One document matched: draft-ietf-marid-pra-00.txt

   MARID Working Group                                          J. Lyon
   Internet Draft                                        Microsoft Corp
   Document: draft-ietf-marid-pra-00.txt
   Expires: February 2005                                   August 2004


             Purported Responsible Address in E-Mail Messages


Status of this Memo

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Abstract

   The document defines an algorithm by which, given an e-mail message,
   one can extract the identity of the party that appears to have most
   proximately caused that message to be delivered.  This identity is
   called the "Purported Responsible Address" (PRA).













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Table of Contents

   1. Introduction...................................................2
   2. Determining the Purported Responsible Address..................3
   3. Security Considerations........................................4
   4. IANA Considerations............................................4
   5. Acknowledgements...............................................4
   6. References.....................................................4
      6.1 Normative References.......................................4
      6.2 Informative References.....................................5
   7. Author's Address...............................................5

Conventions used in this document

   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 [RFC2119].


1. Introduction

   Most E-Mail flows relatively directly from a sender to a recipient,
   with a small number of Mail Transfer Agents (MTAs) in between.  Some
   messages, however, are resent by forwarding agents, mailing list
   servers, and other such software.  These messages effectively result
   in two or more mail transactions: one from the sender to the
   forwarding agent, and another from the agent to the destination.

   In some cases, messages travel through more than one of these agents.
   This can occur, for example, when one mailing list is subscribed to
   another, or when the address subscribed to a mailing list is a
   forwarding service.

   Further complicating the situation, in some cases the party that
   introduces a message is not the author of the message.  For example,
   many news web sites have a "Mail this article" function that the
   public can use to e-mail a copy of the article to a friend.  In this
   case, the mail is "from" the person who pressed the button, but is
   physically sent by the operator of the web site.

   This document describes an algorithm that allows one to determine who
   appears to have most recently caused an e-mail message to be
   delivered.  It does this by inspecting the headers in the message.
   [RFC2822] contains a detailed specification of all of the relevant
   headers.

   Note that the results of this algorithm are only as truthful as the
   headers contained in the message; if a message contains fraudulent or
   incorrect headers, this algorithm will yield an incorrect result.


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   For this reason, the result of the algorithm is called the "Purported
   Responsible Address" -- "purported" because it tells you what a
   message claims about where it came from, but not necessarily where it
   actually came from.

   This document does not prescribe any particular uses for the
   Purported Responsible Address.  However, [SenderID] describes a
   method of determining whether a particular MTA is authorized to send
   mail on behalf of the domain contained in the PRA.


2. Determining the Purported Responsible Address

   The purported responsible address (PRA) of a message is determined by
   the following algorithm:

     1. Locate the first non-empty Resent-Sender header in the message.
        If no such header is found, continue with step 2.  If it is
        preceded by a non-empty Resent-From header and one or more
        Received or Return-Path headers occur after said Resent-From
        header and before the Resent-Sender header, continue with step
        2.  Otherwise, proceed to step 5.

     2. Locate the first non-empty Resent-From header in the message.
        If a Resent-From header is found, proceed to step 5. Otherwise,
        continue with step 3.

     3. Locate all the non-empty Sender headers in the message.  If
        there are no such headers, continue with step 4.  If there is
        exactly one such header, proceed to step 5.  If there is more
        than one such header, proceed to step 6.

     4. Locate all the non-empty From headers in the message.  If there
        is exactly one such header, continue with step 5.  Otherwise,
        proceed to step 6.

     5. A previous step has selected a single header from the message.
        If that header is malformed (e.g. it appears to contain multiple
        mailboxes, or the single mailbox is hopelessly malformed, or the
        single mailbox does not contain a domain name), continue with
        step 6.  Otherwise, return that single mailbox as the Purported
        Responsible Address.

     6. The message is ill-formed, and it is impossible to determine a
        Purported Responsible Address.


   Note that what constitutes a hopelessly malformed header or a
   hopelessly malformed mailbox in step 5 above is a matter for local


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   policy.  Such local policy will never cause two implementations to
   return different PRAs.  However it may cause one implementation to
   return a PRA where another implementation does not.  This will only
   occur when dealing with a message containing headers of questionable
   legality.

   Note that steps 1 and 2 above extract the Resent-Sender or Resent-
   From header from the first resent block (as defined by section 3.6.6
   of [RFC2822]) if any.  Steps 3 and 4 above extract the Sender or From
   header if there are no resent blocks.


3. Security Considerations

   The PRA, as described by this document, is extracted from message
   headers that have historically not been verified.  Thus, anyone using
   the PRA for any purpose MUST be aware that the headers from which is
   is derived might be fraudulent, malicious, malformed and/or
   incorrect.  [SenderID] describes one mechanism for validating the
   PRA.


4. IANA Considerations

   This document contains no actions for IANA.


5. Acknowledgements

   The PRA concept was first published in [CallerID].  It as been
   refined using valuable suggestions from members of the MARID working
   group.


6. References

6.1 Normative References

   [RFC2119]   S. Bradner, "Key words for use in RFCs to Indicate
               Requirement Levels", RFC 2119.

   [RFC2822]   P. Resnick (editor), "Internet Message Format", RFC 2822.









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6.2 Informative References

   [CallerID]  Microsoft Corporation, Caller ID for E-Mail Technical
               Specification,
               http://www.microsoft.com/mscorp/twc/privacy/spam_callerid
               .mspx.

   [SenderID]  J. Lyon and M. Wong, "Sender ID:  Authenticating E-Mail",
               draft-ietf-marid-core-03.  Work in progress.



7. Author's Address

   Jim Lyon
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA 98052
   USA
   jimlyon@microsoft.com


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   Copyright (C) The Internet Society (2004).  This document is subject
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   except as set forth therein, the authors retain all their rights.


Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




























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