the From: header field [Mail-Fmt].  As with the original
   and primary intent for the From: field, the Author: field is to
   contain the email address of the author of the message content.  It
   also can contain the displayable human name of the author.

   The [ABNF] for the field's syntax is:

   author = "Author:" mailbox-list CRLF

   which echos the syntax for the From: header field.

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   This header field can be added as part of the original message
   creation process, or it can be added later, by a Mediator, to
   preserve the original author information from the From: field.

   The goal of the Author: field is to reflect information about the
   original author.  However it is possible that the author's MUA or
   Mail Submission Agent (MSA) will not create it, but that a Mediator
   might know it will be modifying the From: field and wish to preserve
   author information.  Hence it needs to be allowed to create the
   Author: field for this, if the field does not already exist.

   Processing of the Author: field follows these rules:

   o  If an Author: field already exists, a new one MUST NOT be created
      and the existing one MUST NOT be modified

   o  An author's MUA or MSA MAY create an Author: field, and its value
      MUST be identical to the value in the From: field

   o  A Mediator MAY create an Author: field, if one does not already
      exist, and this new field's value MUST be identical to the value
      of the From: field, at the time the Mediator received the message
      (and before the Mediator causes any changes to the From: field)

4.  Discussion

   The Author: header field, here, is intended for creation during
   message generation or during mediation.  It is intended for use by
   recipient MUAs, as they typically use the From: field.  In that
   regard, it would be reasonable for an MUA that would normally
   organize, filter, or display information based on the From: field to
   give the Author: header field preference.

   Original-From: is a similar header field, referenced in [RFC5703].
   It is registered with IANA, which cites RFC5703 as the controlling
   source for the entry.  However that document only has a minimal
   definition for the field.  Also, the field is solely intended for use
   by Mediators, to preserve information from a modified From:. The
   current specification can be used either during origination or during
   mediation.

   While the basic model of email header fields is highly extensible,
   there well might be implementation and usability considerations for
   carrying this field through to end-users, such as via [IMAP].

   Obviously any security-related processing of a message needs to
   distinguish From: from Author: and treat their information
   accordingly.

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5.  Security Considerations

   Any header field containing identification information is a source of
   security and privacy concerns, especially when the information
   pertains to content authorship.  Generally, the handling of the
   Author: header field needs to receive scrutiny and care, comparable
   to that given to the From: header field, but preferably not in a way
   that defeats its utility.

   Given the semantics of this field, it is easy to believe that use of
   this field will create a new attack vector for tricking end-users.
   However (and perhaps surprisingly) for all of the real and serious
   demonstration of users' being tricked by deceptive or false content
   in a message, there is no evidence that problematic content in a
   header field, which is providing information about message's author,
   directly contributes to differential and problematic behavior by the
   end user.  (The presents an obvious exercise for the reader, to find
   credible, documented evidence.)

6.  IANA Considerations

   The IANA is request to register the Author header field, per
   [RFC3864], into the "Permanent Message Header Field Registry":

      Header field name: Author

      Applicable protocol: mail

      Status: Experimental

      Author/Change controller: Dave Crocker <dcrocker@bbiw.net>

      Specification document(s): *** This document ***

7.  Experimental Goals

   Given that the semantics of this field echo the long-standing From:
   field, the basic mechanics of the field's creation and use are well
   understood.  Points of concern, therefore, are with possible
   interactions with the existing From: field, with anti-abuse systems,
   and with MUA behavior, along with basic market acceptance.  So the
   questions to answer, while the header field has experimental status
   are:

   o  Is there demonstrated interest by MUA developers?

   o  If MUA developers add this capability, is it used by authors?

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   o  Does the presence of the Author field, in combination with the
      From field, create any operational problems, especially for
      recipients?

   o  Does the presence of the Author field demonstrate additional
      security issues?

   o  Does the presence of the Author field engender problematic
      behavior by anti-abuse software, such as defeating its utility?

8.  References

8.1.  Normative References

   [ABNF]     Dave, D., Ed. and P. Paul, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 5234, January 2008.

   [Mail-Arch]
              Crocker, D., "Internet Mail Architecture", RFC 5598, July
              2009.

   [Mail-Fmt]
              Resnick, P., Ed., "Internet Message Format", RFC 5322,
              October 2008.

   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              DOI 10.17487/RFC3864, September 2004,
              <https://www.rfc-editor.org/info/rfc3864>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

8.2.  Informative References

   [IMAP]     Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
              <https://www.rfc-editor.org/info/rfc3501>.

   [RFC5703]  Hansen, T. and C. Daboo, "Sieve Email Filtering: MIME Part
              Tests, Iteration, Extraction, Replacement, and Enclosure",
              RFC 5703, October 2009.

   [RFC733]   Crocker, D., Vittal, J., Pogran, K., and D. Henderson,
              "Standard for the Format of ARPA Network Text Messages",
              RFC 733, November 1977.

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Appendix A.  Acknowledgements

   The idea for this field was prompted by discussions in the IETF's
   DMARC working group, with participation including: Benny Lyne
   Amorsen, Kurt Anderson, Laura Atkins, Adrian Farrel, Murray S.
   Kucherawy, Mike Hammer, John Levine, Alexey Melnikov, Jesse Thompson,
   Alessandro Vesely.

Author's Address

   Dave Crocker
   Brandenburg InternetWorking

   Email: dcrocker@bbiw.net

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