Multicast Email (MULE) over Allied Communications Publication (ACP) 142
RFC 8494

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Independent Submission                                         D. Wilson
Request for Comments: 8494                              A. Melnikov, Ed.
Category: Informational                                        Isode Ltd
ISSN: 2070-1721                                            November 2018

Multicast Email (MULE) over Allied Communications Publication (ACP) 142

Abstract

   Allied Communications Publication (ACP) 142 defines P_MUL, which is a
   protocol for reliable multicast suitable for bandwidth-constrained
   and delayed acknowledgement (Emissions Control or "EMCON")
   environments running over UDP.  This document defines MULE (Multicast
   Email), an application protocol for transferring Internet Mail
   messages (as described in RFC 5322) over P_MUL (as defined in ACP
   142).  MULE enables transfer between Message Transfer Agents (MTAs).
   It doesn't provide a service similar to SMTP Submission (as described
   in RFC 6409).

   This document explains how MULE can be used in conjunction with SMTP
   (RFC 5321), including some common SMTP extensions, to provide an
   alternate MTA-to-MTA transfer mechanism.

   This is not an IETF specification; it describes an existing
   implementation.  It is provided in order to facilitate interoperable
   implementations and third-party diagnostics.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not candidates for any level of Internet Standard;
   see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8494.

Wilson & Melnikov             Informational                     [Page 1]
RFC 8494                   Email over ACP 142              November 2018

Copyright Notice

   Copyright (c) 2018 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
   (https://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.

Table of Contents

   1. Introduction ....................................................3
   2. Conventions Used in This Document ...............................4
   3. MULE ............................................................4
      3.1. BSMTP-Like Payload Construction ............................6
      3.2. Payload Compression ........................................7
      3.3. Error Handling .............................................9
   4. Gatewaying from Internet Mail to MULE ...........................9
      4.1. Use of BDAT ...............................................10
   5. Gatewaying from MULE to Internet Mail ..........................10
      5.1. Handling of ESMTP Extensions and Errors ...................10
   6. IANA Considerations ............................................11
      6.1. Instructions for Designated Experts .......................11
      6.2. SMTP Extension Support in MULE ............................12
   7. Security Considerations ........................................14
   8. References .....................................................15
      8.1. Normative References ......................................15
      8.2. Informative References ....................................17
   Acknowledgements ..................................................19
   Authors' Addresses ................................................19

Wilson & Melnikov             Informational                     [Page 2]
RFC 8494                   Email over ACP 142              November 2018

1.  Introduction

   P_MUL [ACP142A] is a transport protocol for reliable multicast in
   bandwidth-constrained and delayed acknowledgement environments
   running on top of UDP.  This document defines MULE, an application
   protocol for transferring Internet Mail messages [RFC5322] over ACP
   142 P_MUL.  The objectives of MULE are 1) to take advantage of the
   bandwidth-saving feature of using the multicast service as supported
   by modern computer networks and 2) to allow message transfer under
   EMCON (Emissions Control) conditions.  EMCON or "radio silence" means
   that although receiving nodes are able to receive messages, they are
   not able to acknowledge the receipt of messages.

   The objective of this protocol is to take advantage of multicast
   communication for the transfer of messages between MTAs (Message