The IMAP APPENDLIMIT Extension
RFC 7889

Document Type RFC - Proposed Standard (May 2016; No errata)
Last updated 2016-05-17
Replaces draft-jayantheesh-imap-appendlimit-extension
Stream IETF
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Stream WG state Submitted to IESG for Publication
Document shepherd S Moonesamy
Shepherd write-up Show (last changed 2015-12-07)
IESG IESG state RFC 7889 (Proposed Standard)
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Responsible AD Barry Leiba
Send notices to "S Moonesamy" <sm+ietf@elandsys.com>
IANA IANA review state Version Changed - Review Needed
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Internet Engineering Task Force (IETF)    J. SrimushnamBoovaraghamoorthy
Request for Comments: 7889                                      N. Bisht
Category: Standards Track                    Samsung Electronics America
ISSN: 2070-1721                                                 May 2016

                     The IMAP APPENDLIMIT Extension

Abstract

   This document defines an extension to the IMAP service whereby a
   server can inform the client about maximum message upload sizes,
   allowing the client to avoid sending APPEND commands that will fail
   because the messages are too large.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7889.

Copyright Notice

   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
   Provisions Relating to IETF Documents
   (http://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.  Code Components extracted from this document must
   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.

SrimushnamB. & Bisht         Standards Track                    [Page 1]
RFC 7889             The IMAP APPENDLIMIT Extension             May 2016

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  APPENDLIMIT Extension . . . . . . . . . . . . . . . . . . . .   3
   3.  Mailbox-Specific APPENDLIMIT  . . . . . . . . . . . . . . . .   3
     3.1.  STATUS Response to the STATUS Command . . . . . . . . . .   4
     3.2.  STATUS Response to the LIST Command . . . . . . . . . . .   4
     3.3.  APPENDLIMIT Behavior  . . . . . . . . . . . . . . . . . .   4
   4.  APPEND Response . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Some IMAP servers have limits for message upload size, and those
   limits are not published to the email client.  When the email client
   APPENDs a message with huge attachments, using non-synchronizing
   literals, the APPEND fails because of the upload limit, but the
   client has already sent the message data anyway.  This results in
   unnecessary resource usage.  Especially in the mobile device
   environment, appending a message with huge attachments consumes
   device resources like device battery power and mobile data.

   The IMAP APPENDLIMIT extension provides the ability to advertise a
   maximum upload size allowed by the IMAP server, so that the email
   client knows the size limitation beforehand.  By implementing this
   extension, IMAP server-side processing of huge attachments above the
   maximum upload size can be avoided.

1.1.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   In examples, "C:" and "S:" indicate lines sent by the client and
   server, respectively.  If a single "C:" or "S:" label applies to
   multiple lines, then the line breaks between those lines are for
   editorial clarity only and are not part of the actual protocol
   exchange.

SrimushnamB. & Bisht         Standards Track                    [Page 2]
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