Mailing Lists and Non-ASCII Addresses
RFC 6783

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Internet Engineering Task Force (IETF)                         J. Levine
Request for Comments: 6783                          Taughannock Networks
Obsoletes: 5983                                               R. Gellens
Category: Informational                            Qualcomm Incorporated
ISSN: 2070-1721                                            November 2012

                 Mailing Lists and Non-ASCII Addresses

Abstract

   This document describes considerations for mailing lists with the
   introduction of non-ASCII UTF-8 email addresses.  It outlines some
   possible scenarios for handling lists with mixtures of non-ASCII and
   traditional addresses but does not specify protocol changes or offer
   implementation or deployment advice.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see 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/rfc6783.

Copyright Notice

   Copyright (c) 2012 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Levine & Gellens              Informational                     [Page 1]
RFC 6783          Mailing Lists and Non-ASCII Addresses    November 2012

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
     1.1.  Mailing List Header Additions and Modifications . . . . . . 3
     1.2.  Non-ASCII Email Addresses . . . . . . . . . . . . . . . . . 3
   2.  Scenarios Involving Mailing Lists . . . . . . . . . . . . . . . 4
     2.1.  Fully SMTPUTF8 Lists  . . . . . . . . . . . . . . . . . . . 4
     2.2.  Mixed SMTPUTF8 and ASCII Lists  . . . . . . . . . . . . . . 5
     2.3.  SMTP Issues . . . . . . . . . . . . . . . . . . . . . . . . 5
   3.  List Headers  . . . . . . . . . . . . . . . . . . . . . . . . . 6
     3.1.  SMTPUTF8 List Headers . . . . . . . . . . . . . . . . . . . 6
     3.2.  Downgrading List Headers  . . . . . . . . . . . . . . . . . 7
     3.3.  Subscribers' Addresses in Downgraded Headers  . . . . . . . 8
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 8
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     5.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     5.2.  Informative References  . . . . . . . . . . . . . . . . . . 9

1.  Introduction

   This document describes considerations for mailing lists with the
   introduction of non-ASCII UTF-8 email addresses.  The usage of such
   addresses is described in [RFC6530].

   Mailing lists are an important part of email usage and collaborative
   communications.  The introduction of internationalized email
   addresses affects mailing lists in three main areas: (1) transport
   (receiving and sending messages); (2) message headers of received and
   retransmitted messages; and (3) mailing list operational policies.

   A mailing list is a mechanism that distributes a message to multiple
   recipients when the originator sends it to a single address.  An
   agent, usually software rather than a person, at that single address
   receives the message and then causes the message to be redistributed
   to a list of recipients.  This agent usually sets the envelope return
   address (henceforth called the "bounce address") of the redistributed
   message to a different address from that of the original message.
   Using a different bounce address directs error and other
   automatically generated messages to an error-handling address
   associated with the mailing list.  This sends error and other
   automatic messages to the list agent, which can often do something
   useful with them, rather than to the original sender, who typically
   doesn't control the list and hence can't do anything about them.

   In most cases, the mailing list agent redistributes a received
   message to its subscribers as a new message, that is, conceptually it