]> Fastmail US LLC

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Fastmail US LLC

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Fastmail Pty Ltd

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

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 an extension to the Sieve language that enables scripts to postpone the delivery of a message into a target mailbox until a later point in time.

Conventions Used in This Document Conventions for notations are as in , 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 "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Capability Identifier Sieve implementations that support this extension have an identifier of "snooze" for use with the capability mechanism.

Snooze Action ]]> The AWAKEN-OPTIONS argument is defined here in ABNF syntax so that it can be modified by other extensions. The "snooze" action cancels the implicit keep and postpones delivery of the message into the specified mailbox at a later point in time. The snooze action is semantically equivalent to a delayed fileinto action (see ). The arguments of the snooze action specify when, where, and how the awakened message will be filed. The process of actually snoozing the message is implementation specific and outside the scope of this document. However, implementations MUST ensure that the intended recipient has access to the message while snoozed. To that end, a Sieve interpreter MAY implement the snooze action by delivering the message to a special "snoozed" mailbox within its mailstore. IMAP and JMAP servers MUST apply the "Snoozed" attribute to this mailbox. The message will reside in this special mailbox until the prescribed awaken time at which it will be moved into the specified target mailbox.

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 ). 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 an 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.

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

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. 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.

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.

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.

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.

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

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. 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.

Imap4flags Extension When the "imap4flags" 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. The optional :addflags and :removeflags arguments are used to specify which IMAP 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 the set of IMAP flags present at the time of awakening may be the empty set. If the "setflag" and/or "addflag" actions have been used to store IMAP flags in the imap4flags internal variable, the Sieve interpreter MUST 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. 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 MUST be followed.

Example The following example leverages the Date, Relational, and Imap4flags extensions to snooze messages received after business hours until the following work day. Note that the message is marked as important when it is snoozed, and will be marked as unread when it is awakened.

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

Special-Use Extension This document extends the definition of the ":specialuse" tagged argument so that it can be used with the snooze action. 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 , if needed.

MailboxID Extension This document extends the definition of the ":mailboxid" tagged argument so that it can be used with the snooze action. 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 with the specified MAILBOXID. If such a mailbox exists, the awakened message is filed into that mailbox. Otherwise, the awakened message is filed into the target mailbox. It is an error to specify both ":mailboxid" and ":specialuse" in the same snooze action.

Implementation Status < RFC Editor: before publication please remove this section and the reference to > 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 . 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 , "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 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".

Cyrus Server The open source Cyrus Server 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.

Security Considerations Security considerations are discussed in , , , and . It is believed that this extension doesn't introduce any additional security concerns.

Privacy Considerations It is believed that this extension doesn't introduce any privacy considerations beyond those in .

IANA Considerations

Registration of Sieve Extension This document defines the following new Sieve extension to be added to the registry defined in and located here: IANA are requested to add a capability to the Sieve Extensions registry:

• To: iana@iana.org
• Subject: Registration of new Sieve extension
• Capability name: snooze
• Description: Adds the "snooze" action command to postpone delivery of 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>

Registration of Sieve Action This document defines the following new Sieve action to be added to the registry defined in . IANA are requested to add an action to the Sieve Action registry:

• Name: snooze
• Description: Postpone delivery of a message into a target mailbox until a later point in time.
• References: RFC XXXX, , , ,
• Capabilities: "snooze", "imap4flags", "mailbox", "special-use", "mailboxid".
• Interactions: Is not compatible with the reject or ereject actions.
• Cancels Implicit Keep?: Y
• Use with IMAP Events?: Y
• Comments: Requires a special "snoozed" mailbox in the mailstore.

Registration of IMAP Mailbox Name Attribute This document defines the following new IMAP mailbox name attribute to be added to the registry defined in and located here: IANA are requested to add an attribute to the IMAP Mailbox Name Attribute registry:

• To: iana@iana.org
• Subject: Registration of new IMAP Mailbox Name Attribute
• Attribute name: Snoozed
• Description: Messages that have been snoozed.
• Reference: RFC XXXX

Acknowledgments The authors would like to thank the following individuals for contributing their ideas and support for writing this specification: Ned Freed, Barry Leiba, and Alexey Melnikov.

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document defines a NAMESPACE command that allows a client to discover the prefixes of namespaces used by a server for personal mailboxes, other users' mailboxes, and shared mailboxes. [STANDARDS-TRACK] The Internet Message Access Protocol, Version 4rev1 (IMAP4rev1) allows a client to access and manipulate electronic mail messages on a server. IMAP4rev1 permits manipulation of mailboxes (remote message folders) in a way that is functionally equivalent to local folders. IMAP4rev1 also provides the capability for an offline client to resynchronize with the server. IMAP4rev1 includes operations for creating, deleting, and renaming mailboxes, checking for new messages, permanently removing messages, setting and clearing flags, RFC 2822 and RFC 2045 parsing, searching, and selective fetching of message attributes, texts, and portions thereof. Messages in IMAP4rev1 are accessed by the use of numbers. These numbers are either message sequence numbers or unique identifiers. IMAP4rev1 supports a single server. A mechanism for accessing configuration information to support multiple IMAP4rev1 servers is discussed in RFC 2244. IMAP4rev1 does not specify a means of posting mail; this function is handled by a mail transfer protocol such as RFC 2821. [STANDARDS-TRACK] Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity, with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK] This document describes a language for filtering email messages at time of final delivery. It is designed to be implementable on either a mail client or mail server. It is meant to be extensible, simple, and independent of access protocol, mail architecture, and operating system. It is suitable for running on a mail server where users may not be allowed to execute arbitrary programs, such as on black box Internet Message Access Protocol (IMAP) servers, as the base language has no variables, loops, or ability to shell out to external programs. [STANDARDS-TRACK] Recent discussions have shown that it is desirable to set different IMAP (RFC 3501) flags on message delivery. This can be done, for example, by a Sieve interpreter that works as a part of a Mail Delivery Agent. This document describes an extension to the Sieve mail filtering language for setting IMAP flags. The extension allows setting of both IMAP system flags and IMAP keywords. [STANDARDS-TRACK] This memo defines an extension to the Sieve mail filtering language (RFC 5228) for accessing mailbox and server annotations, checking for mailbox existence, and controlling mailbox creation on "fileinto" action. [STANDARDS-TRACK] RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document updates RFC 3501 (IMAP4rev1) with persistent identifiers on mailboxes and messages to allow clients to more efficiently reuse cached data when resources have changed location on the server. 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. RFC 6154 created an IMAP special-use LIST extension and defined an initial set of attributes. This document defines a new attribute, "\Important", and establishes a new IANA registry for IMAP folder attributes, which include the attributes defined in RFCs 5258, 3501, and 6154. This document also defines a new IMAP keyword, "$Important", and registers it in the registry defined in RFC 5788. The OBJECTID capability of IMAP (RFC 8474) allows clients to identify mailboxes by a unique identifier that survives renaming. This document extends the Sieve email filtering language (RFC 5228) to allow using that same unique identifier as a target for fileinto rules and for testing the existence of mailboxes. Isode Ltd Fastmail US LLC Sieve Email Filtering Language (RFC 5228) is a popular email filtering language used upon final mail delivery. This document creates a registry of Sieve (RFC 5228) actions in order to help developers and Sieve extension writers track interactions between different extensions. Internet Assigned Numbers Authority Informative References This document describes the "date" and "index" extensions to the Sieve email filtering language. The "date" extension gives Sieve the ability to test date and time values in various ways. The "index" extension provides a means to limit header and address tests to specific instances of header fields when header fields are repeated. [STANDARDS-TRACK] This document describes the RELATIONAL extension to the Sieve mail filtering language defined in RFC 3028. This extension extends existing conditional tests in Sieve to allow relational operators. In addition to testing their content, it also allows for testing of the number of entities in header and envelope fields. This document obsoletes RFC 3431. [STANDARDS-TRACK] This document describes a simple process that allows authors of Internet-Drafts to record the status of known implementations by including an Implementation Status section. 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 and feedback that have made the implemented protocols more mature. This process is not mandatory. Authors of Internet-Drafts are encouraged to consider using the process for their documents, and working groups are invited to think about applying the process to all of their protocol specifications. This document obsoletes RFC 6982, advancing it to a Best Current Practice. This document specifies a data model for synchronising email data with a server using the JSON Meta Application Protocol (JMAP). Clients can use this to efficiently search, access, organise, and send messages, and to get push notifications for fast resynchronisation when new messages are delivered or a change is made in another client.

Change History (To be removed by RFC Editor before publication) Changes since draft-ietf-extra-sieve-snooze-05:

• Don't require implementations to use a "snoozed" mailbox.

Changes since draft-ietf-extra-sieve-snooze-04:

• Miscellaneous editorial changes.

Changes since draft-ietf-extra-sieve-snooze-03:

• Added "snooze" to the Sieve Actions Registry.

Changes since draft-ietf-extra-sieve-snooze-02:

• Updated :mailboxid reference to RFC9042.
• Added an informative reference to RFC8621.
• Miscellaneous editorial changes.

Changes since draft-ietf-extra-sieve-snooze-01:

• Miscellaneous editorial changes.

Changes since draft-ietf-extra-sieve-snooze-00:

• Disallow both :mailboxid and :specialuse in the same snooze action.
• Updated :mailboxid reference to draft-ietf-extra-sieve-mailboxid
• Specified that snooze cancels implicit keep.
• Specified that implementations MUST use a "snoozed" mailbox.
• Added registration of \Snoozed Special-Use Attribute.
• Added example of manipulating IMAP flags at both snooze time and awaken time.
• Miscellaneous editorial changes.