[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 8904

IETF                                                           A. Vesely
Internet-Draft                                             July 15, 2013
Intended status: Informational
Expires: January 16, 2014


              DNSWL Email Authentication Method Extension
                    draft-vesely-authmethod-dnswl-00

Abstract

   This document describes a method that can be registered within the
   Email Authentication Methods IANA registry created by RFC 5451.  The
   method consists in looking up a DNS whitelist.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 16, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.





Vesely                  Expires January 16, 2014                [Page 1]


Internet-Draft      DNSWL email-auth-method extension          July 2013


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Method Results  . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Implementation Status . . . . . . . . . . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Appendix A.  Example  . . . . . . . . . . . . . . . . . . . . . . . 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7







































Vesely                  Expires January 16, 2014                [Page 2]


Internet-Draft      DNSWL email-auth-method extension          July 2013


1.  Introduction

   One of the many checks that mail servers carry out is to query DNS
   whitelists (DNSWL, [RFC5782]).  The semantics of DNSWL is similar to
   that of Vouch By Reference (VBR, [RFC5518]); that is, an external
   organization, trusted by the receiving mail transfer agent (MTA),
   vouches for the sender.

   Differently from VBR, the lookup is based on the IP address.  That
   allows it to occur very early in an SMTP transaction, and thus it can
   be used to counterweight policies that typically occur at those early
   stages too, such as the Sender Policy Framework (SPF, [RFC4408]).
   Nevertheless, the result of a DNSWL lookup is likely used at later
   stages as well; for example, a delivery agent can use it to estimate
   the spamminess of an email message.  Reusing the previously obtained
   result is more consistent than issuing multiple queries, and saves
   resources.


2.  Method Results

   In this document, the acronym DNSWL is used both to refer to a
   generic organization that publishes a whitelist, and to indicate the
   use of such service, that is the method.  The organization defines
   the DNS zone and the record type(s) to be queried, as well as the
   meaning of the listings and the procedures to maintain them.

   Unlike other methods, such as dkim or spf, there is little or no work
   to be carried out by the receiving MTA on the values retrieved from
   the DNS query.  As explained in Section 2.3 of [RFC5782], DNSWLs
   encode taxonomical details about the mail sender as bit masks of type
   A records.  The receiving MTA just needs to work out whether the data
   returned is at all applicable.  In that case, it uses that data as an
   outsourced extension of its local policy.  Thus, in a broad sense,
   the result of the method is the content returned by the query:

   dns.zone:   The name of the DNSWL, which defines the meaning of the
               result.  If the MTA uses a private mirror, this can be
               different from the zone actually queried.

   policy.ip:  The bit mask value.  This entry ("propspec" in the
               grammar of [I-D.ietf-appsawg-rfc5451bis]) can be repeated
               if the DNSWL returns multiple A records.

   policy.txt: The TXT record, or the relevant part of it, if any.  This
               can contain a domain name or an abuse reporting address,
               which can be used as described in Section 5.3 of
               [RFC6650].



Vesely                  Expires January 16, 2014                [Page 3]


Internet-Draft      DNSWL email-auth-method extension          July 2013


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

   pass:       The query successfully returned applicable records.

   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
   RFC5451.  The method described in this document is referred by
   Table 1, it has three ptype.Property values detailed in Table 2.

   [TO BE REMOVED: The registry is currently accessible here:
   http://www.iana.org/assignments/email-auth/email-auth.xhtml \
                                                   #email-auth-methods ]

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

               Table 1: Method name, definition, and version

        +--------+----------+---------------------------+--------+
        | ptype  | Property | Value                     | Status |
        +--------+----------+---------------------------+--------+
        | dns    | zone     | The origin of the results | 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.

   [TO BE REMOVED: The registry is currently accessible here:
   http://www.iana.org/assignments/email-auth/email-auth.xhtml \
                                              #email-auth-result-names ]





Vesely                  Expires January 16, 2014                [Page 4]


Internet-Draft      DNSWL email-auth-method extension          July 2013


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

                          Table 3: Method results


4.  Implementation Status

   [Note to RFC Editor: please remove this entire section before
   publication.]

   This section records the status of a known implementation of the
   method described in this document at the time of writing, based on a
   proposal described in [I-D.sheffer-running-code].  See that document
   for further boilerplate.

   Courier-MTA is a full-featured, mature mail server, first publicly
   released in May 2000.  A beta release in February 2013 introduced
   Authentication-Results in combination with DNS-based whitelists.
   This document is based on that implementation, which made it to
   production release 0.71, after one month testing.  End-user
   documentation of that feature is available online at
   http://www.courier-mta.org/couriertcpd.html#idp5867072

   In prior releases, only the -block option was present, and the
   Authentication-Results header field was handled by add-ons, not by
   the core implementation.  The -allow option was added so that black
   and white lists can be configured using mostly symmetrical syntax.
   Finally, an option was added to inhibit SPF reject-on-fail for
   whitelisted senders.

   It is not possible to know how many installations of Courier-MTA have
   enabled these new features.  However, no questions have been asked
   about them on the mailing list, yet.  Despite the amount of spam,
   there seems to be little traction for this kind of development.

   The only DNSWL known to have been used for this purpose is dnswl.org.
   See http://www.dnswl.org/.  With nearly 150K entries, it can make the
   email messages that get at least one authentication "pass" overreach
   a critical mass: It seems that subscribing to that list is easier,
   for some mail admins, than implementing other authentication methods.




Vesely                  Expires January 16, 2014                [Page 5]


Internet-Draft      DNSWL email-auth-method extension          July 2013


5.  Security Considerations

   All of the considerations described in Section 8 of
   [I-D.ietf-appsawg-rfc5451bis] 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.


6.  References

6.1.  Normative References

   [I-D.ietf-appsawg-rfc5451bis]
              Kucherawy, M., "Message Header Field for Indicating
              Message Authentication Status",
              draft-ietf-appsawg-rfc5451bis-10 (work in progress),
              July 2013.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

6.2.  Informative References

   [I-D.sheffer-running-code]
              Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: the Implementation Status Section",
              draft-sheffer-running-code-06 (work in progress),
              June 2013.

   [RFC4408]  Wong, M. and W. Schlitt, "Sender Policy Framework (SPF)
              for Authorizing Use of Domains in E-Mail, Version 1",
              RFC 4408, April 2006.

   [RFC5518]  Hoffman, P., Levine, J., and A. Hathcock, "Vouch By
              Reference", RFC 5518, April 2009.

   [RFC5782]  Levine, J., "DNS Blacklists and Whitelists", RFC 5782,
              February 2010.

   [RFC6650]  Falk, J. and M. Kucherawy, "Creation and Use of Email
              Feedback Reports: An Applicability Statement for the Abuse
              Reporting Format (ARF)", RFC 6650, June 2012.



Vesely                  Expires January 16, 2014                [Page 6]


Internet-Draft      DNSWL email-auth-method extension          July 2013


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



































Vesely                  Expires January 16, 2014                [Page 7]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/