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Network Working Group                                        A. Hathcock
Internet-Draft                                                 J. Merkel
Intended Status: Informational                        Alt-N Technologies
Expires: September 6, 2007                                 March 6, 2007


              The Minger Email Address Verification Protocol
                       draft-hathcock-minger-00.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on September 6, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document describes the Minger protocol.  Minger is a protocol
   for determining whether an email address exists and, optionally,
   retrieving some basic information about the user of that address.
   It includes security in the form of a username/password combination
   but can also be used anonymously if desired.

Requirements Language

   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].


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Table of Contents

   1       Introduction . . . . . . . . . . . . . . . . . . . . . . .  3
   1.1     The problem  . . . . . . . . . . . . . . . . . . . . . . .  3
   1.2     Existing solutions . . . . . . . . . . . . . . . . . . . .  3
   1.2.1   Finger . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.2.2   SMTP "call-back" / "call-forward"  . . . . . . . . . . . .  3
   1.3     The solution . . . . . . . . . . . . . . . . . . . . . . .  4
   2.      The Minger protocol  . . . . . . . . . . . . . . . . . . .  4
   2.1     The Minger query process . . . . . . . . . . . . . . . . .  4
   2.2     Minger responses . . . . . . . . . . . . . . . . . . . . .  5
   2.2.1   Example responses  . . . . . . . . . . . . . . . . . . . .  5
   3.      Anonymous mode . . . . . . . . . . . . . . . . . . . . . .  6
   4.      Security Considerations  . . . . . . . . . . . . . . . . .  7
   5.      IANA Considerations  . . . . . . . . . . . . . . . . . . .  7
   6.      Informative References . . . . . . . . . . . . . . . . . .  8

   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  9
   Intellectual Property and Copyright Statements . . . . . . . . . . 10

































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1.  Introduction

1.1 The problem

   It is common for elements within a typical email handling topology
   to be unaware of whether individual local-parts are valid for the
   mail it accepts.  For example, so-called "edge" servers which provide
   security oriented services for downstream mail handling elements
   often do not have an exhaustive listing of all valid local-parts for
   a given domain.  Thus, they are sometimes forced to accept messages
   which might otherwise be rejected as "user unknown".  Similarly,
   entities offering "backup MX" mail services are rarely privy to a
   complete local-part listing and are therefore forced to accept
   messages which might otherwise be rejected.  Finally, even within a
   common administrative framework of several locally maintained and
   controlled SMTP servers in a load balanced configuration, it is not
   always possible for all servers to access a common local-part
   database.

1.2 Existing solutions

   The need to determine whether an email address contains a valid local
   part has lead to the use of at least two existing mechanisms - Finger
   [RFC1288] and SMTP "call-back" / "call-forward".

1.2.1 Finger

   Finger [RFC1288] describes a protocol for the exchange of user
   information.  In theory, Finger could be used to determine whether an
   account exists by careful examination of the results of a Finger
   query.  However, Finger suffers from a lack of security which makes
   its modern day use problematic.  For example, it is possible for
   attackers to obtain information about the users of an email system
   which they can then sell or use as targets for spam and viruses.
   Also, Finger requires the use of TCP rather than UDP which seems ill
   suited to a simple verification scheme.

1.2.2 SMTP "call-back" / "call-forward"

   These terms are used to describe a widespread practice whereby SMTP
   servers place an incoming SMTP session on hold while they attempt to
   use an outbound SMTP session to determine whether or not a given
   email address is valid.  The theory behind this is as follows:  if an
   SMTP server responds positively to an SMTP RCPT or MAIL command
   [RFC2821] with a given email address then this potentially means that
   the address local part is valid.  One problem with such a scheme is
   the lack of efficiency inherent in the need to tear-up and tear-down
   an SMTP session over TCP.  Also, because these types of SMTP sessions
   are not purposed to deliver mail, they typically drop connection
   after the RCPT command is processed.  This leads to a large number of
   SMTP sessions which appear in logs to have simply failed for no
   reason.

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1.3 The solution

   What's needed is a UDP based protocol which is secure, has little
   overhead, and can be easily invoked to determine whether a given
   email address is valid or not.  Minger fulfills this need.


2.  The Minger protocol

   Minger is a UDP protocol that operates on port 49152.

     Editor's note:  The authors have applied to IANA for a
     registered port.  Until then, implementations will test
     using the above private port.

   Syntax descriptions use the form described in Augmented Backus-Naur
   Form for Syntax Specifications (ABNF) [RFC4234].

2.1  The Minger query process

   A Minger client constructs a query string comprised of either two or
   four elements and transmits it over UDP to a Minger server.  The
   format of the query is as follows:

  ABNF:

    Query string = id SP mailbox [SP username SP password]

    id = 1 * 50(VCHAR)                ; used to match a query to a
                                      ; response

    mailbox = Local-part "@" Domain   ; as defined in RFC2821

    username = 1 * 50(VCHAR)          ; optional username for security

    password = 1 * 50(VCHAR)          ; optional password for security

  id - This is a randomly generated value which Minger clients include
       in each query.  This same value will be echoed back in the
       response returned by the Minger server and can therefore be used
       to match responses with the proper query.

  mailbox - This is the email address for which verification of
       existence is desired.

  username and password - These values are pre-arranged elements
       determined and configured in advance so that Minger servers
       provide service only to authorized clients.  When not provided,
       Minger is operating in anonymous mode.




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2.2  Minger responses

   Minger servers return responses in a simple XML format.  Despite the
   overhead of including XML tags within the limited space available
   with UDP, XML allows for very easy parsing by the receiving client
   and the data returned would rarely approach the UDP space limit.  The
   XML format returned by the Minger server has certain required
   elements but can include other elements as desired by particular
   implementations.

  ABNF:

    Response = "<MingerResponse>" minger-data "</MingerResponse>"

    Minger-data = "<ID>" id "</ID>" (status user-data / error)

    id = 1 * 50(VCHAR)           ; id of the query being responded to

    status = "<Status>" ("Active" / "Not found" / "Disabled" /
              1*(ALPHA / DIGIT)) "</Status>"

    error = "<Error>" 1 * (ALPHA / DIGIT) "</Error>"

    user-data = *("<" tag-name ">" 1 * (VCHAR) "</" tag-name ">")

    tag-name = 1 * (VCHAR)


   Minger servers MUST support "status" values of "active", "not found",
   and "disabled".

   Minger servers MAY return additional XML nodes containing data not
   defined in this specification.


2.2.1  Example responses


  A.  Minger response when email address "not found" (returned when the
      queried email address does not exist):

      <MingerResponse>
      <ID>12345</ID>
      <Status>not found</Status>
      </MingerResponse>








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  B.  Minger response for error conditions (in this case, invalid
      credentials):

      <MingerResponse>
      <ID>54321</ID>
      <Error>bad username or password</Error>
      </MingerResponse>

  C.  Minger response for "active" email addresses (returned when the
      queried email address exists and is ready to receive mail):

      <MingerResponse>
      <ID>abc123def</ID>
      <Status>Active</Status>
      </MingerResponse>

  D.  Minger response returning optional extra data:

      <MingerResponse>
      <ID>gfs54ad4fs</ID>
      <Status>Active</Status>
      <FullName>Arvel Hathcock</FullName>
      <Email>arvel@altn.com</Email>
      </MingerResponse>



3.  Anonymous mode

   Minger clients MAY attempt anonymous queries; that is, queries which
   do not contain a username or password within the query string.
   Minger servers SHOULD respond to anonymous queries in the same way
   they respond to authenticated queries.  However, Minger servers MAY
   be configured to refuse anonymous queries.  If so, they MUST respond
   with an error as described above.  Additionally, Minger responses to
   anonymous queries may contain a sub-set or none of the optional extra
   XML data that would otherwise be present.  However, any response must
   meet the minimums required by this specification.















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4.  Security Considerations

   Minger is used to obtain information about the validity of an email
   address.  It can also be used to retrieve implementation specific
   "extra" data about the user of an email address.  Minger include a
   username/password concept to prevent unauthorized use.  However, it
   also supports an anonymous mode in which use of these credentials may
   not be required.  It's conceivable that the use of anonymous mode or
   the compromise of authentication credentials could lead to the
   undesired provision of information which could then be used for
   nefarious purposes.  Care must be taken to secure the credentials
   used by Minger and to police the provision of information when using
   anonymous mode.


5.  IANA Considerations

   Minger requires allocation of a Registered Port by IANA.



































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6.  Informative References

   [RFC1288]  Zimmerman, D., "The Finger User Information Protocol",
              RFC 1288, December 1991.

   [RFC2821]  Klensin, J., Editor, "Simple Mail Transfer Protocol", RFC
              2821, March 2001.

   [RFC4234]  Crocker, D., Ed. And P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 4234, October 2005.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.








































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Appendix A.  Acknowledgements

  We wish to thank the members of the MDaemon Beta Community
  (subscribe-md-beta@altn.com) for their ideas and help.


Authors' Addresses

   Arvel Hathcock
   Alt-N Technologies
   http://www.altn.com

   Email: arvel.hathcock@altn.com


   Jonathan Merkel
   Alt-N Technologies
   http://www.altn.com

   Email: jon.merkel@altn.com

































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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

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