Internet Email to Support Diverse Service Environments (Lemonade) Profile
RFC 4550

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Network Working Group                                            S. Maes
Request for Comments: 4550                                        Oracle
Category: Standards Track                                    A. Melnikov
                                                              Isode Ltd.
                                                               June 2006

         Internet Email to Support Diverse Service Environments
                           (Lemonade) Profile

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 (2006).

Abstract

   This document describes a profile (a set of required extensions,
   restrictions, and usage modes) of the IMAP and mail submission
   protocols.  This profile allows clients (especially those that are
   constrained in memory, bandwidth, processing power, or other areas)
   to efficiently use IMAP and Submission to access and submit mail.
   This includes the ability to forward received mail without needing to
   download and upload the mail, to optimize submission, and to
   efficiently resynchronize in case of loss of connectivity with the
   server.

   The Internet Email to Support Diverse Service Environments (Lemonade)
   profile relies upon extensions to IMAP and Mail Submission protocols;
   specifically, the URLAUTH and CATENATE IMAP protocol (RFC 3501)
   extensions and the BURL extension to the SUBMIT protocol (RFC 4409).

Maes & Melnikov             Standards Track                     [Page 1]
RFC 4550                    Lemonade Profile                   June 2006

Table of Contents

   1. Introduction ....................................................3
      1.1. Conventions Used in This Document ..........................3
   2. Forward without Download ........................................3
      2.1. Motivations ................................................3
      2.2. Message Sending Overview ...................................4
      2.3. Traditional Strategy .......................................4
      2.4. Step-by-Step Description ...................................5
           2.4.1. Message Assembly Using IMAP CATENATE Extension ......6
           2.4.2. Message Assembly Using SMTP CHUNKING and
                  BURL Extensions ....................................10
      2.5. Normative Statements Related to Forward without Download ..14
      2.6. Security Considerations for "pawn-tickets" ................14
      2.7. The fcc Problem ...........................................15
      2.8. Registration of $Forwarded IMAP Keyword ...................15
   3. Message Submission .............................................15
      3.1. Pipelining ................................................16
      3.2. DSN Support ...............................................16
      3.3. Message Size Declaration ..................................16
      3.4. Enhanced Status Code Support ..............................16
      3.5. TLS .......................................................16
   4. Quick Resynchronization ........................................16
   5. Additional IMAP Extensions .....................................17
   6. Summary of the Required IMAP and SMTP Extensions ...............17
   7. Future work ....................................................18
   8. Security Considerations ........................................18
      8.1. Confidentiality Protection of Submitted Messages ..........19
      8.2. TLS .......................................................19
   9. References .....................................................20
      9.1. Normative References ......................................20
      9.2. Informative References ....................................21
   10. Acknowledgements ..............................................21

Maes & Melnikov             Standards Track                     [Page 2]
RFC 4550                    Lemonade Profile                   June 2006

1.  Introduction

   Lemonade provides enhancements to Internet email to support diverse
   service environments.

   This document describes the Lemonade profile, which includes:

      -  "forward without download", which describes exchanges between
         Lemonade clients and servers to allow new email messages to be
         submitted incorporating content that resides on locations
         external to the client.

      -  Quick mailbox resynchronization using [CONDSTORE].

      -  Several IMAP and SMTP extensions that save bandwidth and/or
         number of round-trips required to send/receive data.

   The organization of this document is as follows.  Section 2 describes