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