SMTP Service Extension for Client Identity
draft-storey-smtp-client-id-04

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Last updated 2017-07-31
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INTERNET-DRAFT                                                 W. Storey
<draft-storey-smtp-client-id-04.txt>                          LinuxMagic
Intended Status: Standards Track
Expires February 1, 2018                                  August 1, 2017

               SMTP Service Extension for Client Identity
                  <draft-storey-smtp-client-id-04.txt>

Abstract

   This document defines an extension for the Simple Mail Transfer
   Protocol (SMTP) called "CID" to provide a method for clients to
   indicate an identity to the server.

   This identity is an additional token that may be used for security
   and/or informational purposes, and with it a server may optionally
   apply heuristics using this token.

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
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Copyright Notice

   Copyright (c) 2016 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

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INTERNET-DRAFT            SMTP Client Identity            August 1, 2017

   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.

Storey, William          Expires February 1, 2018               [Page 2]
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Table of Contents

   1.  Introduction ...................................................3
   2.  The CID Service Extension ......................................4
   3.  The CID Keyword of the EHLO Command ............................4
   4.  The CID Command ................................................5
   5.  Formal Syntax ..................................................6
   6.  Discussion .....................................................7
       6.1 Utility ....................................................7
       6.2 Use Cases ..................................................7
       6.3 Other SMTP Identities ......................................8
   7.  Client Identity Types ..........................................8
   8.  Examples .......................................................9
       8.1 MAC Address as Client Identity .............................9
       8.2 Client Identity Without a TLS/SSL Session ..................9
       8.3 Client Identity Leading to Rejection ......................10
       8.4 Malformed CID Command .....................................10
   9.  Security Considerations .......................................11
   10. IANA Considerations ...........................................11
       10.1 SMTP Extension Registration ..............................11
   11. References ....................................................11
       11.1 Normative References .....................................11

1. Introduction

   The [SMTP] protocol and its extensions describe methods whereby an
   SMTP client may provide identity information to an SMTP server.
   However, every exisitng method for providing an identity is subject
   to limitations, and none offer a way to identify the SMTP client with
   absolute confidence.  This document defines an additional method to
   provide an identity that represents the SMTP client with a higher
   degree of confidence when accessing the SMTP server.

   Typically SMTP clients are identified by establishing an authorized
   connection using the [AUTH] SMTP extension.  SMTP servers are often
   subject to malicious clients attempting to use authorized identities
   not intended for their use (often referred to as a brute- force
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