File: rfc8904.html

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<!DOCTYPE html>
<html lang="en" class="RFC">
<head>
<meta charset="utf-8">
<meta content="Common,Latin" name="scripts">
<meta content="initial-scale=1.0" name="viewport">
<title>RFC 8904: DNS Whitelist (DNSWL) Email Authentication Method Extension</title>
<meta content="Alessandro Vesely" name="author">
<meta content="
       
This document describes an email authentication method compliant
with RFC 8601.  The method consists of looking up the sender's IP address in a
DNS whitelist.  This document provides information in case the method is seen
in the field, suggests a useful practice, and registers the
relevant keywords.
       
       
 This document does not consider blacklists.
       
    " name="description">
<meta content="xml2rfc 3.1.1" name="generator">
<meta content="DNSWL" name="keyword">
<meta content="EMAIL" name="keyword">
<meta content="Authentication-Results" name="keyword">
<meta content="8904" name="rfc.number">
<link href="rfc8904.xml" rel="alternate" type="application/rfc+xml">
<link href="#copyright" rel="license">
<style type="text/css">/*

  NOTE: Changes at the bottom of this file overrides some earlier settings.

  Once the style has stabilized and has been adopted as an official RFC style,
  this can be consolidated so that style settings occur only in one place, but
  for now the contents of this file consists first of the initial CSS work as
  provided to the RFC Formatter (xml2rfc) work, followed by itemized and
  commented changes found necssary during the development of the v3
  formatters.

*/

/* fonts */
@import url('https://fonts.googleapis.com/css?family=Noto+Sans'); /* Sans-serif */
@import url('https://fonts.googleapis.com/css?family=Noto+Serif'); /* Serif (print) */
@import url('https://fonts.googleapis.com/css?family=Roboto+Mono'); /* Monospace */

@viewport {
  zoom: 1.0;
  width: extend-to-zoom;
}
@-ms-viewport {
  width: extend-to-zoom;
  zoom: 1.0;
}
/* general and mobile first */
html {
}
body {
  max-width: 90%;
  margin: 1.5em auto;
  color: #222;
  background-color: #fff;
  font-size: 14px;
  font-family: 'Noto Sans', Arial, Helvetica, sans-serif;
  line-height: 1.6;
  scroll-behavior: smooth;
}
.ears {
  display: none;
}

/* headings */
#title, h1, h2, h3, h4, h5, h6 {
  margin: 1em 0 0.5em;
  font-weight: bold;
  line-height: 1.3;
}
#title {
  clear: both;
  border-bottom: 1px solid #ddd;
  margin: 0 0 0.5em 0;
  padding: 1em 0 0.5em;
}
.author {
  padding-bottom: 4px;
}
h1 {
  font-size: 26px;
  margin: 1em 0;
}
h2 {
  font-size: 22px;
  margin-top: -20px;  /* provide offset for in-page anchors */
  padding-top: 33px;
}
h3 {
  font-size: 18px;
  margin-top: -36px;  /* provide offset for in-page anchors */
  padding-top: 42px;
}
h4 {
  font-size: 16px;
  margin-top: -36px;  /* provide offset for in-page anchors */
  padding-top: 42px;
}
h5, h6 {
  font-size: 14px;
}
#n-copyright-notice {
  border-bottom: 1px solid #ddd;
  padding-bottom: 1em;
  margin-bottom: 1em;
}
/* general structure */
p {
  padding: 0;
  margin: 0 0 1em 0;
  text-align: left;
}
div, span {
  position: relative;
}
div {
  margin: 0;
}
.alignRight.art-text {
  background-color: #f9f9f9;
  border: 1px solid #eee;
  border-radius: 3px;
  padding: 1em 1em 0;
  margin-bottom: 1.5em;
}
.alignRight.art-text pre {
  padding: 0;
}
.alignRight {
  margin: 1em 0;
}
.alignRight > *:first-child {
  border: none;
  margin: 0;
  float: right;
  clear: both;
}
.alignRight > *:nth-child(2) {
  clear: both;
  display: block;
  border: none;
}
svg {
  display: block;
}
.alignCenter.art-text {
  background-color: #f9f9f9;
  border: 1px solid #eee;
  border-radius: 3px;
  padding: 1em 1em 0;
  margin-bottom: 1.5em;
}
.alignCenter.art-text pre {
  padding: 0;
}
.alignCenter {
  margin: 1em 0;
}
.alignCenter > *:first-child {
  border: none;
  /* this isn't optimal, but it's an existence proof.  PrinceXML doesn't
     support flexbox yet.
  */
  display: table;
  margin: 0 auto;
}

/* lists */
ol, ul {
  padding: 0;
  margin: 0 0 1em 2em;
}
ol ol, ul ul, ol ul, ul ol {
  margin-left: 1em;
}
li {
  margin: 0 0 0.25em 0;
}
.ulCompact li {
  margin: 0;
}
ul.empty, .ulEmpty {
  list-style-type: none;
}
ul.empty li, .ulEmpty li {
  margin-top: 0.5em;
}
ul.compact, .ulCompact,
ol.compact, .olCompact {
  line-height: 100%;
  margin: 0 0 0 2em;
}

/* definition lists */
dl {
}
dl > dt {
  float: left;
  margin-right: 1em;
}
/* 
dl.nohang > dt {
  float: none;
}
*/
dl > dd {
  margin-bottom: .8em;
  min-height: 1.3em;
}
dl.compact > dd, .dlCompact > dd {
  margin-bottom: 0em;
}
dl > dd > dl {
  margin-top: 0.5em;
  margin-bottom: 0em;
}

/* links */
a {
  text-decoration: none;
}
a[href] {
  color: #22e; /* Arlen: WCAG 2019 */
}
a[href]:hover {
  background-color: #f2f2f2;
}
figcaption a[href],
a[href].selfRef {
  color: #222;
}
/* XXX probably not this:
a.selfRef:hover {
  background-color: transparent;
  cursor: default;
} */

/* Figures */
tt, code, pre, code {
  background-color: #f9f9f9;
  font-family: 'Roboto Mono', monospace;
}
pre {
  border: 1px solid #eee;
  margin: 0;
  padding: 1em;
}
img {
  max-width: 100%;
}
figure {
  margin: 0;
}
figure blockquote {
  margin: 0.8em 0.4em 0.4em;
}
figcaption {
  font-style: italic;
  margin: 0 0 1em 0;
}
@media screen {
  pre {
    overflow-x: auto;
    max-width: 100%;
    max-width: calc(100% - 22px);
  }
}

/* aside, blockquote */
aside, blockquote {
  margin-left: 0;
  padding: 1.2em 2em;
}
blockquote {
  background-color: #f9f9f9;
  color: #111; /* Arlen: WCAG 2019 */
  border: 1px solid #ddd;
  border-radius: 3px;
  margin: 1em 0;
}
cite {
  display: block;
  text-align: right;
  font-style: italic;
}

/* tables */
table {
  width: 100%;
  margin: 0 0 1em;
  border-collapse: collapse;
  border: 1px solid #eee;
}
th, td {
  text-align: left;
  vertical-align: top;
  padding: 0.5em 0.75em;
}
th {
  text-align: left;
  background-color: #e9e9e9;
}
tr:nth-child(2n+1) > td {
  background-color: #f5f5f5;
}
table caption {
  font-style: italic;
  margin: 0;
  padding: 0;
  text-align: left;
}
table p {
  /* XXX to avoid bottom margin on table row signifiers. If paragraphs should
     be allowed within tables more generally, it would be far better to select on a class. */
  margin: 0;
}

/* pilcrow */
a.pilcrow {
  color: #666; /* Arlen: AHDJ 2019 */
  text-decoration: none;
  visibility: hidden;
  user-select: none;
  -ms-user-select: none;
  -o-user-select:none;
  -moz-user-select: none;
  -khtml-user-select: none;
  -webkit-user-select: none;
  -webkit-touch-callout: none;
}
@media screen {
  aside:hover > a.pilcrow,
  p:hover > a.pilcrow,
  blockquote:hover > a.pilcrow,
  div:hover > a.pilcrow,
  li:hover > a.pilcrow,
  pre:hover > a.pilcrow {
    visibility: visible;
  }
  a.pilcrow:hover {
    background-color: transparent;
  }
}

/* misc */
hr {
  border: 0;
  border-top: 1px solid #eee;
}
.bcp14 {
  font-variant: small-caps;
}

.role {
  font-variant: all-small-caps;
}

/* info block */
#identifiers {
  margin: 0;
  font-size: 0.9em;
}
#identifiers dt {
  width: 3em;
  clear: left;
}
#identifiers dd {
  float: left;
  margin-bottom: 0;
}
#identifiers .authors .author {
  display: inline-block;
  margin-right: 1.5em;
}
#identifiers .authors .org {
  font-style: italic;
}

/* The prepared/rendered info at the very bottom of the page */
.docInfo {
  color: #666; /* Arlen: WCAG 2019 */
  font-size: 0.9em;
  font-style: italic;
  margin-top: 2em;
}
.docInfo .prepared {
  float: left;
}
.docInfo .prepared {
  float: right;
}

/* table of contents */
#toc  {
  padding: 0.75em 0 2em 0;
  margin-bottom: 1em;
}
nav.toc ul {
  margin: 0 0.5em 0 0;
  padding: 0;
  list-style: none;
}
nav.toc li {
  line-height: 1.3em;
  margin: 0.75em 0;
  padding-left: 1.2em;
  text-indent: -1.2em;
}
/* references */
.references dt {
  text-align: right;
  font-weight: bold;
  min-width: 7em;
}
.references dd {
  margin-left: 8em;
  overflow: auto;
}

.refInstance {
  margin-bottom: 1.25em;
}

.references .ascii {
  margin-bottom: 0.25em;
}

/* index */
.index ul {
  margin: 0 0 0 1em;
  padding: 0;
  list-style: none;
}
.index ul ul {
  margin: 0;
}
.index li {
  margin: 0;
  text-indent: -2em;
  padding-left: 2em;
  padding-bottom: 5px;
}
.indexIndex {
  margin: 0.5em 0 1em;
}
.index a {
  font-weight: 700;
}
/* make the index two-column on all but the smallest screens */
@media (min-width: 600px) {
  .index ul {
    -moz-column-count: 2;
    -moz-column-gap: 20px;
  }
  .index ul ul {
    -moz-column-count: 1;
    -moz-column-gap: 0;
  }
}

/* authors */
address.vcard {
  font-style: normal;
  margin: 1em 0;
}

address.vcard .nameRole {
  font-weight: 700;
  margin-left: 0;
}
address.vcard .label {
  font-family: "Noto Sans",Arial,Helvetica,sans-serif;
  margin: 0.5em 0;
}
address.vcard .type {
  display: none;
}
.alternative-contact {
  margin: 1.5em 0 1em;
}
hr.addr {
  border-top: 1px dashed;
  margin: 0;
  color: #ddd;
  max-width: calc(100% - 16px);
}

/* temporary notes */
.rfcEditorRemove::before {
  position: absolute;
  top: 0.2em;
  right: 0.2em;
  padding: 0.2em;
  content: "The RFC Editor will remove this note";
  color: #9e2a00; /* Arlen: WCAG 2019 */
  background-color: #ffd; /* Arlen: WCAG 2019 */
}
.rfcEditorRemove {
  position: relative;
  padding-top: 1.8em;
  background-color: #ffd; /* Arlen: WCAG 2019 */
  border-radius: 3px;
}
.cref {
  background-color: #ffd; /* Arlen: WCAG 2019 */
  padding: 2px 4px;
}
.crefSource {
  font-style: italic;
}
/* alternative layout for smaller screens */
@media screen and (max-width: 1023px) {
  body {
    padding-top: 2em;
  }
  #title {
    padding: 1em 0;
  }
  h1 {
    font-size: 24px;
  }
  h2 {
    font-size: 20px;
    margin-top: -18px;  /* provide offset for in-page anchors */
    padding-top: 38px;
  }
  #identifiers dd {
    max-width: 60%;
  }
  #toc {
    position: fixed;
    z-index: 2;
    top: 0;
    right: 0;
    padding: 0;
    margin: 0;
    background-color: inherit;
    border-bottom: 1px solid #ccc;
  }
  #toc h2 {
    margin: -1px 0 0 0;
    padding: 4px 0 4px 6px;
    padding-right: 1em;
    min-width: 190px;
    font-size: 1.1em;
    text-align: right;
    background-color: #444;
    color: white;
    cursor: pointer;
  }
  #toc h2::before { /* css hamburger */
    float: right;
    position: relative;
    width: 1em;
    height: 1px;
    left: -164px;
    margin: 6px 0 0 0;
    background: white none repeat scroll 0 0;
    box-shadow: 0 4px 0 0 white, 0 8px 0 0 white;
    content: "";
  }
  #toc nav {
    display: none;
    padding: 0.5em 1em 1em;
    overflow: auto;
    height: calc(100vh - 48px);
    border-left: 1px solid #ddd;
  }
}

/* alternative layout for wide screens */
@media screen and (min-width: 1024px) {
  body {
    max-width: 724px;
    margin: 42px auto;
    padding-left: 1.5em;
    padding-right: 29em;
  }
  #toc {
    position: fixed;
    top: 42px;
    right: 42px;
    width: 25%;
    margin: 0;
    padding: 0 1em;
    z-index: 1;
  }
  #toc h2 {
    border-top: none;
    border-bottom: 1px solid #ddd;
    font-size: 1em;
    font-weight: normal;
    margin: 0;
    padding: 0.25em 1em 1em 0;
  }
  #toc nav {
    display: block;
    height: calc(90vh - 84px);
    bottom: 0;
    padding: 0.5em 0 0;
    overflow: auto;
  }
  img { /* future proofing */
    max-width: 100%;
    height: auto;
  }
}

/* pagination */
@media print {
  body {

    width: 100%;
  }
  p {
    orphans: 3;
    widows: 3;
  }
  #n-copyright-notice {
    border-bottom: none;
  }
  #toc, #n-introduction {
    page-break-before: always;
  }
  #toc {
    border-top: none;
    padding-top: 0;
  }
  figure, pre {
    page-break-inside: avoid;
  }
  figure {
    overflow: scroll;
  }
  h1, h2, h3, h4, h5, h6 {
    page-break-after: avoid;
  }
  h2+*, h3+*, h4+*, h5+*, h6+* {
    page-break-before: avoid;
  }
  pre {
    white-space: pre-wrap;
    word-wrap: break-word;
    font-size: 10pt;
  }
  table {
    border: 1px solid #ddd;
  }
  td {
    border-top: 1px solid #ddd;
  }
}

/* This is commented out here, as the string-set: doesn't
   pass W3C validation currently */
/*
.ears thead .left {
  string-set: ears-top-left content();
}

.ears thead .center {
  string-set: ears-top-center content();
}

.ears thead .right {
  string-set: ears-top-right content();
}

.ears tfoot .left {
  string-set: ears-bottom-left content();
}

.ears tfoot .center {
  string-set: ears-bottom-center content();
}

.ears tfoot .right {
  string-set: ears-bottom-right content();
}
*/

@page :first {
  padding-top: 0;
  @top-left {
    content: normal;
    border: none;
  }
  @top-center {
    content: normal;
    border: none;
  }
  @top-right {
    content: normal;
    border: none;
  }
}

@page {
  size: A4;
  margin-bottom: 45mm;
  padding-top: 20px;
  /* The follwing is commented out here, but set appropriately by in code, as
     the content depends on the document */
  /*
  @top-left {
    content: 'Internet-Draft';
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-left {
    content: string(ears-top-left);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-center {
    content: string(ears-top-center);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-right {
    content: string(ears-top-right);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @bottom-left {
    content: string(ears-bottom-left);
    vertical-align: top;
    border-top: solid 1px #ccc;
  }
  @bottom-center {
    content: string(ears-bottom-center);
    vertical-align: top;
    border-top: solid 1px #ccc;
  }
  @bottom-right {
      content: '[Page ' counter(page) ']';
      vertical-align: top;
      border-top: solid 1px #ccc;
  }
  */

}

/* Changes introduced to fix issues found during implementation */
/* Make sure links are clickable even if overlapped by following H* */
a {
  z-index: 2;
}
/* Separate body from document info even without intervening H1 */
section {
  clear: both;
}


/* Top align author divs, to avoid names without organization dropping level with org names */
.author {
  vertical-align: top;
}

/* Leave room in document info to show Internet-Draft on one line */
#identifiers dt {
  width: 8em;
}

/* Don't waste quite as much whitespace between label and value in doc info */
#identifiers dd {
  margin-left: 1em;
}

/* Give floating toc a background color (needed when it's a div inside section */
#toc {
  background-color: white;
}

/* Make the collapsed ToC header render white on gray also when it's a link */
@media screen and (max-width: 1023px) {
  #toc h2 a,
  #toc h2 a:link,
  #toc h2 a:focus,
  #toc h2 a:hover,
  #toc a.toplink,
  #toc a.toplink:hover {
    color: white;
    background-color: #444;
    text-decoration: none;
  }
}

/* Give the bottom of the ToC some whitespace */
@media screen and (min-width: 1024px) {
  #toc {
    padding: 0 0 1em 1em;
  }
}

/* Style section numbers with more space between number and title */
.section-number {
  padding-right: 0.5em;
}

/* prevent monospace from becoming overly large */
tt, code, pre, code {
  font-size: 95%;
}

/* Fix the height/width aspect for ascii art*/
pre.sourcecode,
.art-text pre {
  line-height: 1.12;
}


/* Add styling for a link in the ToC that points to the top of the document */
a.toplink {
  float: right;
  margin-right: 0.5em;
}

/* Fix the dl styling to match the RFC 7992 attributes */
dl > dt,
dl.dlParallel > dt {
  float: left;
  margin-right: 1em;
}
dl.dlNewline > dt {
  float: none;
}

/* Provide styling for table cell text alignment */
table td.text-left,
table th.text-left {
  text-align: left;
}
table td.text-center,
table th.text-center {
  text-align: center;
}
table td.text-right,
table th.text-right {
  text-align: right;
}

/* Make the alternative author contact informatio look less like just another
   author, and group it closer with the primary author contact information */
.alternative-contact {
  margin: 0.5em 0 0.25em 0;
}
address .non-ascii {
  margin: 0 0 0 2em;
}

/* With it being possible to set tables with alignment
  left, center, and right, { width: 100%; } does not make sense */
table {
  width: auto;
}

/* Avoid reference text that sits in a block with very wide left margin,
   because of a long floating dt label.*/
.references dd {
  overflow: visible;
}

/* Control caption placement */
caption {
  caption-side: bottom;
}

/* Limit the width of the author address vcard, so names in right-to-left
   script don't end up on the other side of the page. */

address.vcard {
  max-width: 30em;
  margin-right: auto;
}

/* For address alignment dependent on LTR or RTL scripts */
address div.left {
  text-align: left;
}
address div.right {
  text-align: right;
}

/* Provide table alignment support.  We can't use the alignX classes above
   since they do unwanted things with caption and other styling. */
table.right {
 margin-left: auto;
 margin-right: 0;
}
table.center {
 margin-left: auto;
 margin-right: auto;
}
table.left {
 margin-left: 0;
 margin-right: auto;
}

/* Give the table caption label the same styling as the figcaption */
caption a[href] {
  color: #222;
}

@media print {
  .toplink {
    display: none;
  }

  /* avoid overwriting the top border line with the ToC header */
  #toc {
    padding-top: 1px;
  }

  /* Avoid page breaks inside dl and author address entries */
  .vcard {
    page-break-inside: avoid;
  }

}
/* Tweak the bcp14 keyword presentation */
.bcp14 {
  font-variant: small-caps;
  font-weight: bold;
  font-size: 0.9em;
}
/* Tweak the invisible space above H* in order not to overlay links in text above */
 h2 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 31px;
 }
 h3 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
 h4 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
/* Float artwork pilcrow to the right */
@media screen {
  .artwork a.pilcrow {
    display: block;
    line-height: 0.7;
    margin-top: 0.15em;
  }
}
/* Make pilcrows on dd visible */
@media screen {
  dd:hover > a.pilcrow {
    visibility: visible;
  }
}
/* Make the placement of figcaption match that of a table's caption
   by removing the figure's added bottom margin */
.alignLeft.art-text,
.alignCenter.art-text,
.alignRight.art-text {
   margin-bottom: 0;
}
.alignLeft,
.alignCenter,
.alignRight {
  margin: 1em 0 0 0;
}
/* In print, the pilcrow won't show on hover, so prevent it from taking up space,
   possibly even requiring a new line */
@media print {
  a.pilcrow {
    display: none;
  }
}
/* Styling for the external metadata */
div#external-metadata {
  background-color: #eee;
  padding: 0.5em;
  margin-bottom: 0.5em;
  display: none;
}
div#internal-metadata {
  padding: 0.5em;                       /* to match the external-metadata padding */
}
/* Styling for title RFC Number */
h1#rfcnum {
  clear: both;
  margin: 0 0 -1em;
  padding: 1em 0 0 0;
}
/* Make .olPercent look the same as <ol><li> */
dl.olPercent > dd {
  margin-bottom: 0.25em;
  min-height: initial;
}
/* Give aside some styling to set it apart */
aside {
  border-left: 1px solid #ddd;
  margin: 1em 0 1em 2em;
  padding: 0.2em 2em;
}
aside > dl,
aside > ol,
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<table class="ears">
<thead><tr>
<td class="left">RFC 8904</td>
<td class="center">DNSWL Email Auth Method Extension</td>
<td class="right">September 2020</td>
</tr></thead>
<tfoot><tr>
<td class="left">Vesely</td>
<td class="center">Informational</td>
<td class="right">[Page]</td>
</tr></tfoot>
</table>
<div id="external-metadata" class="document-information"></div>
<div id="internal-metadata" class="document-information">
<dl id="identifiers">
<dt class="label-stream">Stream:</dt>
<dd class="stream">Independent Submission</dd>
<dt class="label-rfc">RFC:</dt>
<dd class="rfc"><a href="https://www.rfc-editor.org/rfc/rfc8904" class="eref">8904</a></dd>
<dt class="label-category">Category:</dt>
<dd class="category">Informational</dd>
<dt class="label-published">Published:</dt>
<dd class="published">
<time datetime="2020-09" class="published">September 2020</time>
    </dd>
<dt class="label-issn">ISSN:</dt>
<dd class="issn">2070-1721</dd>
<dt class="label-authors">Author:</dt>
<dd class="authors">
<div class="author">
      <div class="author-name">A. Vesely</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 8904</h1>
<h1 id="title">DNS Whitelist (DNSWL) Email Authentication Method Extension</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">
This document describes an email authentication method compliant
with RFC 8601.  The method consists of looking up the sender's IP address in a
DNS whitelist.  This document provides information in case the method is seen
in the field, suggests a useful practice, and registers the
relevant keywords.<a href="#section-abstract-1" class="pilcrow">¶</a></p>
<p id="section-abstract-2">
 This document does not consider blacklists.<a href="#section-abstract-2" class="pilcrow">¶</a></p>
</section>
<div id="status-of-memo">
<section id="section-boilerplate.1">
        <h2 id="name-status-of-this-memo">
<a href="#name-status-of-this-memo" class="section-name selfRef">Status of This Memo</a>
        </h2>
<p id="section-boilerplate.1-1">
            This document is not an Internet Standards Track specification; it is
            published for informational purposes.<a href="#section-boilerplate.1-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-2">
            This is a contribution to the RFC Series, independently of any
            other RFC stream.  The RFC Editor has chosen to publish this
            document at its discretion and makes no statement about its value
            for implementation or deployment.  Documents approved for
            publication by the RFC Editor are not candidates for any level of
            Internet Standard; see Section 2 of RFC 7841.<a href="#section-boilerplate.1-2" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <span><a href="https://www.rfc-editor.org/info/rfc8904">https://www.rfc-editor.org/info/rfc8904</a></span>.<a href="#section-boilerplate.1-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="copyright">
<section id="section-boilerplate.2">
        <h2 id="name-copyright-notice">
<a href="#name-copyright-notice" class="section-name selfRef">Copyright Notice</a>
        </h2>
<p id="section-boilerplate.2-1">
            Copyright (c) 2020 IETF Trust and the persons identified as the
            document authors. All rights reserved.<a href="#section-boilerplate.2-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.2-2">
            This document is subject to BCP 78 and the IETF Trust's Legal
            Provisions Relating to IETF Documents
            (<span><a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a></span>) 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.<a href="#section-boilerplate.2-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="toc">
<section id="section-toc.1">
        <a href="#" onclick="scroll(0,0)" class="toplink">▲</a><h2 id="name-table-of-contents">
<a href="#name-table-of-contents" class="section-name selfRef">Table of Contents</a>
        </h2>
<nav class="toc"><ul class="ulEmpty toc compact">
<li class="ulEmpty toc compact" id="section-toc.1-1.1">
            <p id="section-toc.1-1.1.1" class="keepWithNext"><a href="#section-1" class="xref">1</a>.  <a href="#name-introduction" class="xref">Introduction</a><a href="#section-toc.1-1.1.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty toc compact" id="section-toc.1-1.2">
            <p id="section-toc.1-1.2.1" class="keepWithNext"><a href="#section-2" class="xref">2</a>.  <a href="#name-method-details" class="xref">Method Details</a><a href="#section-toc.1-1.2.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty toc compact" id="section-toc.1-1.3">
            <p id="section-toc.1-1.3.1" class="keepWithNext"><a href="#section-3" class="xref">3</a>.  <a href="#name-txt-record-contents" class="xref">TXT Record Contents</a><a href="#section-toc.1-1.3.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty toc compact" id="section-toc.1-1.4">
            <p id="section-toc.1-1.4.1"><a href="#section-4" class="xref">4</a>.  <a href="#name-iana-considerations" class="xref">IANA Considerations</a><a href="#section-toc.1-1.4.1" class="pilcrow">¶</a></p>
<ul class="ulEmpty toc compact">
<li class="ulEmpty toc compact" id="section-toc.1-1.4.2.1">
                <p id="section-toc.1-1.4.2.1.1"><a href="#section-4.1" class="xref">4.1</a>.  <a href="#name-email-authentication-method" class="xref">Email Authentication Methods</a><a href="#section-toc.1-1.4.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="ulEmpty toc compact" id="section-toc.1-1.4.2.2">
                <p id="section-toc.1-1.4.2.2.1"><a href="#section-4.2" class="xref">4.2</a>.  <a href="#name-email-authentication-proper" class="xref">Email Authentication Property Type</a><a href="#section-toc.1-1.4.2.2.1" class="pilcrow">¶</a></p>
</li>
              <li class="ulEmpty toc compact" id="section-toc.1-1.4.2.3">
                <p id="section-toc.1-1.4.2.3.1"><a href="#section-4.3" class="xref">4.3</a>.  <a href="#name-email-authentication-result" class="xref">Email Authentication Result Names</a><a href="#section-toc.1-1.4.2.3.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="ulEmpty toc compact" id="section-toc.1-1.5">
            <p id="section-toc.1-1.5.1"><a href="#section-5" class="xref">5</a>.  <a href="#name-security-considerations" class="xref">Security Considerations</a><a href="#section-toc.1-1.5.1" class="pilcrow">¶</a></p>
<ul class="ulEmpty toc compact">
<li class="ulEmpty toc compact" id="section-toc.1-1.5.2.1">
                <p id="section-toc.1-1.5.2.1.1"><a href="#section-5.1" class="xref">5.1</a>.  <a href="#name-over-quota-signaling" class="xref">Over-Quota Signaling</a><a href="#section-toc.1-1.5.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="ulEmpty toc compact" id="section-toc.1-1.5.2.2">
                <p id="section-toc.1-1.5.2.2.1"><a href="#section-5.2" class="xref">5.2</a>.  <a href="#name-security-of-dnssec-validati" class="xref">Security of DNSSEC Validation</a><a href="#section-toc.1-1.5.2.2.1" class="pilcrow">¶</a></p>
</li>
              <li class="ulEmpty toc compact" id="section-toc.1-1.5.2.3">
                <p id="section-toc.1-1.5.2.3.1"><a href="#section-5.3" class="xref">5.3</a>.  <a href="#name-inherited-security-consider" class="xref">Inherited Security Considerations</a><a href="#section-toc.1-1.5.2.3.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="ulEmpty toc compact" id="section-toc.1-1.6">
            <p id="section-toc.1-1.6.1"><a href="#section-6" class="xref">6</a>.  <a href="#name-references" class="xref">References</a><a href="#section-toc.1-1.6.1" class="pilcrow">¶</a></p>
<ul class="ulEmpty toc compact">
<li class="ulEmpty toc compact" id="section-toc.1-1.6.2.1">
                <p id="section-toc.1-1.6.2.1.1"><a href="#section-6.1" class="xref">6.1</a>.  <a href="#name-normative-references" class="xref">Normative References</a><a href="#section-toc.1-1.6.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="ulEmpty toc compact" id="section-toc.1-1.6.2.2">
                <p id="section-toc.1-1.6.2.2.1"><a href="#section-6.2" class="xref">6.2</a>.  <a href="#name-informative-references" class="xref">Informative References</a><a href="#section-toc.1-1.6.2.2.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="ulEmpty toc compact" id="section-toc.1-1.7">
            <p id="section-toc.1-1.7.1"><a href="#section-appendix.a" class="xref">Appendix A</a>.  <a href="#name-example" class="xref">Example</a><a href="#section-toc.1-1.7.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty toc compact" id="section-toc.1-1.8">
            <p id="section-toc.1-1.8.1"><a href="#section-appendix.b" class="xref">Appendix B</a>.  <a href="#name-known-implementation" class="xref">Known Implementation</a><a href="#section-toc.1-1.8.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty toc compact" id="section-toc.1-1.9">
            <p id="section-toc.1-1.9.1"><a href="#section-appendix.c" class="xref">Appendix C</a>.  <a href="#name-future-possibilities-of-the" class="xref">Future Possibilities of the 'dns' ptype</a><a href="#section-toc.1-1.9.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty toc compact" id="section-toc.1-1.10">
            <p id="section-toc.1-1.10.1"><a href="#section-appendix.d" class="xref"></a><a href="#name-authors-address" class="xref">Author's Address</a><a href="#section-toc.1-1.10.1" class="pilcrow">¶</a></p>
</li>
        </ul>
</nav>
</section>
</div>
<section id="section-1">
      <h2 id="name-introduction">
<a href="#section-1" class="section-number selfRef">1. </a><a href="#name-introduction" class="section-name selfRef">Introduction</a>
      </h2>
<p id="section-1-1">
 One of the many checks that mail servers carry out is to query DNS
 whitelists (DNSWLs).
 That method is fully discussed in <span>[<a href="#RFC5782" class="xref">RFC5782</a>]</span>.
 The DNS <span>[<a href="#RFC1034" class="xref">RFC1034</a>]</span> 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 127.0.0.0/8.  Depending
 on
 the query, TXT records with varying content can also be retrieved.
 Query examples are given in <a href="#example" class="xref">Appendix A</a>.<a href="#section-1-1" class="pilcrow">¶</a></p>
<p id="section-1-2">
 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 <span><a href="https://www.rfc-editor.org/rfc/rfc7208#appendix-D.3" class="relref">Appendix D.3</a> of [<a href="#RFC7208" class="xref">RFC7208</a>]</span> is also illustrated in
 <a href="#example" class="xref">Appendix A</a>). 
 In addition, the result of a DNSWL
 lookup can 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 to provide.<a href="#section-1-2" class="pilcrow">¶</a></p>
<p id="section-1-3">
 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
 <span>[<a href="#RFC5782" class="xref">RFC5782</a>]</span>.  There are also
 blacklists/blocklists (DNSBLs) and combined lists.  Since they all have
 the same structure, the abbreviation DNSxL is used to mean any.  The
 core procedures of a Mail Transfer Agent (MTA) tend to be quite
 general, leaving particular cases to be handled by add-on modules.  In
 the case of combined lists, the boundary MTA (see <span>[<a href="#RFC5598" class="xref">RFC5598</a>]</span>), which carries out the check and
 possibly stores the result, has to be able to discern at least the
 color of each entry, as that is required to make accept/reject
 decisions.  This document provides for storing the result when the
 DNSxL record to be reported is a whitelisting one.<a href="#section-1-3" class="pilcrow">¶</a></p>
<p id="section-1-4">
 Data conveyed in A and TXT records can be stored as properties
 of the method.  The meaning of such data varies widely at the mercy
 of the list operator; hence, the queried zone has to be stored as
 well.
 Mail site operators who configure their MTAs to query specific
 DNWSLs marry the policies of those lists, as, in effect, they
 become tantamount to local policies, albeit outsourced.  

Downstream agents who know DNSWL-specific encoding and understand the meaning
of that data can use it to make delivery or display decisions.  For example,
a mail filter that detects heuristic evidence of a scam can counterweight such
information with the trustworthiness score encoded in the A response so as to
protect against false positives.  Mail User Agents (MUAs) can display those
results or use them to decide how to report abusive messages, if configured to
do so.<a href="#section-1-4" class="pilcrow">¶</a></p>
<p id="section-1-5">
 This document describes a usage of
 TXT fields consistent with other authentication methods,
 namely to serve the domain name in the TXT record.  That way,
 a downstream filter could also consider whether the sending agent
 is aligned with the author domain, with semantics similar to
 <span>[<a href="#RFC7489" class="xref">RFC7489</a>]</span>.<a href="#section-1-5" class="pilcrow">¶</a></p>
<p id="section-1-6">
 At the time of this writing, this method is implemented by Courier-MTA
 <span>[<a href="#Courier-MTA" class="xref">Courier-MTA</a>]</span>.  An outline of the
 implementation
 is given in <a href="#implement" class="xref">Appendix B</a>.<a href="#section-1-6" class="pilcrow">¶</a></p>
</section>
<div id="mresults">
<section id="section-2">
      <h2 id="name-method-details">
<a href="#section-2" class="section-number selfRef">2. </a><a href="#name-method-details" class="section-name selfRef">Method Details</a>
      </h2>
<p id="section-2-1">
 The result of the method states how the query did, up to the
 interpretation of the returned data.<a href="#section-2-1" class="pilcrow">¶</a></p>
<p id="section-2-2">
 The method has four possible results:<a href="#section-2-2" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-2-3">
        <dt id="section-2-3.1">pass:</dt>
        <dd style="margin-left: 6.5em" id="section-2-3.2">
   The query successfully returned applicable
   records.  This result is usually accompanied
   by one or both of the policy properties
   described below.  Since the list is configured
   as a DNSWL, agents unable to interpret
   list-specific properties can still derive a
   positive value from the fact that the sender
   is whitelisted.<a href="#section-2-3.2" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-3.3">none:</dt>
        <dd style="margin-left: 6.5em" id="section-2-3.4">
   The query worked but yielded no A record or returned
   NXDOMAIN, so the sender is not whitelisted.<a href="#section-2-3.4" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-3.5">temperror:</dt>
        <dd style="margin-left: 6.5em" id="section-2-3.6">
   The DNS evaluation could not be completed due to some
   error that is likely transient in nature, such as a temporary DNS
   error (e.g., a DNS RCODE of 2, commonly known as SERVFAIL) or
   other error condition.  A later attempt may produce a
   final result.<a href="#section-2-3.6" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-3.7">permerror:</dt>
        <dd style="margin-left: 6.5em" id="section-2-3.8">
   The DNS evaluation cannot work because test entries don't
   work (that is, DNSWL is broken) or because queries are over quota
   (reported by a DNS RCODE of 5, commonly known as REFUSED, or by a
   DNSWL-specific
   property (policy.ip, defined below) with the same meaning).
   A later attempt is unlikely to produce a final result.
   Human intervention is required.<a href="#section-2-3.8" class="pilcrow">¶</a>
</dd>
      <dd class="break"></dd>
</dl>
<p id="section-2-4">
 Note that there is no "fail" result.<a href="#section-2-4" class="pilcrow">¶</a></p>
<p id="section-2-5">
 The following ptype.property items define how the data provided
 by the whitelist lookup can be saved.<a href="#section-2-5" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-2-6">
        <dt id="section-2-6.1">dns.zone:</dt>
        <dd style="margin-left: 6.5em" id="section-2-6.2">
   DNSWL query root domain, which defines the meaning of the
   policy.ip property below.
   Note that an MTA can use a local mirror with a different
   name.  The name stored here has to be the best available
   reference for all foreseeable downstream consumers.
   Setting dns.zone to the global zone makes the result
   intelligible even if the message is handed outside of the
   internal network.<a href="#section-2-6.2" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-6.3">policy.ip:</dt>
        <dd style="margin-left: 6.5em" id="section-2-6.4">
   The bit mask value received in type A response,
   in dotted quad notation.
   Multiple entries can be arranged in a quoted, comma-separated list
   (quotes are necessary because commas are not allowed in a token).<a href="#section-2-6.4" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-6.5">policy.txt:</dt>
        <dd style="margin-left: 6.5em" id="section-2-6.6">
   The TXT record, if any.  Multiple records are concatenated
   in the usual way (explained, for example, in
   <span><a href="https://www.rfc-editor.org/rfc/rfc7208#section-3.3" class="relref">Section 3.3</a> of [<a href="#RFC7208" class="xref">RFC7208</a>]</span>).
   See <a href="#TXTrecord" class="xref">Section 3</a> for the resulting
   content and query options.<a href="#section-2-6.6" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-6.7">dns.sec:</dt>
        <dd style="margin-left: 6.5em" id="section-2-6.8">
          <p id="section-2-6.8.1">
     This is a generic property stating whether the relevant
     data was validated using DNSSEC <span>[<a href="#RFC4033" class="xref">RFC4033</a>]</span>. 
     For the present method, the relevant data consists of the
     reported policy properties above or, if the method result
     is "none", its nonexistence.
     This property has three possible values:<a href="#section-2-6.8.1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-2-6.8.2">
            <dt id="section-2-6.8.2.1">yes:</dt>
            <dd style="margin-left: 3.0em" id="section-2-6.8.2.2">
       DNSSEC validation confirms the integrity of data.
       <a href="#seccon" class="xref">Section 5.2</a>
       considers how that is 
       related to the DNS response.<a href="#section-2-6.8.2.2" class="pilcrow">¶</a>
</dd>
            <dd class="break"></dd>
<dt id="section-2-6.8.2.3">no:</dt>
            <dd style="margin-left: 3.0em" id="section-2-6.8.2.4">
       The data is not signed.  See <a href="#seccon" class="xref">Section 5.2</a>.<a href="#section-2-6.8.2.4" class="pilcrow">¶</a>
</dd>
            <dd class="break"></dd>
<dt id="section-2-6.8.2.5">na:</dt>
            <dd style="margin-left: 3.0em" id="section-2-6.8.2.6">
Not applicable.  No DNSSEC validation can be performed, possibly because the
lookup is run through a different means than a security-aware DNS resolver.
This does not necessarily imply less security.  In particular, "na" is used if
the data was downloaded in bulk and then loaded on a local nameserver, which
is the case of an MTA querying a local zone different from the reported
dns.zone.  DNS errors, including validation errors, can also report "na".
This is also the value assumed by default.<a href="#section-2-6.8.2.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
</dl>
</dd>
      <dd class="break"></dd>
</dl>
</section>
</div>
<div id="TXTrecord">
<section id="section-3">
      <h2 id="name-txt-record-contents">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-txt-record-contents" class="section-name selfRef">TXT Record Contents</a>
      </h2>
<p id="section-3-1">
 According to <span>[<a href="#RFC5782" class="xref">RFC5782</a>]</span>, TXT records
 describe
 the reason why IP addresses are listed in a DNSWL.
 An example of a DNSWL whose TXT records contain the domain name
 of the organization assignee of the sending IP is given in
 <a href="#implement" class="xref">Appendix B</a>.
 The domain name would correspond to the DNS domain
 name used by or within the Administrative Management Domain (ADMD)
 operating
 the relevant MTA, sometimes called the "organizational domain".
 In that case, the authentication provided by this method is
 equivalent to a DomainKeys Identified Mail (DKIM) signature
 <span>[<a href="#RFC6376" class="xref">RFC6376</a>]</span> or 
 an SPF check host <span>[<a href="#RFC7208" class="xref">RFC7208</a>]</span>, if the
 DNSWL is
 trusted.<a href="#section-3-1" class="pilcrow">¶</a></p>
<p id="section-3-2">
 According to a DNSWL's policy, attributing responsibility of an
 IP address to an organization may require something more than a
 mere PTR record consistency.
 If no domain names can be responsibly associated to a given IP
 address, for example, because the IP address was added without direct
 involvement of the organization concerned, DNSWLs can use a
 subdomain of .INVALID <span>[<a href="#RFC2606" class="xref">RFC2606</a>]</span> where
 the leftmost
 label hints at why an address is whitelisted.
 For example, if the address 192.0.2.38 was added by the list
 managers solely based on their knowledge, the corresponding TXT
 record might be AUTOPROMOTED.INVALID so as to avoid explicitly
 identifying an entity that didn't opt in.<a href="#section-3-2" class="pilcrow">¶</a></p>
<p id="section-3-3">
 Following the example of Multicast DNS (see the second
 paragraph of <span><a href="https://www.rfc-editor.org/rfc/rfc6762#section-16" class="relref">Section 16</a> of [<a href="#RFC6762" class="xref">RFC6762</a>]</span>), names containing non-ASCII characters can be
 encoded in UTF-8 <span>[<a href="#RFC3629" class="xref">RFC3629</a>]</span>
 using the Normalization Form C <span>[<a href="#NFC" class="xref">NFC</a>]</span>,
 as
 described in "Unicode Format for Network Interchange" <span>[<a href="#RFC5198" class="xref">RFC5198</a>]</span>.  Inclusion of unaltered
 UTF-8 TXT values in the header entails an environment
 compatible with Email Address Internationalization (EAI) <span>[<a href="#RFC6530" class="xref">RFC6530</a>]</span>.<a href="#section-3-3" class="pilcrow">¶</a></p>
<p id="section-3-4">
 DNS queries with a QTYPE of ANY may lead to inconsistent replies,
 depending on the cache status.  In addition, ANY is not "all",
 and the provisions for queries that have QTYPE=ANY
 <span>[<a href="#RFC8482" class="xref">RFC8482</a>]</span> don't cover DNSxLs.
 A mail server can issue two simultaneous queries, A and TXT.
 Otherwise, a downstream filter can issue a TXT query on its own,
 if it knows that an A query was successful and that the DNSWL
 serves useful TXT records.
 It is unlikely that TXT records exist if a query for QTYPE A
 brought a result of "none".<a href="#section-3-4" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-4">
      <h2 id="name-iana-considerations">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<p id="section-4-1">
 IANA maintains the "Email Authentication Parameters" registry with
 several subregistries.  IANA has made the assignments 
 set out in the following sections.<a href="#section-4-1" class="pilcrow">¶</a></p>
<section id="section-4.1">
        <h3 id="name-email-authentication-method">
<a href="#section-4.1" class="section-number selfRef">4.1. </a><a href="#name-email-authentication-method" class="section-name selfRef">Email Authentication Methods</a>
        </h3>
<p id="section-4.1-1">
IANA has created four new entries in the "Email Authentication Methods"
registry as follows.<a href="#section-4.1-1" class="pilcrow">¶</a></p>
<table class="center" id="table-1">
          <caption><a href="#table-1" class="selfRef">Table 1</a></caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Method</th>
              <th class="text-left" rowspan="1" colspan="1">Definition</th>
              <th class="text-left" rowspan="1" colspan="1">ptype</th>
              <th class="text-left" rowspan="1" colspan="1">property</th>
              <th class="text-left" rowspan="1" colspan="1">Value</th>
              <th class="text-left" rowspan="1" colspan="1">Status</th>
              <th class="text-left" rowspan="1" colspan="1">Version</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">dnswl</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8904</td>
              <td class="text-left" rowspan="1" colspan="1">dns</td>
              <td class="text-left" rowspan="1" colspan="1">zone</td>
              <td class="text-left" rowspan="1" colspan="1">
                <p id="section-4.1-2.2.1.5.1">DNSWL publicly accessible query root domain<a href="#section-4.1-2.2.1.5.1" class="pilcrow">¶</a></p>
</td>
              <td class="text-left" rowspan="1" colspan="1">active</td>
              <td class="text-center" rowspan="1" colspan="1">1</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">dnswl</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8904</td>
              <td class="text-left" rowspan="1" colspan="1">policy</td>
              <td class="text-left" rowspan="1" colspan="1">ip</td>
              <td class="text-left" rowspan="1" colspan="1">
                <p id="section-4.1-2.2.2.5.1">type A response received (or a quoted,
      comma-separated list thereof)<a href="#section-4.1-2.2.2.5.1" class="pilcrow">¶</a></p>
</td>
              <td class="text-left" rowspan="1" colspan="1">active</td>
              <td class="text-center" rowspan="1" colspan="1">1</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">dnswl</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8904</td>
              <td class="text-left" rowspan="1" colspan="1">policy</td>
              <td class="text-left" rowspan="1" colspan="1">txt</td>
              <td class="text-left" rowspan="1" colspan="1">type TXT query response</td>
              <td class="text-left" rowspan="1" colspan="1">active</td>
              <td class="text-center" rowspan="1" colspan="1">1</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">dnswl</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8904</td>
              <td class="text-left" rowspan="1" colspan="1">dns</td>
              <td class="text-left" rowspan="1" colspan="1">sec</td>
              <td class="text-left" rowspan="1" colspan="1">one of "yes" for DNSSEC authenticated data, "no" for
      not signed, or "na" for not applicable</td>
              <td class="text-left" rowspan="1" colspan="1">active</td>
              <td class="text-center" rowspan="1" colspan="1">1</td>
            </tr>
          </tbody>
        </table>
</section>
<div id="ptype">
<section id="section-4.2">
        <h3 id="name-email-authentication-proper">
<a href="#section-4.2" class="section-number selfRef">4.2. </a><a href="#name-email-authentication-proper" class="section-name selfRef">Email Authentication Property Type</a>
        </h3>
<p id="section-4.2-1">
   IANA has created a new entry in the "Email Authentication
   Property Types" registry as follows.<a href="#section-4.2-1" class="pilcrow">¶</a></p>
<table class="center" id="table-2">
          <caption><a href="#table-2" class="selfRef">Table 2</a></caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">ptype</th>
              <th class="text-left" rowspan="1" colspan="1">Definition</th>
              <th class="text-left" rowspan="1" colspan="1">Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">dns</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8904</td>
              <td class="text-left" rowspan="1" colspan="1">The property being reported belongs to the
       Domain Name System.</td>
            </tr>
          </tbody>
        </table>
</section>
</div>
<section id="section-4.3">
        <h3 id="name-email-authentication-result">
<a href="#section-4.3" class="section-number selfRef">4.3. </a><a href="#name-email-authentication-result" class="section-name selfRef">Email Authentication Result Names</a>
        </h3>
<p id="section-4.3-1">
   IANA has created four new entries in the "Email
   Authentication Result Names" registry as follows.<a href="#section-4.3-1" class="pilcrow">¶</a></p>
<table class="center" id="table-3">
          <caption><a href="#table-3" class="selfRef">Table 3</a></caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Auth Method</th>
              <th class="text-left" rowspan="1" colspan="1">Code</th>
              <th class="text-left" rowspan="1" colspan="1">Specification</th>
              <th class="text-left" rowspan="1" colspan="1">Status</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">dnswl</td>
              <td class="text-left" rowspan="1" colspan="1">pass</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8904</td>
              <td class="text-left" rowspan="1" colspan="1">active</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">dnswl</td>
              <td class="text-left" rowspan="1" colspan="1">none</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8904</td>
              <td class="text-left" rowspan="1" colspan="1">active</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">dnswl</td>
              <td class="text-left" rowspan="1" colspan="1">temperror</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8904</td>
              <td class="text-left" rowspan="1" colspan="1">active</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">dnswl</td>
              <td class="text-left" rowspan="1" colspan="1">permerror</td>
              <td class="text-left" rowspan="1" colspan="1">RFC 8904</td>
              <td class="text-left" rowspan="1" colspan="1">active</td>
            </tr>
          </tbody>
        </table>
</section>
</section>
<section id="section-5">
      <h2 id="name-security-considerations">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-security-considerations" class="section-name selfRef">Security Considerations</a>
      </h2>
<section id="section-5.1">
        <h3 id="name-over-quota-signaling">
<a href="#section-5.1" class="section-number selfRef">5.1. </a><a href="#name-over-quota-signaling" class="section-name selfRef">Over-Quota Signaling</a>
        </h3>
<p id="section-5.1-1">
   Some DNSWLs that provide for free access below a given quota
   are known to return special codes to signal that the
   quota has been exceeded (for
   example, 127.0.0.255).
   If the MTA cannot interpret that value, that case results
   in a false positive.
   It can accept messages that it would otherwise reject.
   A DNSWL-specific module would realize this fact and call for
   human intervention.<a href="#section-5.1-1" class="pilcrow">¶</a></p>
<p id="section-5.1-2">
   Returning an RCODE 5 (REFUSED) conveys the
   concept that the query is "unauthorized" and human
   intervention required.<a href="#section-5.1-2" class="pilcrow">¶</a></p>
</section>
<div id="seccon">
<section id="section-5.2">
        <h3 id="name-security-of-dnssec-validati">
<a href="#section-5.2" class="section-number selfRef">5.2. </a><a href="#name-security-of-dnssec-validati" class="section-name selfRef">Security of DNSSEC Validation</a>
        </h3>
<p id="section-5.2-1">
   The dns.sec property is meant to be as secure as DNSSEC results.
   It makes sense to use it in an environment where the DNSSEC
   validation can succeed.<a href="#section-5.2-1" class="pilcrow">¶</a></p>
<p id="section-5.2-2">
   <span><a href="https://www.rfc-editor.org/rfc/rfc4033#section-7" class="relref">Section 7</a> of [<a href="#RFC4033" class="xref">RFC4033</a>]</span> examines various ways of
   setting up a stub resolver that either validates DNSSEC locally
   or trusts the validation provided through a secure
   channel.

For a different class, it is possible to set up a dedicated,
caching, DNSSEC-enabled resolver reachable by the mail
server through interprocess communication on 127.0.0.1.
In such cases, the property dns.sec=yes corresponds to the
Authenticated Data (AD) bit in the DNS response header.<a href="#section-5.2-2" class="pilcrow">¶</a></p>
<p id="section-5.2-3">
   When the response contains no DNSSEC data, a security-aware
   resolver seeks a signed proof of the nonexistence
   of a DS record at some delegation point.  If no error is
   returned, the zone is unsigned and dns.sec=no can be set.
   The Security Considerations section of <span>[<a href="#RFC3225" class="xref">RFC3225</a>]</span> states:<a href="#section-5.2-3" class="pilcrow">¶</a></p>
<blockquote id="section-5.2-4">
   The absence of DNSSEC data in response to a query with the DO bit set
   MUST NOT be taken to mean no security information is available for
   that zone as the response may be forged or a non-forged response of
   an altered (DO bit cleared) query.<a href="#section-5.2-4" class="pilcrow">¶</a>
</blockquote>
<p id="section-5.2-5">
   If the application verifies the DNSSEC signatures on its
   own, it effectively behaves like a validating resolver
   and hence can set dns.sec correspondingly.<a href="#section-5.2-5" class="pilcrow">¶</a></p>
<p id="section-5.2-6">
   When the data is downloaded in bulk and made available on a
   trusted channel without using DNSSEC, the application sets dns.sec=na or not
   at all. For example, consider DNSWLs that publish bulk versions of
   their data duly signed using OpenPGP <span>[<a href="#RFC4880" class="xref">RFC4880</a>]</span>. 
   It is the responsibility of system administrators to
   authenticate the data by downloading and validating the signature.
   The result of such validation is not reported using dns.sec.<a href="#section-5.2-6" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-5.3">
        <h3 id="name-inherited-security-consider">
<a href="#section-5.3" class="section-number selfRef">5.3. </a><a href="#name-inherited-security-consider" class="section-name selfRef">Inherited Security Considerations</a>
        </h3>
<p id="section-5.3-1">
   For DNSSEC, the considerations of <span><a href="https://www.rfc-editor.org/rfc/rfc4033#section-12" class="relref">Section 12</a> of [<a href="#RFC4033" class="xref">RFC4033</a>]</span> apply.<a href="#section-5.3-1" class="pilcrow">¶</a></p>
<p id="section-5.3-2">
   All of the considerations described in
   <span><a href="https://www.rfc-editor.org/rfc/rfc8601#section-7" class="relref">Section 7</a> of [<a href="#RFC8601" class="xref">RFC8601</a>]</span> apply.
   That includes securing against tampering all the channels after
   the production of the Authentication-Results header field.<a href="#section-5.3-2" class="pilcrow">¶</a></p>
<p id="section-5.3-3">
   In addition, the usual caveats apply about importing text from
   external online sources.  Although queried DNSWLs are well-known,
   trusted entities, it is suggested that TXT records be reported
   only if, upon inspection, their content is deemed actionable
   and their format compatible with the computing environment.<a href="#section-5.3-3" class="pilcrow">¶</a></p>
</section>
</section>
<section id="section-6">
      <h2 id="name-references">
<a href="#section-6" class="section-number selfRef">6. </a><a href="#name-references" class="section-name selfRef">References</a>
      </h2>
<section id="section-6.1">
        <h3 id="name-normative-references">
<a href="#section-6.1" class="section-number selfRef">6.1. </a><a href="#name-normative-references" class="section-name selfRef">Normative References</a>
        </h3>
<dl class="references">
<dt id="RFC2606">[RFC2606]</dt>
        <dd>
<span class="refAuthor">Eastlake 3rd, D.</span><span class="refAuthor"> and A. Panitz</span>, <span class="refTitle">"Reserved Top Level DNS Names"</span>, <span class="seriesInfo">BCP 32</span>, <span class="seriesInfo">RFC 2606</span>, <span class="seriesInfo">DOI 10.17487/RFC2606</span>, <time datetime="1999-06" class="refDate">June 1999</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2606">https://www.rfc-editor.org/info/rfc2606</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5782">[RFC5782]</dt>
        <dd>
<span class="refAuthor">Levine, J.</span>, <span class="refTitle">"DNS Blacklists and Whitelists"</span>, <span class="seriesInfo">RFC 5782</span>, <span class="seriesInfo">DOI 10.17487/RFC5782</span>, <time datetime="2010-02" class="refDate">February 2010</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5782">https://www.rfc-editor.org/info/rfc5782</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8601">[RFC8601]</dt>
      <dd>
<span class="refAuthor">Kucherawy, M.</span>, <span class="refTitle">"Message Header Field for Indicating Message Authentication Status"</span>, <span class="seriesInfo">RFC 8601</span>, <span class="seriesInfo">DOI 10.17487/RFC8601</span>, <time datetime="2019-05" class="refDate">May 2019</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8601">https://www.rfc-editor.org/info/rfc8601</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
<section id="section-6.2">
        <h3 id="name-informative-references">
<a href="#section-6.2" class="section-number selfRef">6.2. </a><a href="#name-informative-references" class="section-name selfRef">Informative References</a>
        </h3>
<dl class="references">
<dt id="RFC1034">[RFC1034]</dt>
        <dd>
<span class="refAuthor">Mockapetris, P.</span>, <span class="refTitle">"Domain names - concepts and facilities"</span>, <span class="seriesInfo">STD 13</span>, <span class="seriesInfo">RFC 1034</span>, <span class="seriesInfo">DOI 10.17487/RFC1034</span>, <time datetime="1987-11" class="refDate">November 1987</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc1034">https://www.rfc-editor.org/info/rfc1034</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3225">[RFC3225]</dt>
        <dd>
<span class="refAuthor">Conrad, D.</span>, <span class="refTitle">"Indicating Resolver Support of DNSSEC"</span>, <span class="seriesInfo">RFC 3225</span>, <span class="seriesInfo">DOI 10.17487/RFC3225</span>, <time datetime="2001-12" class="refDate">December 2001</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3225">https://www.rfc-editor.org/info/rfc3225</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3629">[RFC3629]</dt>
        <dd>
<span class="refAuthor">Yergeau, F.</span>, <span class="refTitle">"UTF-8, a transformation format of ISO 10646"</span>, <span class="seriesInfo">STD 63</span>, <span class="seriesInfo">RFC 3629</span>, <span class="seriesInfo">DOI 10.17487/RFC3629</span>, <time datetime="2003-11" class="refDate">November 2003</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3629">https://www.rfc-editor.org/info/rfc3629</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4033">[RFC4033]</dt>
        <dd>
<span class="refAuthor">Arends, R.</span><span class="refAuthor">, Austein, R.</span><span class="refAuthor">, Larson, M.</span><span class="refAuthor">, Massey, D.</span><span class="refAuthor">, and S. Rose</span>, <span class="refTitle">"DNS Security Introduction and Requirements"</span>, <span class="seriesInfo">RFC 4033</span>, <span class="seriesInfo">DOI 10.17487/RFC4033</span>, <time datetime="2005-03" class="refDate">March 2005</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4033">https://www.rfc-editor.org/info/rfc4033</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4880">[RFC4880]</dt>
        <dd>
<span class="refAuthor">Callas, J.</span><span class="refAuthor">, Donnerhacke, L.</span><span class="refAuthor">, Finney, H.</span><span class="refAuthor">, Shaw, D.</span><span class="refAuthor">, and R. Thayer</span>, <span class="refTitle">"OpenPGP Message Format"</span>, <span class="seriesInfo">RFC 4880</span>, <span class="seriesInfo">DOI 10.17487/RFC4880</span>, <time datetime="2007-11" class="refDate">November 2007</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4880">https://www.rfc-editor.org/info/rfc4880</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5198">[RFC5198]</dt>
        <dd>
<span class="refAuthor">Klensin, J.</span><span class="refAuthor"> and M. Padlipsky</span>, <span class="refTitle">"Unicode Format for Network Interchange"</span>, <span class="seriesInfo">RFC 5198</span>, <span class="seriesInfo">DOI 10.17487/RFC5198</span>, <time datetime="2008-03" class="refDate">March 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5198">https://www.rfc-editor.org/info/rfc5198</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5598">[RFC5598]</dt>
        <dd>
<span class="refAuthor">Crocker, D.</span>, <span class="refTitle">"Internet Mail Architecture"</span>, <span class="seriesInfo">RFC 5598</span>, <span class="seriesInfo">DOI 10.17487/RFC5598</span>, <time datetime="2009-07" class="refDate">July 2009</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5598">https://www.rfc-editor.org/info/rfc5598</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6376">[RFC6376]</dt>
        <dd>
<span class="refAuthor">Crocker, D., Ed.</span><span class="refAuthor">, Hansen, T., Ed.</span><span class="refAuthor">, and M. Kucherawy, Ed.</span>, <span class="refTitle">"DomainKeys Identified Mail (DKIM) Signatures"</span>, <span class="seriesInfo">STD 76</span>, <span class="seriesInfo">RFC 6376</span>, <span class="seriesInfo">DOI 10.17487/RFC6376</span>, <time datetime="2011-09" class="refDate">September 2011</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6376">https://www.rfc-editor.org/info/rfc6376</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6530">[RFC6530]</dt>
        <dd>
<span class="refAuthor">Klensin, J.</span><span class="refAuthor"> and Y. Ko</span>, <span class="refTitle">"Overview and Framework for Internationalized Email"</span>, <span class="seriesInfo">RFC 6530</span>, <span class="seriesInfo">DOI 10.17487/RFC6530</span>, <time datetime="2012-02" class="refDate">February 2012</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6530">https://www.rfc-editor.org/info/rfc6530</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6762">[RFC6762]</dt>
        <dd>
<span class="refAuthor">Cheshire, S.</span><span class="refAuthor"> and M. Krochmal</span>, <span class="refTitle">"Multicast DNS"</span>, <span class="seriesInfo">RFC 6762</span>, <span class="seriesInfo">DOI 10.17487/RFC6762</span>, <time datetime="2013-02" class="refDate">February 2013</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6762">https://www.rfc-editor.org/info/rfc6762</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7208">[RFC7208]</dt>
        <dd>
<span class="refAuthor">Kitterman, S.</span>, <span class="refTitle">"Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1"</span>, <span class="seriesInfo">RFC 7208</span>, <span class="seriesInfo">DOI 10.17487/RFC7208</span>, <time datetime="2014-04" class="refDate">April 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7208">https://www.rfc-editor.org/info/rfc7208</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7489">[RFC7489]</dt>
        <dd>
<span class="refAuthor">Kucherawy, M., Ed.</span><span class="refAuthor"> and E. Zwicky, Ed.</span>, <span class="refTitle">"Domain-based Message Authentication, Reporting, and Conformance (DMARC)"</span>, <span class="seriesInfo">RFC 7489</span>, <span class="seriesInfo">DOI 10.17487/RFC7489</span>, <time datetime="2015-03" class="refDate">March 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7489">https://www.rfc-editor.org/info/rfc7489</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8460">[RFC8460]</dt>
        <dd>
<span class="refAuthor">Margolis, D.</span><span class="refAuthor">, Brotman, A.</span><span class="refAuthor">, Ramakrishnan, B.</span><span class="refAuthor">, Jones, J.</span><span class="refAuthor">, and M. Risher</span>, <span class="refTitle">"SMTP TLS Reporting"</span>, <span class="seriesInfo">RFC 8460</span>, <span class="seriesInfo">DOI 10.17487/RFC8460</span>, <time datetime="2018-09" class="refDate">September 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8460">https://www.rfc-editor.org/info/rfc8460</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8482">[RFC8482]</dt>
        <dd>
<span class="refAuthor">Abley, J.</span><span class="refAuthor">, Gudmundsson, O.</span><span class="refAuthor">, Majkowski, M.</span><span class="refAuthor">, and E. Hunt</span>, <span class="refTitle">"Providing Minimal-Sized Responses to DNS Queries That Have QTYPE=ANY"</span>, <span class="seriesInfo">RFC 8482</span>, <span class="seriesInfo">DOI 10.17487/RFC8482</span>, <time datetime="2019-01" class="refDate">January 2019</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8482">https://www.rfc-editor.org/info/rfc8482</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="Courier-MTA">[Courier-MTA]</dt>
        <dd>
<span class="refTitle">"Courier Mail Server"</span>, <span>&lt;<a href="https://www.courier-mta.org/">https://www.courier-mta.org/</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="DNSWL">[DNSWL]</dt>
        <dd>
<span class="refTitle">"dnswl.org - E-Mail Reputation - Protect against false positives"</span>, <span>&lt;<a href="https://www.dnswl.org/">https://www.dnswl.org/</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="NFC">[NFC]</dt>
      <dd>
<span class="refAuthor">Whistler, K., Ed.</span>, <span class="refTitle">"Unicode Normalization Forms"</span>, <span class="seriesInfo">Unicode Standard Annex 15</span>, <time datetime="2020-02" class="refDate">February 2020</time>, <span>&lt;<a href="https://www.unicode.org/reports/tr15/tr15-50.html">https://www.unicode.org/reports/tr15/tr15-50.html</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
</section>
<div id="example">
<section id="section-appendix.a">
      <h2 id="name-example">
<a href="#section-appendix.a" class="section-number selfRef">Appendix A. </a><a href="#name-example" class="section-name selfRef">Example</a>
      </h2>
<span id="name-trace-fields-at-the-top-of-"></span><figure id="figure-1">
        <div id="section-appendix.a-1.1">
<pre class="sourcecode">
Delivered-To: recipient@example.org
Return-Path: &lt;sender@example.com&gt;
Authentication-Results: mta.example.org;
  dkim=pass (whitelisted) header.i=@example.com
Authentication-Results: mta.example.org;
  dnswl=pass dns.zone=list.dnswl.example dns.sec=na
  policy.ip=127.0.10.1
  policy.txt="fwd.example https://dnswl.example/?d=fwd.example"
Received-SPF: fail (Address does not pass Sender Policy Framework)
  client-ip=2001:db8::2:1;
  envelope-from="sender@example.com";
  helo=mail.fwd.example;
  receiver=mta.example.org;
Received: from mail.fwd.example (mail.fwd.example [2001:db8::2:1])
  (TLS: TLSv1/SSLv3,128bits,ECDHE-RSA-AES128-GCM-SHA256)
  by mta.example.org with ESMTPS; Thu, 03 Oct 2019 19:23:11 +0200
  id 00000000005DC044.000000005702D87C.000007FC
</pre>
</div>
<figcaption><a href="#figure-1" class="selfRef">Figure 1</a>:
<a href="#name-trace-fields-at-the-top-of-" class="selfRef">Trace Fields at the Top of the Header</a>
        </figcaption></figure>
<p id="section-appendix.a-2">The message went through a third party, fwd.example, which forwarded
      it to the final MTA.  The mail path was not arranged beforehand with
      the involved MTAs; it emerged spontaneously.  This message would not
      have
      made it to the target without whitelisting, because:<a href="#section-appendix.a-2" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-appendix.a-3.1">the author domain published a strict SPF policy (-all),<a href="#section-appendix.a-3.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-appendix.a-3.2">the forwarder did not alter the bounce address, and<a href="#section-appendix.a-3.2" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-appendix.a-3.3">the target usually honors reject on fail, according to <span><a href="https://www.rfc-editor.org/rfc/rfc7208#section-8.4" class="relref">Section 8.4</a> of [<a href="#RFC7208" class="xref">RFC7208</a>]</span>.<a href="#section-appendix.a-3.3" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-appendix.a-4">However, the target also implemented the last paragraph of <span><a href="https://www.rfc-editor.org/rfc/rfc7208#appendix-D.3" class="relref">Appendix D.3</a> of [<a href="#RFC7208" class="xref">RFC7208</a>]</span>.  Its behavior
      hinges on the following DNS entries:<a href="#section-appendix.a-4" class="pilcrow">¶</a></p>
<span id="name-dns-resource-records-for-20"></span><figure id="figure-2">
        <div id="section-appendix.a-5.1">
<pre class="sourcecode">
  1.0.0.0.2.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.d.b.8.2.0.0.1.
                                               list.dnswl.example.
       IN  A    127.0.10.1
       IN  TXT  "fwd.example https://dnswl.example/?d=fwd.example"
</pre>
</div>
<figcaption><a href="#figure-2" class="selfRef">Figure 2</a>:
<a href="#name-dns-resource-records-for-20" class="selfRef">DNS Resource Records for 2001:db8::2:1
                (line breaks for editorial reasons)</a>
        </figcaption></figure>
<p id="section-appendix.a-6">If mail.fwd.example had connected from address 192.0.2.1, then
      the query name would have been <code>1.2.0.192.list.dnswl.example</code>.
      See full description in <span>[<a href="#RFC5782" class="xref">RFC5782</a>]</span>.<a href="#section-appendix.a-6" class="pilcrow">¶</a></p>
<p id="section-appendix.a-7">At connection time, because the remote IP address is whitelisted,
      the target MTA did not reject the message before DATA.  Instead, it
      recorded the SPF fail result and indicated the local policy mechanism
      that was applied in order to override that result.
      Subsequent filtering verified DKIM <span>[<a href="#RFC6376" class="xref">RFC6376</a>]</span>.<a href="#section-appendix.a-7" class="pilcrow">¶</a></p>
<p id="section-appendix.a-8">At later stages, mail filters can reject or quarantine the message
      based on its content.
      A deeper knowledge of the policy values obtained from dnswl.example
      allows interpreting the values of policy.ip and weighing them against
      other factors so as to make better decisions.<a href="#section-appendix.a-8" class="pilcrow">¶</a></p>
</section>
</div>
<div id="implement">
<section id="section-appendix.b">
      <h2 id="name-known-implementation">
<a href="#section-appendix.b" class="section-number selfRef">Appendix B. </a><a href="#name-known-implementation" class="section-name selfRef">Known Implementation</a>
      </h2>
<p id="section-appendix.b-1">
 Implementation details mentioned in this section have been
 stable for several years.
 Yet, this description is necessarily superficial, version
 dependent, and subject to change.<a href="#section-appendix.b-1" class="pilcrow">¶</a></p>
<p id="section-appendix.b-2">
 Courier-MTA <span>[<a href="#Courier-MTA" class="xref">Courier-MTA</a>]</span> can be
 configured to look up DNSBLs
 and DNSWLs, with similar command-line switches:<a href="#section-appendix.b-2" class="pilcrow">¶</a></p>
<div id="section-appendix.b-3">
<pre class="sourcecode">
-block=zone[=displayzone][,var[/n.n.n.n][,msg]]
-allow=zone[=displayzone][,var[/n.n.n.n[,]]]
</pre><a href="#section-appendix.b-3" class="pilcrow">¶</a>
</div>
<p id="section-appendix.b-4">
 "zone" is the zone to be queried.<a href="#section-appendix.b-4" class="pilcrow">¶</a></p>
<p id="section-appendix.b-5">
 "displayzone" is only used for -allow; it is the value to be set
 in the dns.zone property.<a href="#section-appendix.b-5" class="pilcrow">¶</a></p>
<p id="section-appendix.b-6">
 "var" stands for the environment variable whose existence triggers
 a special action.  The default variable names result in a
 conventional behavior implemented by Courier-MTA.
 By setting different environment variables,
 users can customize the behavior.  Conventional behavior differs
 widely
 between -block and -allow.  The former rejects the message; the latter
 produces Authentication-Results header fields.<a href="#section-appendix.b-6" class="pilcrow">¶</a></p>
<p id="section-appendix.b-7">
 The n.n.n.n IP address requires a precise A record response.  If
 not given, any response results in setting the corresponding variable.
 If given, variables are set only if the response matches exactly.
 Such syntax provides for a very limited interpretation of the
 information encoded in A records.
 However, it is considered to be too complicated already.
 Even specifying a range, an enumeration of values, or a regular
 expression would require something beyond what a normal user
 would be willing to manage.<a href="#section-appendix.b-7" class="pilcrow">¶</a></p>
<p id="section-appendix.b-8">
 Finally, the trailing message, which overrides the 5xx SMTP reply
 for -block, is not used for -allow, except that its mere presence
 requires querying TXT records to be registered in policy.txt.<a href="#section-appendix.b-8" class="pilcrow">¶</a></p>
<p id="section-appendix.b-9">
 SPF is part of Courier-MTA's core.  It is configured separately
 and provides for an "allowok" keyword to indicate the choice to
 override
 rejection in case of SPF failure and -allow whitelisting.<a href="#section-appendix.b-9" class="pilcrow">¶</a></p>
<p id="section-appendix.b-10">
   A customary whitelist is defined by DNSWL.org <span>[<a href="#DNSWL" class="xref">DNSWL</a>]</span>.  It serves A records
   encoded as follows:<a href="#section-appendix.b-10" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-appendix.b-11">
        <dt id="section-appendix.b-11.1">1st octet:</dt>
        <dd style="margin-left: 1.5em" id="section-appendix.b-11.2">127.<a href="#section-appendix.b-11.2" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-appendix.b-11.3">2nd octet:</dt>
        <dd style="margin-left: 1.5em" id="section-appendix.b-11.4">0.<a href="#section-appendix.b-11.4" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-appendix.b-11.5">3rd octet:</dt>
        <dd style="margin-left: 1.5em" id="section-appendix.b-11.6">Category of business, 15 values.<a href="#section-appendix.b-11.6" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-appendix.b-11.7">4th octet:</dt>
        <dd style="margin-left: 1.5em" id="section-appendix.b-11.8">Trustworthiness/score, 4 values.<a href="#section-appendix.b-11.8" class="pilcrow">¶</a>
</dd>
      <dd class="break"></dd>
</dl>
<p id="section-appendix.b-12">
   They also serve TXT records containing the domain name followed by a
   URL pointing to further information about the relevant organization,
   such as what other IP addresses of theirs are being whitelisted.
   They don't use UTF-8.<a href="#section-appendix.b-12" class="pilcrow">¶</a></p>
<p id="section-appendix.b-13">
 DNSWL.org provides for free
 registration and free access below
 100,000 queries per day.
 They use a special return code, 127.0.0.255 as exemplified above,
 to signal that the quota has been exceeded.


Although Courier-MTA itself does not recognize this return code, it has a mail
filter (zdkimfilter, named after its main usage) that hard codes recognition
of this code and the code for trustworthiness in the 4th octet.<a href="#section-appendix.b-13" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-appendix.c">
      <h2 id="name-future-possibilities-of-the">
<a href="#section-appendix.c" class="section-number selfRef">Appendix C. </a><a href="#name-future-possibilities-of-the" class="section-name selfRef">Future Possibilities of the 'dns' ptype</a>
      </h2>
<p id="section-appendix.c-1">
 The description of the new ptype proposed in <a href="#ptype" class="xref">Section 4.2</a>
 says, "The property being reported belongs to the Domain Name
 System."  That definition can broadly include any tag found in a
 domain's TXT record.  For example, designers of
 authentication methods can
 agree that within a resinfo of a given method, any dns ptype
 refers to tags in the relevant DNS record, unless otherwise
 specified.  So one could have, say:<a href="#section-appendix.c-1" class="pilcrow">¶</a></p>
<div id="section-appendix.c-2">
<pre class="sourcecode">
Authentication-Results: example.com;
  spf=pass smtp.mailfrom=example.net dns.sec=y;
  dkim=pass header.i=@example.org header.b=jIvx30NG dns.s=tlsrpt
</pre><a href="#section-appendix.c-2" class="pilcrow">¶</a>
</div>
<p id="section-appendix.c-3">
 While dns.sec is defined above, albeit not for the spf method,
 the use of tlsrpt in the DKIM record is exemplified in
 <span><a href="https://www.rfc-editor.org/rfc/rfc8460#section-3" class="relref">Section 3</a> of [<a href="#RFC8460" class="xref">RFC8460</a>]</span>.
 The tag s= is part of the DKIM TXT record, not to be confused
 with the selector s=, which is part of a DKIM signature.  Just
 like the latter can be reported as header.s because the DKIM
 header field is in the message header, it may make sense to
 report the former as dns.s because the DKIM DNS record is in the
 DNS.<a href="#section-appendix.c-3" class="pilcrow">¶</a></p>
<p id="section-appendix.c-4">
 NOTE: This is only a hint at what may become a consistent naming
 convention around the new ptype.  In any case, any new property
 using this ptype requires its own formal definition.  This document
 does NOT define the property dns.s=, let alone the service tlsrpt.<a href="#section-appendix.c-4" class="pilcrow">¶</a></p>
</section>
<div id="authors-addresses">
<section id="section-appendix.d">
      <h2 id="name-authors-address">
<a href="#name-authors-address" class="section-name selfRef">Author's Address</a>
      </h2>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Alessandro Vesely</span></div>
<div dir="auto" class="left"><span class="street-address">v. L. Anelli 13</span></div>
<div dir="auto" class="left">
<span class="postal-code">20122</span> <span class="locality">Milano</span> <span class="region">MI</span>
</div>
<div dir="auto" class="left"><span class="country-name">Italy</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:vesely@tana.it" class="email">vesely@tana.it</a>
</div>
</address>
</section>
</div>
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