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IETF                                                           A. Vesely
Internet-Draft
Intended status: Informational                          January 20, 2016
Expires: July 23, 2016


              DNSWL Email Authentication Method Extension
                    draft-vesely-authmethod-dnswl-02

Abstract

   This document describes an additional Email Authentication Method
   compliant with RFC 7601.  The method consists in looking up the
   sender'IP in a DNS whitelist.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on July 23, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Method Results  . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Appendix A.  Example  . . . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   One of the many checks that mail servers carry out is to query DNS
   whitelists (DNSWL, [RFC6471]).  The lookup is based on the sender's
   IP address, so this check can occur very early in an SMTP
   transaction, and can be used to counterweight policies that typically
   occur at early stages too, such as the Sender Policy Framework (SPF,
   [RFC7208]).  Nevertheless, the result of a DNSWL lookup can be used
   at later stages as well; for example, a delivery agent can use it 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 can contain more than pass/fail, but they are encoded
   according to list-specific criteria.  The present method considers
   only whitelists --one of the major branches exemplified by [RFC6471].
   That way, at least the meaning of pass/fail is clear.  Additional
   data is stored in the parameters as-is, and can be interpreted based
   on list-specific knowledge.

2.  Method Results

   dns.zone:   DNSWL query root domain, which defines the meaning of the
               result.  Note that if the MTA uses a local mirror, this
               can be different from the zone actually queried.

   policy.ip:  The bit mask value, in dotted quad.  This entry can be
               repeated if the DNSWL returns multiple A records.

   policy.txt: The TXT record, if any.

   In a strict sense, the result of the method states how the query did:

   pass:       The query successfully returned applicable records.




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   fail:       The query worked, but no applicable record was found.

   temperror:  There was a transient problem with the query.

   permerror:  There is a setup problem, the query cannot work.

3.  IANA Considerations

   There is a registry of Email Authentication Methods created by
   RFC7601.  The method described in this document is referred by
   Table 1, it has three ptype.Property values detailed in Table 2.

                    +--------+--------------+---------+
                    | Method | Defined      | version |
                    +--------+--------------+---------+
                    | dnswl  | [this rfc??] |       1 |
                    +--------+--------------+---------+

               Table 1: Method name, definition, and version

          +--------+----------+-----------------------+--------+
          | ptype  | Property | Value                 | Status |
          +--------+----------+-----------------------+--------+
          | dns    | zone     | The query root domain | active |
          | policy | ip       | type A result         | active |
          | policy | txt      | type TXT result       | active |
          +--------+----------+-----------------------+--------+

                          Table 2: Method values

   In addition, this method reuses four of the values already defined in
   the Email Authentication Result Names associated registry.  They are
   listed in Table 3.

                    +-----------+-----------+--------+
                    | Code      | Meaning   | Status |
                    +-----------+-----------+--------+
                    | pass      | Section 2 | active |
                    | fail      | Section 2 | active |
                    | temperror | Section 2 | active |
                    | permerror | Section 2 | active |
                    +-----------+-----------+--------+

                          Table 3: Method results







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4.  Security Considerations

   All of the considerations described in Section 7 of [RFC7601] apply.

   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 actually actionable.  If
   they contain non-ASCII characters, they need to be encoded as
   appropriate.

5.  References

5.1.  Normative References

   [RFC7208]  Kitterman, S., "Sender Policy Framework (SPF) for
              Authorizing Use of Domains in Email, Version 1", RFC 7208,
              DOI 10.17487/RFC7208, April 2014,
              <http://www.rfc-editor.org/info/rfc7208>.

   [RFC7601]  Kucherawy, M., "Message Header Field for Indicating
              Message Authentication Status", RFC 7601, DOI 10.17487/
              RFC7601, August 2015,
              <http://www.rfc-editor.org/info/rfc7601>.

5.2.  Informative References

   [RFC6471]  Lewis, C. and M. Sergeant, "Overview of Best Email DNS-
              Based List (DNSBL) Operational Practices", RFC 6471, DOI
              10.17487/RFC6471, January 2012,
              <http://www.rfc-editor.org/info/rfc6471>.

Appendix A.  Example

      Authentication-Results: mta.example.com;
          dnswl=pass dns.zone=list.dnswl.example
          policy.ip=127.0.10.1
          policy.txt="example.org http://dnswl.example/s?s=100"

Author's Address

   Alessandro Vesely
   v. L. Anelli 13
   Milano, MI  20122
   IT

   Email: vesely@tana.it




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