The IMAP APPENDLIMIT Extension
RFC 7889
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
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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]
RFC 7889 The IMAP APPENDLIMIT Extension May 2016
2. APPENDLIMIT Extension
An IMAP server that supports the APPENDLIMIT extension advertises
this by including the name APPENDLIMIT in its capability list in the
authenticated state. The server may also advertise this extension
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