Email Authentication for Internationalized Mail
RFC 8616

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Internet Engineering Task Force (IETF)                         J. Levine
Request for Comments: 8616                          Taughannock Networks
Updates: 6376, 7208, 7489                                      June 2019
Category: Standards Track
ISSN: 2070-1721

            Email Authentication for Internationalized Mail

Abstract

   Sender Policy Framework (SPF) (RFC 7208), DomainKeys Identified Mail
   (DKIM) (RFC 6376), and Domain-based Message Authentication,
   Reporting, and Conformance (DMARC) (RFC 7489) enable a domain owner
   to publish email authentication and policy information in the DNS.
   In internationalized email, domain names can occur both as U-labels
   and A-labels.  This specification updates the SPF, DKIM, and DMARC
   specifications to clarify which form of internationalized domain
   names to use in those specifications.

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 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8616.

Copyright Notice

   Copyright (c) 2019 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
   (https://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.

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RFC 8616                   EAI Authentication                  June 2019

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  General Principles  . . . . . . . . . . . . . . . . . . . . .   3
   4.  SPF and Internationalized Mail  . . . . . . . . . . . . . . .   3
   5.  DKIM and Internationalized Mail . . . . . . . . . . . . . . .   3
   6.  DMARC and Internationalized Mail  . . . . . . . . . . . . . .   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   SPF [RFC7208], DKIM [RFC6376], and DMARC [RFC7489] enable a domain
   owner to publish email authentication and policy information in the
   DNS.  SPF primarily publishes information about what host addresses
   are authorized to send mail for a domain.  DKIM places cryptographic
   signatures on email messages, with the validation keys published in
   the DNS.  DMARC publishes policy information related to the domain in
   the From: header field of email messages.

   In conventional email, all domain names are ASCII in all contexts, so
   there is no question about the representation of the domain names.
   All internationalized domain names are represented as A-labels
   [RFC5890] in message header fields, SMTP sessions, and the DNS.

   Internationalized mail [RFC6530] (generally called "EAI" for Email
   Address Internationalization) allows U-labels in SMTP sessions
   [RFC6531] and message header fields [RFC6532].

   Every U-label is equivalent to an A-label, so in principle, the
   choice of label format will not cause ambiguities.  But in practice,
   consistent use of label formats will make it more likely that code
   for mail senders and receivers interoperates.

   Internationalized mail also allows UTF-8-encoded Unicode characters
   in the local parts of mailbox names, which were historically only
   ASCII.

2.  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.

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RFC 8616                   EAI Authentication                  June 2019

   The term "IDN", for Internationalized Domain Name, refers to a domain
   name containing either U-labels or A-labels.