IMAP Extension for STATUS=SIZE
RFC 8438

Document Type RFC - Proposed Standard (August 2018; No errata)
Last updated 2018-08-24
Replaces draft-bosch-imap-status-size
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Internet Engineering Task Force (IETF)                          S. Bosch
Request for Comments: 8438                                    Dovecot Oy
Category: Standards Track                                    August 2018
ISSN: 2070-1721

                     IMAP Extension for STATUS=SIZE

Abstract

   This document adds a new capability called "STATUS=SIZE" to the
   Internet Message Access Protocol (IMAP).  It allows retrieving the
   total storage size of a mailbox with a single STATUS command rather
   than retrieving and summing the sizes of all individual messages in
   that mailbox.

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 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/rfc8438.

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.  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.

Bosch                        Standards Track                    [Page 1]
RFC 8438               IMAP STATUS=SIZE Extension            August 2018

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   3.  STATUS Command and Response Extensions  . . . . . . . . . . .   3
   4.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   This document extends the Internet Message Access Protocol (IMAP)
   [IMAP4rev1] with a new capability called "STATUS=SIZE".  To determine
   the total storage size of a mailbox, an IMAP client currently needs
   to retrieve all message sizes individually using the FETCH command
   with the RFC822.SIZE data item.  The STATUS=SIZE capability provides
   a more efficient means of achieving this.  It extends the STATUS
   command with a new "SIZE" data item, which indicates the total size
   of all messages in the target mailbox.  This way, this information
   can be queried with just one STATUS command.  When the LIST-STATUS
   IMAP capability [LIST-STATUS] is also available, the SIZE data item
   can be queried for many mailboxes at once using just one LIST
   command.

   This capability is particularly useful for IMAP clients that do not
   cache the state of the message store, such as most webmail clients.
   Without the "STATUS=SIZE" capability, such clients need to fetch all
   message sizes from the server when the size of an individual mailbox
   needs to be determined.  For example, a user may request detailed
   quota usage information for each mailbox to find out which specific
   mailboxes consume most of the available storage resources.  Using
   this information, the user can get an overview of which mailboxes
   need to be cleaned up to reduce quota usage.  The QUOTA capability
   [QUOTA] is no help in that scenario, since the provided QUOTAROOT
   command can only yield the STORAGE resource usage of a whole quota
   root, not each individual mailbox within that root.

Bosch                        Standards Track                    [Page 2]
RFC 8438               IMAP STATUS=SIZE Extension            August 2018

2.  Conventions Used in This Document

   In examples, "C:" indicates lines sent by a client that is connected
   to a server.  "S:" indicates lines sent by the server to the client.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [KEYWORDS] [KEYWORDS2] when, and only when, they appear in all
   capitals, as shown here.
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