Update to Internet Message Format to Allow Group Syntax in the "From:" and "Sender:" Header Fields
RFC 6854

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Internet Engineering Task Force (IETF)                          B. Leiba
Request for Comments: 6854                           Huawei Technologies
Updates: 5322                                                 March 2013
Category: Standards Track
ISSN: 2070-1721

       Update to Internet Message Format to Allow Group Syntax in
                the "From:" and "Sender:" Header Fields

Abstract

   The Internet Message Format (RFC 5322) allows "group" syntax in some
   email header fields, such as "To:" and "CC:", but not in "From:" or
   "Sender:".  This document updates RFC 5322 to relax that restriction,
   allowing group syntax in those latter fields, as well as in
   "Resent-From:" and "Resent-Sender:", in certain situations.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6854.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Leiba                        Standards Track                    [Page 1]
RFC 6854          Group Syntax in "From:" and "Sender:"       March 2013

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . . . 3
       1.1.1.  Requirements Notation . . . . . . . . . . . . . . . . . 3
       1.1.2.  Syntactic Notation  . . . . . . . . . . . . . . . . . . 3
   2.  Allowing Group Syntax in "From:" and "Sender:"  . . . . . . . . 3
     2.1.  Replacement of RFC 5322, Section 3.6.2. Originator Fields . 4
     2.2.  Update to RFC 5322, Section 3.6.6. Resent Fields  . . . . . 5
   3.  Applicability Statement . . . . . . . . . . . . . . . . . . . . 6
   4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 9
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 9
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 9

1.  Introduction

   The Internet Message Format, as far back as RFC 822 [RFC0822], has
   always required a usable address to appear in the "From:" header
   field of messages in order to allow replies to be sent.  To this end,
   the syntax of messages, up to and including the current specification
   [RFC5322], has required the use of the mailbox address form in the
   originator ("From:" and "Sender:") fields of messages and has
   specifically forbidden the use of the group address form, which
   permits an empty list of addresses (that is, an address list with no
   address included that might be used for a reply).

   However, the use cases for the "From:" field have evolved.  There are
   numerous instances of automated systems that wish to send email but
   cannot handle replies, and a "From:" field with no usable addresses
   would be extremely useful for that purpose.  More recently, work with
   internationalized email addresses [RFC6530] creates a real need to
   take a message with an internationalized email address and hand it to
   an older client that would have no ability to reply to such an
   address but might still wish to display the contents of the message.
   The group construct provides an existing syntax for unusable
   addresses (using the empty list of addresses) and also allows for a
   text label that describes the originator.  For example:

      From: Automated System:;

   A review of many current email programs finds that all reviewed
   clients will properly display a message with group syntax in the
   "From:" field.  At worst, such programs generate an error message
   when an attempt is made to reply to such a message.  No other
   interoperability problems have been discovered.

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