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EXTRA                                                       K. Murchison
Internet-Draft                                                 R. Signes
Updates: 5232 (if approved)                                   N. Jenkins
Intended status: Standards Track                                Fastmail
Expires: February 8, 2021                                 August 7, 2020


                Sieve Email Filtering: Snooze Extension
                    draft-ietf-extra-sieve-snooze-00

Abstract

   This document describes the "snooze" extension to the Sieve email
   filtering language.  The "snooze" extension gives Sieve the ability
   to postpone the filing of an incoming into a target mailbox until a
   later point in time.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 8, 2021.

Copyright Notice

   Copyright (c) 2020 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.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   3.  Snooze Action . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Mailbox Argument  . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Weekdays Argument . . . . . . . . . . . . . . . . . . . .   4
     3.3.  Times and TZID Arguments  . . . . . . . . . . . . . . . .   4
       3.3.1.  Awaken Times Examples . . . . . . . . . . . . . . . .   4
     3.4.  Interaction with Extensions to the Fileinto Action  . . .   5
       3.4.1.  Imap4flags Extension  . . . . . . . . . . . . . . . .   6
       3.4.2.  Mailbox Extension . . . . . . . . . . . . . . . . . .   6
       3.4.3.  Special-Use Extension . . . . . . . . . . . . . . . .   7
       3.4.4.  MailboxID Extension . . . . . . . . . . . . . . . . .   7
   4.  Mechanics of Snoozing Messages  . . . . . . . . . . . . . . .   7
     4.1.  SMTP Future Message Release . . . . . . . . . . . . . . .   8
     4.2.  "Snoozed" Mailbox . . . . . . . . . . . . . . . . . . . .   8
   5.  Implementation Status . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Registration of Sieve Extension . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11
     9.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Users are not always ready, willing, or able to read and respond to
   email messages at the time of their arrival.  Sometimes it is
   desirable to have messages appear in a mailbox at a more convenient
   time for the user to act upon them.

   This document defines a new Sieve action command "snooze" that
   postpones filing a message into a target mailbox until a later point
   in time.  The capability string associated with this extension is
   "snooze".

2.  Conventions Used in This Document

   Conventions for notations are as in Section 1.1 of [RFC5228],
   including use of the "Usage:" label for the definition of action and
   tagged arguments syntax.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and



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   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Snooze Action

   Usage: snooze *AWAKEN-OPTIONS <times: string-list>

   The AWAKEN-OPTIONS argument is defined here in ABNF [RFC4234] syntax
   so that it can be modified by other extensions.

   AWAKEN-OPTIONS = MAILBOX / WEEKDAYS / TZID
                     ; each option MUST NOT appear more than once
                     ; however, per Section 2.6.2 of RFC 5228,
                     ; the tagged arguments in AWAKEN-OPTIONS
                     ; may appear in any order

   MAILBOX  = ":mailbox" string
   WEEKDAYS = ":weekdays" string-list
   TZID     = ":tzid" string

   The snooze action is semantically equivalent to a delayed fileinto
   action (see Section 4.1 of [RFC5228]).  The arguments of the snooze
   action specify when, where, and how the awakened message will be
   filed.

   The process of actually snoozing and awakening (delaying the filing
   of) the message is implementation specific and outside the scope of
   this document.  However, Section 4 discusses possible methods for
   implementing the snooze action.

3.1.  Mailbox Argument

   The optional :mailbox argument is used to specify the target mailbox
   that the message will be filed into when it is awakened.  It is
   equivalent to the mailbox argument of the fileinto action (see
   Section 4.1 of [RFC5228]).

   If :mailbox is omitted, or if the specified mailbox doesn't exist at
   the time of awakening, the message will be filed into the user's main
   mailbox.  For instance, in an implementation where the IMAP server is
   running scripts on behalf of the user at time of delivery, the user's
   "INBOX" would be the implicit target for awakening messages.








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3.2.  Weekdays Argument

   The optional :weekdays argument specifies the set of days on which
   the specified set of awakening times apply.  Each day of the week is
   expressed as an integer between "0" and "6". "0" is Sunday, "1" is
   Monday, etc.  This syntax matches that of the "weekday" date-part
   argument to the date test extension (see Section 4.2 of [RFC5260]).

   If :weekdays is omitted, the set of awakening times applies to every
   day of the week.

3.3.  Times and TZID Arguments

   The required times argument, along with the optional :tzid argument,
   are used to specify when a snoozed message will be awakened.  Each
   time is specified in "hh:mm:ss" format and is interpreted as the
   local time in the time zone specified by the :tzid argument.

   The value of the :tzid argument MUST be a time zone identifier from
   the IANA Time Zone Database [tzdb].  If :tzid is omitted, the time
   zone of the Sieve interpreter is used.

   The combination of the weekdays and times form a chronological list
   of awaken times.  When a message is snoozed, it is assigned the next
   future awaken time in the list.  If a message is snoozed on a day
   with no awaken times, or after the last awaken time on a given day,
   the first awaken time on the next available day is used.

   If the local time in the specified time zone occurs more than once
   (daylight saving to standard time transition), the first occurrence
   of the specified time value is used.  If the local time in the
   specified time zone does not occur (standard to daylight saving time
   transition), the specified time value is interpreted using the UTC
   offset prior to the transition.

3.3.1.  Awaken Times Examples

   The following examples show, given the specified snooze action and a
   set of message arrival times, the corresponding times at which the
   message would be awakened and filed.

   The following example shows awaken times rolling into the next day or
   week.  Note that 2020-07-30 falls on a Thursday.

   require "snooze";
   snooze :weekdays ["1", "3", "5", "2", "4"]
          :tzid "Australia/Melbourne" ["12:00:00",
                                       "08:00:00", "16:00:00"];



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   +----------------------+---------------------+---------------------+
   |    Arrival (UTC)     | Arrival (Melbourne) |  Awaken (Melbourne) |
   +----------------------+---------------------+---------------------+
   | 2020-07-30T00:00:00Z | --07-30T10:00:00+10 | --07-30T12:00:00+10 |
   | 2020-07-30T04:00:00Z | --07-30T14:00:00+10 | --07-30T16:00:00+10 |
   | 2020-07-30T08:00:00Z | --07-30T18:00:00+10 | --07-31T08:00:00+10 |
   | 2020-07-31T12:00:00Z | --07-31T22:00:00+10 | --08-03T08:00:00+10 |
   | 2020-08-01T16:00:00Z | --08-02T02:00:00+10 | --08-03T08:00:00+10 |
   +----------------------+---------------------+---------------------+

   The following example shows awaken times falling before, during, and
   after a daylight saving to standard time transition.  Note that the
   transition occurs at 2020-11-01T02:00:00-04.

   require "snooze";
   snooze :tzid "America/New_York" "01:30:00";

   +----------------------+---------------------+---------------------+
   |    Arrival (UTC)     |  Arrival (New York) |  Awaken (New York)  |
   +----------------------+---------------------+---------------------+
   | 2020-11-01T05:00:00Z | --11-01T01:00:00-04 | --11-01T01:30:00-04 |
   | 2020-11-01T06:00:00Z | --11-01T01:00:00-05 | --11-02T01:30:00-05 |
   | 2020-11-01T07:00:00Z | --11-01T02:00:00-05 | --11-02T01:30:00-05 |
   +----------------------+---------------------+---------------------+

   The following example shows awaken times falling before, during, and
   after a standard to daylight saving time transition.  Note that the
   transition occurs at 2021-03-14T02:00:00-05.

   require "snooze";
   snooze :tzid "America/New_York" "02:30:00";

   +----------------------+---------------------+---------------------+
   |    Arrival (UTC)     |  Arrival (New York) |  Awaken (New York)  |
   +----------------------+---------------------+---------------------+
   | 2021-03-13T06:30:00Z | --03-13T01:30:00-05 | --03-13T02:30:00-05 |
   | 2021-03-14T06:30:00Z | --03-14T01:30:00-05 | --03-14T03:30:00-04 |
   | 2021-03-14T07:30:00Z | --03-14T03:30:00-04 | --03-15T02:30:00-04 |
   +----------------------+---------------------+---------------------+

3.4.  Interaction with Extensions to the Fileinto Action

   Some tagged arguments defined in extensions to the fileinto action
   can be used together with the snooze action.  The sections below
   describe these interactions.  Tagged arguments in future extensions
   to the fileinto action need to describe their interaction with the
   snooze extension, if any.




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   When any fileinto extension arguments are used with the snooze
   extension, the corresponding extension MUST be enabled, and the
   arguments are defined to have the same syntax, semantics, and
   treatment as they do with the fileinto action.

3.4.1.  Imap4flags Extension

   When the "imap4flags" [RFC5232] extension is enabled in a script, two
   additional tagged arguments are added to "snooze" that allow
   manipulating the set of flags on a snoozed message.

   AWAKEN-OPTIONS /= ADDFLAGS / REMOVEFLAGS

   ADDFLAGS    = ":addflags" string-list
   REMOVEFLAGS = ":removeflags" string-list

   The optional :addflags and :removeflags arguments are used to specify
   which IMAP [RFC3501] flags should be added to and/or removed from the
   set of IMAP flags present on the snoozed message at the time of
   awakening.  Note that depending on the method used to snooze a
   message, the set of IMAP flags present at the time of awakening may
   be the empty set.

   This document doesn't dictate how the Sieve interpreter will set the
   IMAP flags.  In particular, the Sieve interpreter may work as an IMAP
   client or may have direct access to the mailstore.

   The general requirements for flag handling specified in Section 2 of
   [RFC5232] MUST be followed.

3.4.2.  Mailbox Extension

   This document extends the definition of the ":create" [RFC5490]
   tagged argument so that it can be used with the snooze action.

   AWAKEN-OPTIONS /= CREATE

   CREATE = ":create"
              ; MUST NOT be appear unless MAILBOX also appears

   If the optional ":create" argument is specified with snooze, it
   instructs the Sieve interpreter to create the target mailbox, if
   needed, before attempting to file the awakened message into the
   target mailbox.







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3.4.3.  Special-Use Extension

   This document extends the definition of the ":specialuse" [RFC8579]
   tagged argument so that it can be used with the snooze action.

   AWAKEN-OPTIONS /= SPECIAL-USE

   SPECIAL-USE = ":specialuse" string

   If the optional ":specialuse" argument is specified with snooze, it
   instructs the Sieve interpreter to check whether a mailbox exists
   with the specific special-use flag assigned to it.  If such a mailbox
   exists, the awakened message is filed into the special-use mailbox.
   Otherwise, the awakened message is filed into the target mailbox.

   If both the optional ":specialuse" and ":create" arguments are
   specified with snooze, the Sieve interpreter is instructed to create
   the target mailbox per Section 4.1 of [RFC8579], if needed.

3.4.4.  MailboxID Extension

   This document extends the definition of the ":mailboxid"
   [I-D.gondwana-sieve-mailboxid] tagged argument so that it can be used
   with the snooze action.

   AWAKEN-OPTIONS /= MAILBOXID

   MAILBOXID = ":mailboxid" string

   If the optional ":mailboxid" argument is specified with snooze, it
   instructs the Sieve interpreter to check whether a mailbox exists in
   the user's personal namespace [RFC2342] with the specified MAILBOXID
   [RFC8474].  If such a mailbox exists, the awakened message is filed
   into that mailbox.  Otherwise, the awakened message is filed into the
   target mailbox.

   If both the optional ":mailboxid" and ":specialuse" arguments are
   specified with snooze, the Sieve interpreter is instructed to resolve
   the mailboxid first.  If a mailbox with the specified mailboxid does
   not exist, then the process in Section 3.4.3 is followed.

4.  Mechanics of Snoozing Messages

   The process of snoozing is implementation specific and outside the
   scope of this document.  However, the sections below outline possible
   methods of snoozing and awakening a message to be filed.





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4.1.  SMTP Future Message Release

   A Sieve interpreter may implement the snooze action by leveraging the
   SMTP Future Message Release [RFC4865] submission extension.  The
   message would be snoozed by queuing it for redelivery with a release
   time that corresponds to the calculated awaken time.  The target
   mailbox for the awakened message would need to be encoded into the
   recipient address or into a message header field.  Care MUST be taken
   to prevent the awakened message from being re-snoozed by the Sieve
   script and causing a message loop.

4.2.  "Snoozed" Mailbox

   A Sieve interpreter may implement the snooze action by leveraging the
   user's existing mail store.  The message would be snoozed by storing
   the message in a special "snoozed" mailbox and then moved into the
   target mailbox at the calculated awaken time.

   If a user's Sieve script enables the "imap4flags" [RFC5232]
   extension, and if the "setflag" and/or "addflag" actions have been
   used to store IMAP flags in the imap4flags internal variable, the
   Sieve interpreter MAY use the current value of the internal variable
   as the set of flags to associate with the message when storing it
   into the "snoozed" mailbox.  Note that in this case, the ":addflag"
   and ":removeflag" tagged arguments to the snooze action operate on
   this set of flags, but MUST NOT do so until the message is awakened.

5.  Implementation Status

   < RFC Editor: before publication please remove this section and the
   reference to [RFC7942] >

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC7942], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation



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   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

5.1.  Cyrus Server

   The open source Cyrus Server [1] project is a highly scalable
   enterprise mail system which supports Sieve email filtering at the
   point of final delivery.  This production level Sieve implementation
   supports all of the requirements described in this document.  This
   implementation is freely distributable under a BSD style license from
   Computing Services at Carnegie Mellon University [2].

6.  Security Considerations

   Security considerations are discussed in [RFC5228], [RFC5232],
   [RFC8579], and [I-D.gondwana-sieve-mailboxid].

   It is believed that this extension doesn't introduce any additional
   security concerns.

7.  Privacy Considerations

   It is believed that this extension doesn't introduce any privacy
   considerations beyond those in [RFC5228].

8.  IANA Considerations

8.1.  Registration of Sieve Extension

      To: iana@iana.org

      Subject: Registration of new Sieve extension

      Capability name: snooze

      Description: Adds the "snooze" action command to postpone filing a
      message into a target mailbox until a later point in time.

      RFC number: RFC XXXX

      Contact address: The Sieve discussion list <sieve@ietf.org>

9.  References







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9.1.  Normative References

   [I-D.gondwana-sieve-mailboxid]
              Gondwana, B., "Sieve Email Filtering: delivery by
              mailboxid", draft-gondwana-sieve-mailboxid-02 (work in
              progress), June 2020.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2342]  Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342,
              DOI 10.17487/RFC2342, May 1998,
              <https://www.rfc-editor.org/info/rfc2342>.

   [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
              <https://www.rfc-editor.org/info/rfc3501>.

   [RFC4234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 4234, DOI 10.17487/RFC4234,
              October 2005, <https://www.rfc-editor.org/info/rfc4234>.

   [RFC5228]  Guenther, P., Ed. and T. Showalter, Ed., "Sieve: An Email
              Filtering Language", RFC 5228, DOI 10.17487/RFC5228,
              January 2008, <https://www.rfc-editor.org/info/rfc5228>.

   [RFC5232]  Melnikov, A., "Sieve Email Filtering: Imap4flags
              Extension", RFC 5232, DOI 10.17487/RFC5232, January 2008,
              <https://www.rfc-editor.org/info/rfc5232>.

   [RFC5490]  Melnikov, A., "The Sieve Mail-Filtering Language --
              Extensions for Checking Mailbox Status and Accessing
              Mailbox Metadata", RFC 5490, DOI 10.17487/RFC5490, March
              2009, <https://www.rfc-editor.org/info/rfc5490>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8474]  Gondwana, B., Ed., "IMAP Extension for Object
              Identifiers", RFC 8474, DOI 10.17487/RFC8474, September
              2018, <https://www.rfc-editor.org/info/rfc8474>.

   [RFC8579]  Bosch, S., "Sieve Email Filtering: Delivering to Special-
              Use Mailboxes", RFC 8579, DOI 10.17487/RFC8579, May 2019,
              <https://www.rfc-editor.org/info/rfc8579>.



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   [tzdb]     Internet Assigned Numbers Authority, "Time Zone Database",
              <https://www.iana.org/time-zones>.

9.2.  Informative References

   [RFC4865]  White, G. and G. Vaudreuil, "SMTP Submission Service
              Extension for Future Message Release", RFC 4865,
              DOI 10.17487/RFC4865, May 2007,
              <https://www.rfc-editor.org/info/rfc4865>.

   [RFC5260]  Freed, N., "Sieve Email Filtering: Date and Index
              Extensions", RFC 5260, DOI 10.17487/RFC5260, July 2008,
              <https://www.rfc-editor.org/info/rfc5260>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

9.3.  URIs

   [1] http://www.cyrusimap.org/

   [2] http://www.cmu.edu/computing/

Authors' Addresses

   Kenneth Murchison
   Fastmail US LLC
   1429 Walnut Street - Suite 1201
   Philadelphia, PA  19102
   USA

   Email: murch@fastmailteam.com


   Ricardo Signes
   Fastmail US LLC
   1429 Walnut Street - Suite 1201
   Philadelphia, PA  19102
   USA

   Email: rjbs@fastmailteam.com








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   Neil Jenkins
   Fastmail Pty Ltd
   Level 2, 114 William Street
   Melbourne, VIC  3000
   Australia

   Email: neilj@fastmailteam.com












































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