Open Pluggable Edge Services (OPES) SMTP Use Cases
RFC 4496

Document Type RFC - Informational (May 2006; No errata)
Last updated 2013-03-02
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IESG IESG state RFC 4496 (Informational)
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Responsible AD Ted Hardie
Send notices to tony@att.com, tony+urireg@maillennium.att.com, hofmann@bell-labs.com
Network Working Group                                         M. Stecher
Request for Comments: 4496                              Secure Computing
Category: Informational                                        A. Barbir
                                                                  Nortel
                                                                May 2006

           Open Pluggable Edge Services (OPES) SMTP Use Cases

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   The Open Pluggable Edge Services (OPES) framework is application
   agnostic.  Application-specific adaptations extend that framework.
   This document describes OPES SMTP use cases and deployment scenarios
   in preparation for SMTP adaptation with OPES.

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................2
   3. Brief Overview of SMTP Architecture .............................3
      3.1. Operation Flow of an OPES SMTP System ......................4
           3.1.1. OPES SMTP Example ...................................5
   4. OPES/SMTP Use Cases .............................................6
      4.1. Security Filters Applied to Email Messages .................6
      4.2. Spam Filter ................................................7
      4.3. Logging and Reporting Filters ..............................8
      4.4. Access Control Filters .....................................8
      4.5. Secure Email Handling ......................................8
      4.6. Email Format Normalization .................................8
      4.7. Mail Rerouting and Address Rewriting .......................9
      4.8. Block Email during SMTP Dialog .............................9
      4.9. Convert Attachments to HTTP Links ..........................9
   5. Security Considerations ........................................10
   6. References .....................................................10
      6.1. Normative References ......................................10
      6.2. Informative References ....................................10
   Acknowledgements ..................................................11

Stecher & Barbir             Informational                      [Page 1]
RFC 4496                  OPES SMTP Use Cases                   May 2006

1.  Introduction

   The Open Pluggable Edge Services (OPES) architecture [1] enables
   cooperative application services (OPES services) between a data
   provider, a data consumer, and zero or more OPES processors.  The
   application services under consideration analyze and possibly
   transform application-level messages exchanged between the data
   provider and the data consumer.  The OPES processor can distribute
   the responsibility of service execution by communicating and
   collaborating with one or more remote callout servers.

   The execution of such services is governed by a set of rules
   installed on the OPES processor.  The rule evaluation can trigger the
   execution of service applications local to the OPES processor or on a
   remote callout server.

   Use cases for OPES based on HTTP [8] are described in [2].  This work
   focuses on OPES for SMTP [7] use cases, whereby additional use cases
   and enhancements to the types of OPES services defined in [2] are
   provided.

   In SMTP, the OPES processor may be any agent participating in SMTP
   exchanges, including a Mail Submission Agent (MSA), a Mail Transfer
   Agent (MTA), a Mail Delivery Agent (MDA), and a Mail User Agent
   (MUA).  This document focuses on use cases in which the OPES
   processor is a MTA.

   SMTP is a store-and-forward protocol.  Current email filtering
   systems either operate during the SMTP exchange or on messages that
   have already been received, after the SMTP connection has been closed
   (for example, in an MTA's message queue).

   This work focuses on SMTP-based services that want to modify command
   values or want to block SMTP commands.  In order to block a command,
   the service will provide an error message that the MTA should use in
   response to the command it received.  An OPES MTA will be involved in
   SMTP command modification and command satisfaction, analogous to
   request modification and request satisfaction from HTTP [8].

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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