ON-DEMAND MAIL RELAY (ODMR) SMTP with Dynamic IP Addresses
RFC 2645

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Network Working Group                                        R. Gellens
Request for Comments: 2645                                     Qualcomm
Category: Standards Track                                   August 1999

                      ON-DEMAND MAIL RELAY (ODMR)
                    SMTP with Dynamic IP Addresses

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

Table of Contents

    1.  Abstract . . . . . . . . . . . . . . . . . . . . . . . . . .  1
    2.  Conventions Used in this Document . . . . . . . . . . . . . . 2
    3.  Comments . . . . . . . . . . . . . . . . . . . . . . . . . .  2
    4.  Description . . . . . . . . . . . . . . . . . . . . . . . . . 2
    5.  States . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
      5.1.  Initial State . . . . . . . . . . . . . . . . . . . . . . 4
        5.1.1.  EHLO . . . . . . . . . . . . . . . . . . . . . . . .  4
        5.1.2.  AUTH  . . . . . . . . . . . . . . . . . . . . . . . . 4
        5.1.3.  QUIT . . . . . . . . . . . . . . . . . . . . . . . .  4
      5.2.  Authenticated State . . . . . . . . . . . . . . . . . . . 4
        5.2.1.  ATRN (Authenticated TURN)  . . . . . . . . . . . . .  4
      5.3.  Reversed State  . . . . . . . . . . . . . . . . . . . . . 5
      5.4.  Other Commands . . . . . . . . . . . . . . . . . . . . .  6
    6.  Example On-Demand Mail Relay Session: . . . . . . . . . . . . 6
    7.  Response Codes . . . . . . . . . . . . . . . . . . . . . . .  6
    8.  Security Considerations . . . . . . . . . . . . . . . . . . . 6
    9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .  7
   10.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 7
   11.  Author's Address   . . . . . . . . . . . . . . . . . . . . .  8
   12.  Full Copyright Statement  . . . . . . . . . . . . . . . . . . 9

1.  Abstract

   With the spread of low-cost computer systems and Internet
   connectivity, the demand for local mail servers has been rising.
   Many people now want to operate a mail server on a system which has

Gellens                     Standards Track                     [Page 1]
RFC 2645                  On-Demand Mail Relay               August 1999

   only an intermittent connection to a service provider.  If the system
   has a static IP address, the ESMTP ETRN command [ETRN] can be used.
   However, systems with dynamic IP addresses (which are very common
   with low-cost connections) have no widely-deployed solution.

   This memo proposes a new service, On-Demand Mail Relay (ODMR), which
   is a profile of SMTP [SMTP, ESMTP], providing for a secure,
   extensible, easy to implement approach to the problem.

2.  Conventions Used in this Document

   Because the client and server roles reverse during the session, to
   avoid confusion, the terms "customer" and "provider" will be used in
   place of "client" and "server", although of course this protocol may
   be useful in cases other than commercial service providers and
   customers.

   In examples, "P:" is used to indicate lines sent by the provider, and
   "C:" indicates those sent by the customer.  Line breaks within a
   command are for editorial purposes only.

   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
   in this document are to be interpreted as defined in [KEYWORDS].

   Examples use 'example.net' as the provider, and 'example.org' and '
   example.com' as the customers.

3.  Comments

   Private comments should be sent to the author.  Public comments may
   be sent to the IETF Disconnected SMTP mailing list,
   <ietf-disconn-smtp@imc.org>.  To subscribe, send a message to
   <ietf-disconn-smtp-request@imc.org> containing the word SUBSCRIBE as
   the body.

4.  Description

   On-Demand Mail Relay is a restricted profile of SMTP [SMTP, ESMTP].
   Port 366 is reserved for On-Demand Mail Relay.  The initial client
   and server roles are short-lived, as the point is to allow the
   intermittently-connected host to request mail held for it by a
   service provider.

   The customer initiates a connection to the provider, authenticates,
   and requests its mail.  The roles of client and server then reverse,
   and normal SMTP [SMTP, ESMTP] proceeds.

Gellens                     Standards Track                     [Page 2]
RFC 2645                  On-Demand Mail Relay               August 1999

   The provider has an On-Demand Mail Relay process listening for
   connections on the ODMR port.  This process does not need to be a
   full SMTP server.  It does need to be an SMTP client with access to