Sieve Email Filtering: Delivering to Special-Use Mailboxes
RFC 8579

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Internet Engineering Task Force (IETF)                          S. Bosch
Request for Comments: 8579                               Open Xchange Oy
Category: Standards Track                                       May 2019
ISSN: 2070-1721

       Sieve Email Filtering: Delivering to Special-Use Mailboxes

Abstract

   The SPECIAL-USE capability of the IMAP protocol (RFC 6154) allows
   clients to identify special-use mailboxes, e.g., where draft or sent
   messages should be put.  This simplifies client configuration.  In
   contrast, the Sieve mail filtering language (RFC 5228) currently has
   no such capability.  This memo defines a Sieve extension that fills
   this gap: it adds a test for checking whether a special-use attribute
   is assigned for a particular mailbox or any mailbox, and it adds the
   ability to file messages into a mailbox identified solely by a
   special-use attribute.

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/rfc8579.

Copyright Notice

   Copyright (c) 2019 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
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   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Bosch                        Standards Track                    [Page 1]
RFC 8579              Sieve: Special-Use Mailboxes              May 2019

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   3.  Test "specialuse_exists"  . . . . . . . . . . . . . . . . . .   3
     3.1.  Equivalent IMAP Operations  . . . . . . . . . . . . . . .   4
   4.  ":specialuse" Argument to "fileinto" Command  . . . . . . . .   5
     4.1.  Mailboxes Created Implicitly by the "fileinto" Command  .   6
     4.2.  Equivalent IMAP Operations  . . . . . . . . . . . . . . .   7
   5.  Sieve Capability Strings  . . . . . . . . . . . . . . . . . .   8
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Commonly, several mailboxes in an IMAP message store [IMAP] have a
   special use.  For example, there can be a special-use mailbox for
   storing the user's draft messages, for keeping copies of sent
   messages, and for collecting spam messages that were classified as
   such at delivery.  The SPECIAL-USE capability [SPECIAL-USE] of the
   IMAP protocol defines mailbox attributes that identify these special
   mailboxes explicitly to the client.  This way, client configuration
   is simplified significantly.  Using the CREATE-SPECIAL-USE capability
   [SPECIAL-USE], IMAP clients can also configure these attributes
   dynamically based on user preference.

   Unlike the IMAP protocol, the Sieve mail filtering language [SIEVE]
   currently cannot freely access these special-use mailbox attributes.
   Particularly, the Sieve interpreter has no means to identify a
   mailbox with a particular special-use attribute.  This would be very
   useful, for example, to find the user's "Spam" mailbox at delivery.

   In Sieve, limited access to the special-use attributes is provided
   using the "mboxmetadata" extension [SIEVE-MAILBOX], which allows
   testing for the presence of a special-use attribute in the "/private/
   specialuse" IMAP METADATA [IMAP-METADATA] entry of a mailbox.  Still,
   not all implementers will be willing to add the complexity of the
   IMAP METADATA capability just to provide access to special-use
   attributes to the Sieve interpreter.