SMTP Service Extension for Client Identity
draft-storey-smtp-client-id-07

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Last updated 2019-06-07
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INTERNET-DRAFT                                                 W. Storey
<draft-storey-smtp-client-id-07.txt>                          LinuxMagic
Intended Status: Standards Track
Expires December 6, 2019                                    June 6, 2019

               SMTP Service Extension for Client Identity
                  <draft-storey-smtp-client-id-07.txt>

Abstract

   This document defines an extension for the Simple Mail Transfer
   Protocol (SMTP) called "CLIENTID" 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

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   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
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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must

Storey, William         Expires December 6, 2019                [Page 1]
INTERNET-DRAFT            SMTP Client Identity              June 6, 2019

   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 December 6, 2019                [Page 2]
INTERNET-DRAFT            SMTP Client Identity              June 6, 2019

Table of Contents

   1.  Introduction .................................................  3
   2.  The CLIENTID Service Extension ...............................  4
   3.  The CLIENTID Keyword of the EHLO Command .....................  4
   4.  The CLIENTID Command .........................................  5
   5.  Formal Syntax ................................................  5
   6.  Discussion ...................................................  6
       6.1. Applying heuristics to CLIENTID .........................  6
       6.2. Utility of CLIENTID .....................................  6
       6.3. Use Cases of CLIENTID ...................................  7
       6.4. Other SMTP Client Identifiers ...........................  9
       6.5. Future Considerations ...................................  9
   7.  Client Identity Types ........................................  9
   8.  Examples ..................................................... 11
       8.1 UUID Address as Client Identity .......................... 11
       8.2 Client Identity Without a TLS/SSL Session ................ 12
       8.3 Client Identity Leading to Rejection ..................... 12
       8.4 Malformed CLIENTID Command ............................... 13
   9.  Security Considerations ...................................... 13
   10. IANA Considerations .......................................... 14
       10.1 SMTP Extension Registration ............................. 14
   11. References ................................................... 14
       11.1 Normative References .................................... 14

1. Introduction

   The [SMTP] protocol and its extensions describe methods whereby an
   SMTP client may provide identity and/or authentication information to
   an SMTP server.  However, these existing methods are subject to
   limitations and none offer a way to identify the SMTP client with
   absolute confidence.  This document defines an SMTP service extension
   to provide an additional identity token which can represent the SMTP
   client with a higher degree of certainty 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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