A Reputation Vocabulary for Email Identifiers
draft-ietf-repute-email-identifiers-02

REPUTE Working Group                                       N. Borenstein
Internet-Draft                                                  Mimecast
Intended status: Standards Track                            M. Kucherawy
Expires: July 16, 2012                                         Cloudmark
                                                        January 13, 2012

             A Reputation Vocabulary for Email Identifiers
                 draft-ietf-repute-email-identifiers-02

Abstract

   This document defines a vocabulary for describing assertions a
   reputation service provider can make about email identifers, for use
   with the application/reputon media type.

Status of this Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology and Definitions . . . . . . . . . . . . . . . . . . 3
     2.1.  Keywords  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     2.2.  Email Definitions . . . . . . . . . . . . . . . . . . . . . 3
     2.3.  Other Definitions . . . . . . . . . . . . . . . . . . . . . 3
   3.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  Assertions  . . . . . . . . . . . . . . . . . . . . . . . . 3
     3.2.  Vocabulary Extensions . . . . . . . . . . . . . . . . . . . 4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
     4.1.  Registration of 'email-id' Reputation Application . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . . . 6
   Appendix B.  Public Discussion  . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7

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1.  Introduction

   This memo specifies a vocabulary for describing reputation of an
   email identifier.  A "vocabulary" in this context is defined in
   [I-D.REPUTE-MODEL] and is used to describe assertions a reputation
   service provider can make about email identifiers as well as meta-
   data that can be included in such a reply beyond the base set
   specified there.

2.  Terminology and Definitions

   This section defines terms used in the rest of the document.

2.1.  Keywords

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [KEYWORDS].

2.2.  Email Definitions

   Commonly used definitions describing entities in the email
   architecture are defined and discussed in [EMAIL-ARCH].

2.3.  Other Definitions

   Other terms of importance in this memo are defined in
   [I-D.REPUTE-MODEL], the base memo in this document series.

3.  Discussion

   The expression of reputation about an email identifier requires
   extensions of the base set defined in [I-D.REPUTE-MODEL].  This memo
   defines and registers some common assertions about an entity found in
   a piece of [MAIL].

3.1.  Assertions

   The "email-id" reputation application recognizes the following
   assertions:

   FRAUD:  The subject identifier is associated with sending or handling
      of fraudulent email, such as "phishing" (some good discussion on
      this topic can be found in [IODEF-PHISHING])

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   MALWARE:  The subject identifier is associated with the sending or
      handling of malware via email

   SPAM:  The subject identifier is associated with sending or handling
      of unwanted bulk email

   INVALID-RECIPIENTS:  The subject identifier is associated with
      delivery attempts to nonexistent recipients

   For all assertions, the RATING scale is linear: A value of 0.0 means
   there is no data to support the assertion, a value of 1.0 means all
   accumulated data support the assertion, and the intervening values
   have a linear relationship (i.e., a score of "x" is twice as strong
   of an assertion as a value of "x/2").

3.2.  Vocabulary Extensions

   The "email-id" reputation application recognizes the following
   OPTIONAL extensions to the basic vocabulary defined in
   [I-D.REPUTE-MODEL]:

   IDENTITY:  A token indicating the source of the identifier; that is,
      where the subject identifier was found in the message.  This MUST
      be one of:

      DKIM:  The signing domain, i.e. the value of the "d=" tag, found
         on a valid [DKIM] signature in the message

      IPV4:  The IPv4 address of the client

      IPV6:  The IPv6 address of the client

      RFC5321.MAILFROM:  The RFC5321.MailFrom value of the envelope of a
         message of the message (see [SMTP])

      RFC5322.FROM:  The RFC5322.From field of the message (see [MAIL])

      SPF:  The domain name portion of the identifier (RFC5321.MailFrom
         or RFC5321.Helo) verified by [SPF])

   RATE:  A token that recommends an overall message acceptance rate for
      the subject domain.  This is expected to be a value tailored to
      the requesting agent; for example, the reputation service would
      use this to indicate that, based on the data reported by the
      requesting agent, the service recommends a particular message
      limit for that agent.  The value is an unsigned decimal value.

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   SOURCES:  A token relating a count of the number of sources of data
      that contributed to the reported reputation.  This is in contrast
      to the SAMPLE-SIZE parameter, which indicates the total number of
      reports across all reporting sources.

   A reply that does not contain the IDENTITY or SOURCES extensions is
   making a non-specific statement about how the reputation returned was
   developed.  A client may use or ignore such a reply at its
   discretion.

4.  IANA Considerations

   This memo presents one action for IANA, namely the registration of
   the reputation application "email-id".

4.1.  Registration of 'email-id' Reputation Application

   This section registers the "email-id" reputation application, as per
   the IANA Considerations section of [I-D.REPUTE-MODEL].  The
   registration parameters are as folows:

   o  Application name: email-id

   o  Short description: Evaluates DNS domain names found in email
      identifiers

   o  Defining document: [this memo]

   o  Status: current

   o  Application-specific query parameters:

      subject:  (current) specifies the subject of the reputation query;
         in this case, it is the email identifier whose reputation is
         requested

5.  Security Considerations

   This memo describes security considerations introduced by the
   reputation application and vocabulary defined here.

   [TBD]

6.  References

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6.1.  Normative References

   [DKIM]     Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
              "DomainKeys Identified Mail (DKIM) Signatures", RFC 6376,
              September 2011.

   [EMAIL-ARCH]
              Crocker, D., "Internet Mail Architecture", RFC 5598,
              July 2009.

   [I-D.REPUTE-MODEL]
              Borenstein, N. and M. Kucherawy, "A Model for Reputation
              Interchange", I-D draft-ietf-repute-model, November 2011.

   [KEYWORDS]
              Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

6.2.  Informative References

   [IODEF-PHISHING]
              Cain, P. and D. Jevans, "Extensions to the IODEF-Document
              Class for Reporting Phishing", RFC 5901, July 2010.

   [MAIL]     Resnick, P., Ed., "Internet Message Format", RFC 5322,
              October 2008.

   [SMTP]     Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              October 2008.

Appendix A.  Acknowledgments

   The authors wish to acknowledge the contributions of the following to
   this specification: Scott Kitterman, John Levine, S. Moonesamy, Doug
   Otis, and David F. Skoll.

Appendix B.  Public Discussion

   Public discussion of this suite of memos takes place on the
   domainrep@ietf.org mailing list.  See
   https://www.ietf.org/mailman/listinfo/domainrep.

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Authors' Addresses

   Nathaniel Borenstein
   Mimecast
   203 Crescent St., Suite 303
   Waltham, MA  02453
   USA

   Phone: +1 781 996 5340
   Email: nsb@guppylake.com

   Murray S. Kucherawy
   Cloudmark
   128 King St., 2nd Floor
   San Francisco, CA  94107
   USA

   Phone: +1 415 946 3800
   Email: msk@cloudmark.com

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