DNSWL Email Authentication Method Extension
draft-vesely-authmethod-dnswl-13

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Last updated 2020-01-12 (latest revision 2019-12-20)
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IETF                                                           A. Vesely
Internet-Draft                                         December 20, 2019
Intended status: Informational
Expires: June 22, 2020

              DNSWL Email Authentication Method Extension
                    draft-vesely-authmethod-dnswl-13

Abstract

   This document describes an additional Email Authentication Method
   compliant with RFC 8601.  The method consists in looking up the
   sender's IP address in a DNS whitelist.  This document is provided
   for information in case the method is seen in the field, as well as
   to suggest a useful practice and register the relevant keywords.

   This document does not consider black lists.

Status of This Memo

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

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   This Internet-Draft will expire on June 22, 2020.

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
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   (http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Method Details  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  TXT Record Contents . . . . . . . . . . . . . . . . . . . . .   5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Email Authentication Methods  . . . . . . . . . . . . . .   6
     4.2.  Email Authentication Property Type  . . . . . . . . . . .   6
     4.3.  Email Authentication Result Names . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
     5.1.  Over Quota Signaling  . . . . . . . . . . . . . . . . . .   7
     5.2.  Security of DNSSEC Validation . . . . . . . . . . . . . .   7
     5.3.  Inherited Security Considerations . . . . . . . . . . . .   8
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Appendix A.  Example  . . . . . . . . . . . . . . . . . . . . . .  10
   Appendix B.  Known Implementation . . . . . . . . . . . . . . . .  11
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   One of the many checks that mail servers carry out is to query domain
   name system whitelists (DNSWL).  That method is fully discussed in
   [RFC5782].  The DNS [RFC1034] lookup is based on the connecting
   client's IP address, IPv4 or IPv6, and returns zero or more A
   records.  The latter are IPv4 IP addresses in the range 127/8.
   Depending on the query, TXT records with varying content can also be
   retrieved.  Query examples are given in Appendix A.

   Since the IP address is known as soon as the connection is accepted,
   this check can occur very early in an SMTP transaction.  Its result
   can be used to counterweight policies that typically occur at early
   stages too, such as the Sender Policy Framework (SPF, the last
   paragraph of Appendix D.3 of [RFC7208] is also illustrated in
   Appendix A).  In addition, the result of a DNSWL lookup can also be
   used at later stages; for example, a delivery agent can use it to
   learn the trustworthiness of a mail relay in order to estimate the
   spamminess of an email message.  The latter possibility needs a place
   to collect query results for downstream use, which is precisely what
   the Authentication-Results header field aims at providing.

   Results often contain additional data, encoded according to DNSWL-
   specific criteria.  The method described in this document considers
   only whitelists --one of the major branches described by [RFC5782].
   There are also black/block lists, DNSBL, and combined lists.  Since
   they all have the same structure, the abbreviation DNSxL is used to
   mean any.  Now, the core procedures of a mail transfer agent (MTA)

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