Network Working Group                                         D. Crocker
Internet-Draft                               Brandenburg InternetWorking
Intended status: Informational                                 R. Signes
Expires: April 25, 2021                                         Fastmail
                                                                N. Freed
                                                        October 22, 2020

            React: Indicating Summary Reaction to a Message


   The popularity of social media has led to user comfort with easily
   signaling basic reactions to an author's posting, such as with a
   'thumbs up' or 'smiley' graphic indication.  This specification
   permits a similar facility for Internet Mail.

Status of This Memo

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   This Internet-Draft will expire on April 25, 2021.

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Reaction Content-Disposition  . . . . . . . . . . . . . . . .   3
   3.  Usability Considerations  . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The popularity of social media has led to user comfort with easily
   signaling summary reactions to an author's posting, by marking basic
   emoji graphics, such as with a 'thumbs up', 'heart', or 'smiley'
   indication.  Sometimes the permitted repertoire is constrained to a
   small set and sometimes a more extensive range of indicators is

   This specification defines a similar facility for Internet Mail.

   While it is already possible to include symbols and graphics as part
   of an email reply's content, there has not been an established means
   of signalling the semantic substance that such data are to be taken
   as a summary 'reaction' to the original message.  That is, a
   mechanism to identify symbols as specifically providing a summary
   reaction to the cited message, rather than merely being part of the
   free text in the body of a response.  Such a structured use of the
   symbol(s) allows recipient MUAs to correlate this reaction to the
   original message and possibly to display the information

   This facility defines a new MIME Content-Disposition, to be used in
   conjunction with the In-Reply-To header field, to specify that a part
   of a message containing one or more emojis be treated as a summary
   reaction to a previous message.

   Unless provided here, terminology, architecture and specification
   used in this document are incorporated from [Mail-Arch], [Mail-Fmt],
   [MIME], and [ABNF].  The ABNF rule Emoji-Seq is inherited from

   Discussion of this specification should take place on the ietf- mailing list.

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2.  Reaction Content-Disposition

   A message sent as a reply MAY include a part containing:

   Content-Disposition: Reaction

   If such a field is specified the content-type of the part MUST be:

   Content-Type: text/plain; charset=utf-8

   The content of this part is restricted to single line of emoji.  The
   [ABNF] is:

          part-content =  emoji *(lwsp emoji) CRLF

          emoji = emoji_sequence
          emoji_sequence = { defined in [Emoji-Seq] }

          base-emojis = thumbs-up / thumbs-down / grinning-face / frowning-face / crying-face

          thumbs-up = {U+1F44D}
          thumbs-down = {U+1F44E}
          grinning-face = {U+1F600}
          frowning-face = {U+2639}
          crying-face = {U+1F622}

   The rule emoji_sequence is inherited from [Emoji-Seq].  It permits
   one or more bytes to form a single presentation image.

   The emoji(s) express a recipient's summary reaction to the specific
   message referenced by the accompanying In-Reply-To header field.

   Reference to unallocated code points SHOULD NOT be treated as an
   error; associated bytes SHOULD be processed using the system default
   method for denoting an unallocated or undisplayable code point.

   The presentation aspects of reaction processing are necessarily MUA-
   specific and beyond the scope of this specification.  In terms of the
   message itself, recipient MUAs that support this mechanism operate as

   1.  If an In-Reply-To field is present check to see if it references
       a previous message the MUA has received.

   2.  If a reference to an existing message is found check for a part
       with a "reaction" content-disposition at either the outermost
       level or as part of a multipart at the outermost level.

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   3.  If such a part is found, and the content of the part conforms to
       the restrictions outlined above, remove the part from the message
       and process it as a reaction.

   4.  Processing terminates if no parts remain in the message.  If
       parts remain process the remaining message content as a reply.

   Again, the handling of a message that has been successfully processed
   is MUA-specific and beyond the scope of this specification.

3.  Usability Considerations

   This specification defines a mechanism for the structuring and
   carriage of information.  It does not define any user-level details
   of use.  However the design of the user-level mechanisms associated
   with this facility is paramount.  This section discusses some issues
   to consider.

   Creation:   Because an email environment is different from a typical
      social media platform, there are significant -- and potentially
      challenging -- choices in the design of the user interface, to
      support indication of a reaction.  Is the reaction to be sent only
      to the original author, or should it be sent to all recipients?
      Should the reaction always be sent in a discrete message
      containing only the reaction, or should the user also be able to
      include other message content?  (Note that carriage of the
      reaction in a normal email message enables inclusion of this other

   Display:  Reaction indications might be more useful when displayed in
      close visual proximity to the original message, rather than merely
      as part of an email response thread.

4.  Security Considerations

   This specification employs message content that is a strict subset of
   existing content, and thus introduces no new content-specific
   security considerations.

   This specification defines a distinct label for specialized message
   content.  Processing that handles the content differently from other
   content in the message body might introduce vulnerabilities.

5.  IANA Considerations

   New Content-Disposition Parameter Registrations

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   This document specifies a new "reaction" content disposition and its
   handling that should be added to the IANA registry.

6.  Normative References

   [ABNF]     Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 5234, January 2008.

              Davis, M., Ed. and P. Edberg., Ed., "Unicode(R) Technical
              Standard #51: Unicode Emoji", WEB
              September 2020.

              Crocker, D., "Internet Mail Architecture", RFC 5598, July

              Resnick, P., Ed., "Internet Message Format", RFC 5322,
              October 2008.

   [MIME]     Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

Appendix A.  Acknowledgements

   This specification has been discussed in the ietf-822 mailing list.
   Active commentary and suggestions were offered by: Nathaniel
   Borenstein, Richard Clayton, Ned Freed, Bron Gondwana, Valdis
   Klētnieks, John Levine, Brandon Long, Keith Moore, Pete Resnick,
   Michael Richardson, Alessandro Vesely

Authors' Addresses

   Dave Crocker
   Brandenburg InternetWorking


   Ricardo Signes


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   Ned Freed


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