



Structured Email                                                  P. Tao
Internet-Draft                                                Apple Inc.
Intended status: Standards Track                            2 March 2026
Expires: 3 September 2026


                       Structured Quoted Content
               draft-tao-sml-structured-quoted-content-00

Abstract

   This document describes a machine-readable format for conveying
   quoted content in email messages.  This can be used when replying to
   or forwarding an email message.

   Structured quoted content is expected to be used in conjunction with
   conventional, human-readable quote formatting.  They are based on the
   forthcoming "structured email" specification defined in [I-D.ietf-
   sml-structured-email-03] and related drafts.

About This Document

   This note is to be removed before publishing as an RFC.

   The latest revision of this draft can be found at
   https://ptao.github.io/id-structured-quoted-content/draft-tao-sml-
   structured-quoted-content.html.  Status information for this document
   may be found at https://datatracker.ietf.org/doc/draft-tao-sml-
   structured-quoted-content/.

   Discussion of this document takes place on the Structured Email
   Working Group mailing list (mailto:sml@ietf.org), which is archived
   at https://mailarchive.ietf.org/arch/browse/sml/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/sml/.

   Source for this draft and an issue tracker can be found at
   https://github.com/ptao/id-structured-quoted-content.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.




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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 3 September 2026.

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   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Structured Email Format . . . . . . . . . . . . . . . . . . .   3
     3.1.  Structured Data Type  . . . . . . . . . . . . . . . . . .   3
     3.2.  Vocabularies  . . . . . . . . . . . . . . . . . . . . . .   4
   4.  JSON-LD Objects . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  HTML Format . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Plaintext Format  . . . . . . . . . . . . . . . . . . . . . .   5
   7.  Backwards Compatibility . . . . . . . . . . . . . . . . . . .   5
   8.  MUA Guidance  . . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   11. Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Email messages often content quoted sections of earlier email
   messages, typically as part of a reply or a forwarded message.  The
   presentation is entirely determined by the sending MUA.  Though
   various conventions have evolved around this quoting, the behavior is
   still largely unstandardized, and behavior differs widely between
   MUAs.




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   Some notable differences include:

   *  Where newly authored content may be inserted relative to the
      quoted content.

      -  Some MUAs allow inserting new content only above the quoted
         message, while some allow inserting new content inline between
         blocks of quoted text.

   *  The formatting used, whether HTML or plaintext, to denote the
      quoted section.

   *  Whether some set of headers are also quoted, or whether an
      attribution line or preamble is inserted.

      -  Whether the headers, attribution line, or preamble are
         localized into the sender's device language.

   *  Whether attachments are included in the quoted content.

   Due to the above, an email chain in a user's inbox may involve a wide
   mix of differing quoting styles, which can be visually disorienting.

   The goal of this draft is to introduce a standardized way to
   structure quoted content in message replies and forwarded messages.
   This allows the sending MUA to annotate the various components of the
   quoted content in such a way that the receiving MUA can then apply a
   consistent presentation across all messages.

2.  Conventions and Definitions

   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.

3.  Structured Email Format

3.1.  Structured Data Type

   All quoted content will be transmitted as "Partial representation" as
   defined by https://datatracker.ietf.org/doc/html/draft-ietf-sml-
   structured-email-05#name-partial-representation.







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3.2.  Vocabularies

   Structured Quoted Content uses the SchemaOrg vocabulary, as well as a
   custom vocabulary to be defined at *INSERT LINK*.

4.  JSON-LD Objects

   Structured Quoted Content uses the following object types.

   *EmailMessage*

* vocabulary: schema.org and sml.draft.iana.org
* id format: "mid:<message-id header>"
* The following properties can be set: sender, toRecipient, dateSent, dateReceived, about (subject)
    * Each property should have its own id

   *QuotedContent*

   * vocabulary: sml.draft.iana.org
   * id format: "quoted-content:<UUID>"
   * Properties:
       * message
           * References EmailMessage which this item is quoting
       * headerBlock
           * References QuotedHeaderBlock
           * optional
       * attribution
           * References QuoteAttribution
           * optional
       * content
           * References one or more TextContent or QuotedContent

   *QuotedHeaderBlock*

   * vocabulary: sml.draft.iana.org
   * id format: "quoted-header-block:<UUID>"
   * Properties:
       * header
           * References one or more QuotedHeader

   *QuotedHeader*










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   * vocabulary: sml.draft.iana.org
   * id format: "quoted-header:<UUID>"
   * Properties:
       * label
           * Text label for the header
       * value
           * References one of the properties of an EmailMessage

   *QuoteAttribution*

* vocabulary: sml.draft.iana.org
* id format: "quote-attribution:<UUID>"
* Properties:
    * date
        * References either the dateSent or dateReceived property of an EmailMessage
    * from
        * References the sender property of an Emailmessage

   *TextContent*

   * vocabulary: sml.draft.iana.org
   * id format: "text-content:<UUID>"
   * Properties:

   Note, TextContent has no properties.

   TODO: There should be a type for a preamble for forwarding.

5.  HTML Format

   Each quoted block will be wrapped in an HTML element (typically div
   or span) with a data-source-id and a data-id property.  The data-
   source-id is a cid: URI referencing the MIME part which contains the
   structured data definitions.  The data-id is the id of the matching
   element.

6.  Plaintext Format

   TODO Plaintext

7.  Backwards Compatibility

   In a long reply chain, not all MUAs involved may be SML-aware.  This
   results in two types of mixed content: 1.  A MUA which is compliant
   with Structured Quoted Content quoting a message which does not have
   Structured Quoted Content. 1.  A MUA which is not aware of Structured
   Quoted Content quoting a message which has Structured Quoted Content.




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   In the first case, the MUA SHOULD NOT try to retroactively determine
   the quoted content structure of the email it is quoting.  In other
   words, it SHOULD NOT attempt to parse the HTML or plain-text
   formatting of that message in order to build a structured
   representation.  Instead, any structured quoted content that it
   generates should treat the quoted message as one having no quoted
   content itself.

   The MUA in the second situation is by definition not bound to any
   behavior specified in this draft.  It may likely do one or both of
   the following: 1.  Modify the HTML or plaintext in such a way that
   the existing structured content properties no longer behave as
   expected. 2.  Modify the MIME structure in such a way that the
   structured quoted content is no longer valid.  For example it may: *
   Change the MIME structure in such a way that the message is no longer
   classified as a "partial representation".  * Remove or modify the
   application/ld+json part.

   In general, it can be assumed that for a message which contains
   Structured Quoted Content, the Structured Quoted Content represents
   the most recent contiguous set of messages.  This set of messages may
   be a subset of all the messages which actually comprise the quoted
   reply chain.  Such a case occurs when the oldest message represented
   in the Structured Quoted Content has quoted a message sent by a MUA
   which was not aware of Structured Quoted Content.

   When rendering such a message, only the first contiguous set of
   Structured Quoted Content should be treated as Structured Quoted
   Content.  Any HTML or JSON-LD is found which hints at the presence of
   Structured Quoted Content further back in the reply chain, but which
   has not made it to the receiving MUA intact, should be ignored and
   that portion of HTML should be rendered as not containing Structured
   Quoted Content.

8.  MUA Guidance

   TODO: List potential usages/purposes/benefits

   Some examples:

   *  More reliable quoted content parsing/recognition by all compliant
      MUAs

   *  Allow for consistent and localized quoting style (determined by
      receiver rather than sender)

   *  Better condensed display




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   *  Clearer attribution of deeply nested content

   *  Clearer attribution for inline quoting

9.  Security Considerations

   TODO Security

10.  IANA Considerations

   This document has no IANA actions.

11.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [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/rfc/rfc8174>.

Acknowledgments

   TODO acknowledge.

Author's Address

   Phillip Tao
   Apple Inc.
   Email: ptao@apple.com



















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