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rfc:rfc6785

Internet Engineering Task Force (IETF) B. Leiba Request for Comments: 6785 Huawei Technologies Updates: 5228 November 2012 Category: Standards Track ISSN: 2070-1721

Support for Internet Message Access Protocol (IMAP) Events in Sieve

Abstract

 Sieve defines an email filtering language that can, in principle,
 plug into any point in the processing of an email message.  As
 defined in the base specification, it plugs into mail delivery.  This
 document defines how Sieve can plug into points in IMAP where
 messages are created or changed, adding the option of user-defined or
 installation-defined filtering (or, with Sieve extensions, features
 such as notifications).  Because this requires future Sieve
 extensions to specify their interactions with this one, this document
 updates the base Sieve specification, RFC 5228.

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 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6785.

Leiba Standards Track [Page 1] RFC 6785 IMAP Events in Sieve November 2012

Copyright Notice

 Copyright (c) 2012 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
 (http://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.

Table of Contents

 1. Introduction ....................................................3
    1.1. Overview ...................................................3
    1.2. Differences between IMAP Events and Mail Delivery ..........4
    1.3. Conventions Used in This Document ..........................5
 2. The "IMAP Events in Sieve" Extension ............................5
    2.1. The "imapsieve" Capability Strings .........................5
    2.2. Existing IMAP Functions Affected by IMAP Events in Sieve ...5
         2.2.1. The IMAP APPEND Command .............................6
         2.2.2. The IMAP COPY Command ...............................6
         2.2.3. Changes to IMAP Message Flags .......................6
         2.2.4. When Script Actions Set the \Deleted Flag ...........7
    2.3. New Functions Defined by IMAP Events in Sieve ..............7
         2.3.1. Interaction with Metadata ...........................7
 3. Applicable Sieve Actions and Interactions .......................8
    3.1. The Implicit Keep ..........................................9
    3.2. The "keep" Action ..........................................9
    3.3. The "fileinto" Action ......................................9
    3.4. The "redirect" Action ......................................9
    3.5. The "discard" Action ......................................10
    3.6. The "notify" Action .......................................10
    3.7. The "addheader" and "deleteheader" Actions ................10
    3.8. The "setflag", "deleteflag", and "removeflag" Actions .....11
    3.9. MIME Part Tests and Replacement ...........................11
    3.10. spamtest and virustest ...................................11
    3.11. Inapplicable Actions .....................................11
    3.12. Future Sieve Actions .....................................12

Leiba Standards Track [Page 2] RFC 6785 IMAP Events in Sieve November 2012

 4. Interaction with Sieve Environment .............................12
    4.1. Base Sieve Environment Items: location and phase ..........12
    4.2. New Sieve Environment Items: imap.user and imap.email .....12
    4.3. New Sieve Environment Item: imap.cause ....................13
    4.4. New Sieve Environment Item: imap.mailbox ..................13
    4.5. New Sieve Environment Item: imap.changedflags .............13
    4.6. Interaction with Sieve Tests (Comparisons) ................13
 5. Examples .......................................................14
 6. Security Considerations ........................................15
 7. IANA Considerations ............................................16
    7.1. Registration of "imapsieve" IMAP Capability ...............16
    7.2. Registration of "imapsieve" Sieve Extension ...............16
    7.3. Registration of Sieve Environment Items ...................16
         7.3.1. Registration of Sieve Environment Item:
                imap.cause .........................................16
         7.3.2. Registration of Sieve Environment Item:
                imap.mailbox .......................................17
         7.3.3. Registration of Sieve Environment Item:
                imap.changedflags ..................................17
         7.3.4. Registration of Sieve Environment Item: imap.user ..17
         7.3.5. Registration of Sieve Environment Item:
                imap.email .........................................17
    7.4. Registration of IMAP METADATA Mailbox Entry Name ..........18
    7.5. Registration of IMAP METADATA Server Entry Name ...........18
 8. References .....................................................18
    8.1. Normative References ......................................18
    8.2. Informative References ....................................19

1. Introduction

1.1. Overview

 Some applications have a need to apply Sieve filters [RFC5228] in
 contexts other than initial mail delivery.  This is especially true
 in diverse service environments, such as when the client is
 sporadically connected, is connected through a high-latency or
 high-cost channel, or is on a limited-function device.  For such
 clients, it may be very important, for higher performance and
 reliability, to take advantage of server capabilities, including
 those provided by Sieve filtering (and Sieve extensions, such as
 Notify [RFC5435]).

Leiba Standards Track [Page 3] RFC 6785 IMAP Events in Sieve November 2012

 This specification defines extensions to IMAP [RFC3501] to support
 the invocation of Sieve scripts at times when the IMAP server creates
 new messages or modifies existing ones.  It also defines how Sieve
 scripts will process these invocations.  Support for IMAP events in
 Sieve also requires support for the following:
 o  IMAP Metadata [RFC5464], because Metadata is used to associate
    scripts with IMAP mailboxes.
 o  Sieve Environment [RFC5183], because it defines an important way
    for Sieve scripts to test the conditions under which they have
    been invoked.
 o  Sieve imap4flags [RFC5232], because it provides important
    functionality in handling IMAP events related to flag changes.
 Because this requires future Sieve extensions to specify their
 interactions with this one (see Section 3.12), this document updates
 the base Sieve specification, RFC 5228.

1.2. Differences between IMAP Events and Mail Delivery

 Invoking Sieve scripts in a context other than initial mail delivery
 introduces new situations; this changes the applicability of Sieve
 features, creates implementation challenges, and creates user
 interface issues.  This section discusses some of those differences,
 challenges, and issues.
 At times other than message delivery, delivery "envelope" information
 might not be available.  With messages added through IMAP APPEND,
 there might be no way to even guess who the intended recipient is,
 and no concept of who "sent" the message.  Sieve actions that relate
 to contacting the sender, for example, will not be applicable.
 Because IMAP events will often be triggered by user actions, and
 because user interfaces allow bulk actions that differ from
 individual message arrival, it now becomes possible for a single user
 action, such as drag-and-drop, to initiate Sieve script processing on
 a large number of messages at once.  Implementations will have to
 deal with such situations as a "COPY" action or flag changes on
 dozens, or even thousands, of messages.
 Other issues might surface as this extension is deployed and
 experience with it develops.

Leiba Standards Track [Page 4] RFC 6785 IMAP Events in Sieve November 2012

1.3. Conventions Used in This Document

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].

2. The "IMAP Events in Sieve" Extension

2.1. The "imapsieve" Capability Strings

 An IMAP server advertises support for IMAP events in Sieve through
 the "imapsieve" capability.  A server that advertises "imapsieve" is
 claiming to be in compliance with this specification in all aspects.
 The syntax of the "imapsieve" capability string is defined as
 follows:
 capability /=  "IMAPSIEVE=" sieveurl-server
         ; <sieveurl-server> is defined in RFC 5804, Section 3
 Only one "imapsieve" capability string, specifying one
 sieveurl-server, is allowed to be present.  The sieveurl-server
 identifies the ManageSieve server that clients need to contact for
 managing Sieve scripts associated with this IMAP server.
 The corresponding Sieve implementation uses the Sieve capability
 string "imapsieve", and Sieve scripts that depend upon the IMAP
 events MUST include that string in their "required" lists.
 Implementations that support IMAP events in Sieve MUST also support
 IMAP Metadata [RFC5464] and Sieve Environment [RFC5183], because
 Metadata is used to associate scripts with IMAP mailboxes and
 Environment defines an important way for Sieve scripts to test the
 conditions under which they have been invoked.  Notwithstanding the
 support requirement, scripts that directly use Environment MUST also
 include its capability string in their "required" lists.

2.2. Existing IMAP Functions Affected by IMAP Events in Sieve

 The subsections below describe in detail the IMAP commands and
 situations on which IMAP events in Sieve have an effect.  Not all
 Sieve actions make sense in the case of messages affected by IMAP
 commands.  See Section 3 for details.
 It's important to note that since the base Sieve specification (see
 [RFC5228]) and its extensions define functions for scripts that are
 invoked during initial mail delivery, those function definitions are
 necessarily tailored to and limited by that context.  This document
 extends those function definitions for use during IMAP events.  By

Leiba Standards Track [Page 5] RFC 6785 IMAP Events in Sieve November 2012

 nature of that, Sieve functions, in this extended context, may behave
 somewhat differently, though their extended behavior will still be
 consistent with the functions' goals.
 If more than one message is affected at the same time, each message
 triggers the execution of a Sieve script separately.  The scripts MAY
 be run in parallel.

2.2.1. The IMAP APPEND Command

 A message may be added to a mailbox through the IMAP APPEND command.
 In a server that advertises "imapsieve", new messages added in this
 way MUST trigger the execution of a Sieve script, subject to the
 settings defined through Metadata (see Section 2.3.1).
 If the IMAP server also supports the IMAP MULTIAPPEND extension
 [RFC3502], the APPEND command can create more than one message at a
 time.  In that case, each message creation is considered a separate
 event, and any applicable Sieve script is called once for each
 message.

2.2.2. The IMAP COPY Command

 One or more messages may be added to a mailbox through the IMAP COPY
 command.  In a server that advertises "imapsieve", new messages added
 in this way MUST trigger the execution of a Sieve script, subject to
 the settings defined through Metadata.

2.2.3. Changes to IMAP Message Flags

 One or more existing messages can have their flags changed in a
 number of ways, including:
 o  The FETCH command (may cause the \Seen flag to be set).
 o  The STORE command (may cause the \Answered, \Deleted, \Draft,
    \Flagged, and \Seen flags to be set or reset, and may cause
    keywords to be set or reset).
 o  The invocation of a Sieve script on an existing message, where the
    script uses one of the actions defined in the imap4flags extension
    [RFC5232] to change the flags.
 In a server that advertises "imapsieve", messages whose flags are
 changed in any way (except as explained in the next sentence) MUST
 trigger the execution of a Sieve script, subject to the settings
 defined through Metadata.  The exception is that in order to avoid
 script loops, flag changes that are made as a result of a script that

Leiba Standards Track [Page 6] RFC 6785 IMAP Events in Sieve November 2012

 was itself invoked because of flag changes SHOULD NOT result in a
 further invocation of the script.  In any case, implementations MUST
 take steps to avoid such loops.
 For flag-change events, the Sieve script will see the message flags
 as they are AFTER the changes.

2.2.4. When Script Actions Set the \Deleted Flag

 There are times when the actions "fileinto" (see Section 3.3),
 "redirect" (see Section 3.4), and "discard" (see Section 3.5) will
 set the \Deleted flag on the message.  In those cases, the following
 apply:
 When the \Deleted flag is set by the script, a flag-change Sieve
 script is not invoked.
 The implementation MAY then expunge the original message (WITHOUT
 expunging other messages in the mailbox).  Alternatively, it might
 have expunges batched or done by a user.  (It might be helpful to
 allow the user to make this choice through a preference.)
 If the server does the expunge, the effect is as though a client had
 flagged the message and done a UID EXPUNGE (see [RFC4315]) on the
 affected message(s) only.  Handling it this way allows clients to
 handle messages consistently and avoids hidden changes that might
 invalidate their message caches.

2.3. New Functions Defined by IMAP Events in Sieve

2.3.1. Interaction with Metadata

 Support for IMAP events in Sieve requires support for IMAP Metadata
 [RFC5464] as well, since the latter is used to associate scripts with
 IMAP mailboxes.
 When an applicable event occurs on an IMAP mailbox, if there is an
 IMAP metadata entry named "/shared/imapsieve/script" for the mailbox,
 that entry is used.  If there is not, but there is an IMAP metadata
 entry named "/shared/imapsieve/script" for the server, that entry is
 used (providing a way to define a global script for all mailboxes on
 a server).  If neither entry exists, then no script will be invoked.
 If a "/shared/imapsieve/script" metadata entry was selected above,
 its value is used as the name of the Sieve script that will be
 invoked in response to the IMAP event.  If the value is empty, then
 no script is run.  The selection of which metadata entry to use

Leiba Standards Track [Page 7] RFC 6785 IMAP Events in Sieve November 2012

 happens before any examination of the contents of the entry.  If the
 mailbox entry is selected and is then found to be unusable or empty,
 the server entry is not used as a backup: no script is run.
 This specifies the mechanism for "activating" a script for a given
 mailbox (or for all mailboxes) but does not specify a mechanism for
 creating, storing, or validating the script.  Implementations MUST
 support ManageSieve [RFC5804] and can use the PUTSCRIPT command to
 store the script without using the SETACTIVE command to activate it.
 Script names used in "/shared/imapsieve/script" metadata entries are
 the script names used on the corresponding ManageSieve server.  If a
 "/shared/imapsieve/script" metadata entry contains a script name that
 doesn't exist in the ManageSieve server, then no Sieve script will be
 invoked for IMAP Sieve events.
 Only one Sieve script may currently be defined per mailbox,
 eliminating the complexity and possible ambiguity involved with
 coordinating the results of multiple scripts.  Any sub-filtering is
 done in the Sieve script.  For example, if it's only necessary to
 deal with flag changes, but not with new messages appended or copied,
 the Sieve script will still be invoked for all events, and the script
 is responsible for checking the event type.
 The possibility is open for an extension to add support for multiple
 scripts -- for example, per-client scripts on a multi-client user's
 inbox, or per-user scripts on a mailbox that is shared among users.
 Because this metadata name is associated with the mailbox, there can
 (and it's expected that there will) be different scripts associated
 with events for different mailboxes.  Indeed, most mailboxes will
 probably invoke no script at all.

3. Applicable Sieve Actions and Interactions

 Since some Sieve actions relate specifically to the delivery of mail,
 not all actions and extensions make sense when the messages are
 created by other means or when changes are made to data associated
 with existing messages.  This section describes how actions in the
 base Sieve specification, and those in extensions known at the time
 of this writing, relate to this specification.
 In addition to what is specified here, interactions noted in the
 individual specifications apply and must be considered.

Leiba Standards Track [Page 8] RFC 6785 IMAP Events in Sieve November 2012

3.1. The Implicit Keep

 For all cases that fall under IMAP events in Sieve, the implicit keep
 means that the message is treated as it would have been if no Sieve
 script were run.  For APPEND and COPY, the message is stored into the
 target mailbox normally.  For flag changes, the message is left in
 the mailbox.  If actions have been taken that change the message,
 those changes are considered transient and MUST NOT be retained for
 any "keep" action (because IMAP messages are immutable).  No error is
 generated, but the original message, without the changes, is kept.

3.2. The "keep" Action

 The "keep" action is applicable in all cases that fall under IMAP
 events in Sieve.  Its behavior is as described for implicit keep, in
 Section 3.1.

3.3. The "fileinto" Action

 If the Sieve implementation supports the "fileinto" action, that
 action is applicable in all cases that fall under IMAP events in
 Sieve.  If the "copy" extension [RFC3894] is available and the :copy
 option is specified, the implicit keep is retained; otherwise,
 fileinto cancels the implicit keep, as specified in the base Sieve
 specification.
 For APPEND and COPY, the message is stored into the fileinto mailbox
 IN ADDITION TO the original target mailbox.  For flag changes, the
 message is COPIED into the fileinto mailbox, without removing the
 original.  In all cases, fileinto always creates a new message,
 separate from the original.
 The "fileinto" action is not an IMAP APPEND or COPY and therefore
 does not result in a subsequent event (see also the Security
 Considerations, Section 6).
 If a "keep" action is not also in effect, the original message is
 then marked with the \Deleted flag (see Section 2.2.4).

3.4. The "redirect" Action

 The "redirect" action is applicable in all cases that fall under IMAP
 events in Sieve.  It causes the message to be sent, as specified in
 the base Sieve specification, to the designated address.  If the
 "copy" extension [RFC3894] is available and the :copy option is
 specified, the implicit keep is retained; otherwise, redirect cancels
 the implicit keep, as specified in the base Sieve specification.

Leiba Standards Track [Page 9] RFC 6785 IMAP Events in Sieve November 2012

 It's possible that a message processed in this way does not have the
 information necessary to be redirected properly.  It might lack
 necessary header information, and there might not be appropriate
 information for the MAIL FROM command.  In such cases, the "redirect"
 action uses message submission [RFC6409], and it is up to the Sieve
 engine to supply the missing information.  The redirect address is,
 of course, used for the "RCPT TO", and the "MAIL FROM" SHOULD be set
 to the address of the owner of the mailbox.  The message submission
 server is allowed, according to the message submission protocol, to
 perform necessary fix-up to the message (see Section 8 of RFC 6409).
 It can also reject the submission attempt if the message is too
 ill-formed for submission.
 For APPEND and COPY, the message is stored into the target mailbox in
 addition to being redirected.  For flag changes, the message remains
 in its original mailbox.
 If a "keep" action is not also in effect, the original message is
 then marked with the \Deleted flag (see Section 2.2.4).

3.5. The "discard" Action

 The "discard" action is applicable in all cases that fall under IMAP
 events in Sieve.  For APPEND and COPY, the message is first stored
 into the target mailbox.  If an explicit "keep" action is also in
 effect, the "discard" action now does nothing.  Otherwise, the
 original message is then marked with the \Deleted flag (see
 Section 2.2.4).

3.6. The "notify" Action

 If the Sieve notify extension [RFC5435] is available, the "notify"
 action is applicable in all cases that fall under IMAP events in
 Sieve.  The result is that the requested notification is sent and
 that the message is otherwise handled as it would normally have been.

3.7. The "addheader" and "deleteheader" Actions

 If the editheader extension [RFC5293] is available, it can be used to
 make transient changes to header fields, which aren't saved in place,
 such as for "redirect" or "fileinto" actions.  Because messages in
 IMAP mailboxes are immutable, such changes are not applicable for the
 "keep" action (explicit or implicit).  See Section 3.1.

Leiba Standards Track [Page 10] RFC 6785 IMAP Events in Sieve November 2012

3.8. The "setflag", "deleteflag", and "removeflag" Actions

 Implementations of IMAP events in Sieve MUST also support the
 imap4flags extension [RFC5232], and the actions associated with it
 are all applicable to any case that falls under IMAP events in Sieve.
 It is worth noting also that the "hasflag" test that is defined in
 the imap4flags extension might be particularly useful in scripts
 triggered by flag changes ("hasflag" will see the new, changed
 flags).  The flag changes behave as though a client had made the
 change.
 As explained above, in order to avoid script loops, flag changes that
 are made as a result of a script that was itself invoked because of
 flag changes SHOULD NOT result in another script invocation.  In any
 case, implementations MUST take steps to avoid such loops.

3.9. MIME Part Tests and Replacement

 If the MIME Part Tests extension [RFC5703] is available, all of its
 functions can be used, but any changes made to the message, using the
 "replace" or "enclose" action, MUST be considered transient and are
 only applicable with actions such as "redirect" and "fileinto".
 Because messages in IMAP mailboxes are immutable, such changes are
 not applicable for the "keep" action (explicit or implicit).  See
 Section 3.1.

3.10. spamtest and virustest

 If the spamtest and virustest extensions [RFC5235] are available,
 they are applicable in all cases that fall under IMAP events in
 Sieve.

3.11. Inapplicable Actions

 The following actions and extensions are not applicable to any case
 that falls under IMAP events in Sieve, because they are specifically
 designed to respond to delivery of a new email message.  Their
 appearance in the "require" control or their use in an IMAP event
 MUST result in an error condition that will terminate the Sieve
 script:
    reject [RFC5228]
    ereject [RFC5429]
    vacation [RFC5230]

Leiba Standards Track [Page 11] RFC 6785 IMAP Events in Sieve November 2012

 Future extensions that are specifically designed to respond to
 delivery of a new email message will likewise not be applicable to
 this extension.

3.12. Future Sieve Actions

 As noted above, future extensions that are specifically designed to
 respond to delivery of a new email message will not be applicable to
 this extension, because this extension does not involve acting at
 new-message delivery time.
 In general, future extensions to Sieve that define new actions MUST
 specify the applicability of those actions to this specification.

4. Interaction with Sieve Environment

4.1. Base Sieve Environment Items: location and phase

 The Sieve Environment extension defines a set of standard environment
 items (see [RFC5183], Section 4.1).  Two of those items are affected
 when the script is invoked through an IMAP event.
 The value of "location" is set to "MS" -- evaluation is being
 performed by a Message Store.
 The value of "phase" is set to "post" -- processing is taking place
 after (or perhaps instead of, in the case of APPEND) final delivery.

4.2. New Sieve Environment Items: imap.user and imap.email

 In the normal case, when Sieve is used in final delivery, there is no
 identity for the "filer" -- the user who is creating or changing the
 message.  In this case, there is such an identity, and a Sieve script
 might want to access that identity.
 Implementations MUST set and make available two new environment
 items:
 "imap.user" -- the identity (login ID) of the IMAP user that caused
 the action.  This MUST be the empty string if it is accessed during
 normal (final delivery) Sieve processing.
 "imap.email" -- the primary email address of the IMAP user that
 caused the action (the user identified by "imap.user").  In some
 implementations, "imap.user" and "imap.email" might have the same
 value.  This MUST be the empty string if it is accessed during normal
 (final delivery) Sieve processing.

Leiba Standards Track [Page 12] RFC 6785 IMAP Events in Sieve November 2012

4.3. New Sieve Environment Item: imap.cause

 Each mailbox uses a single script for all the change conditions
 described in this document (append, copy, flag changes).  To support
 that, the implementation MUST set the Environment [RFC5183] item
 "imap.cause", which contains the name of the action that caused the
 script to be invoked.  Its value is one of the following:
 o  APPEND (for invocations resulting from APPEND commands)
 o  COPY (for invocations resulting from COPY commands)
 o  FLAG (for invocations resulting from flag changes)
 Future extensions might define new events and, thus, new causes.
 Such extensions will come with their own capability strings, and the
 events they define will only be presented when their capabilities are
 requested.  Scripts that do not request those capabilities will not
 see those events and will not encounter the new cause strings.

4.4. New Sieve Environment Item: imap.mailbox

 The implementation MUST set the Environment [RFC5183] item
 "imap.mailbox" to the name of the mailbox that the affected message
 is in, in the case of existing messages, or is targeted to be stored
 into, in the case of new messages.  The value of this item is fixed
 when the script begins, and, in particular, MUST NOT change as a
 result of any action, such as "fileinto".

4.5. New Sieve Environment Item: imap.changedflags

 If the script was invoked because of flag changes to an existing
 message, the implementation MUST set the Environment [RFC5183] item
 "imap.changedflags" to the name(s) of the flag(s) that have changed.
 If the script was not invoked because of flag changes, the value of
 this item MUST be the empty string.  The script will not know from
 this item whether the flags have been set or reset, but it can use
 the "hasflag" test to determine the current value.  See example 2 in
 Section 5 for an example of how this might be used.

4.6. Interaction with Sieve Tests (Comparisons)

 Any tests against message envelope information, including the
 "envelope" test in the Sieve base specification, as well as any such
 test defined in extensions, are either inapplicable or have serious
 interoperability issues when performed at other than final-delivery
 time.  Therefore, envelope tests MUST NOT be permitted in the cases
 described here, and their use MUST generate a runtime error.

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 This extension does not affect the operation of other tests or
 comparisons in the Sieve base specification.

5. Examples

 Example 1:
 If a new message is added to the "ActionItems" mailbox, a copy is
 sent to the address "actionitems@example.com".
   require ["copy", "environment", "imapsieve"];
   if anyof (environment :is "imap.cause" "APPEND",
             environment :is "imap.cause" "COPY")  {
       if environment :is "imap.mailbox" "ActionItems" {
           redirect :copy "actionitems@example.com";
       }
   }
 Example 2:
 If the script is called for any message with the \Flagged flag set
 (tested through the imap4flags extension [RFC5232]) AND this script
 invocation represents a change to that flag, then a notification is
 sent using the Sieve notify extension [RFC5435].  No notification
 will be sent, though, if we're called with an existing message that
 already had that flag set.
   require ["enotify", "imap4flags", "variables",
            "environment", "imapsieve"];
   if environment :matches "imap.mailbox" "*" {
       set "mailbox" "${1}";
   }
   if allof (hasflag "\\Flagged",
             environment :contains "imap.changedflags" "\\Flagged") {
     notify :message "Important message in ${mailbox}"
         "xmpp:tim@example.com?message;subject=SIEVE";
   }

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 Example 3:
 This shows an example IMAP CAPABILITY response when this extension is
 supported.  The client has done STARTTLS with the server and is now
 inspecting capabilities.  (The untagged CAPABILITY response is split
 here for readability only, but it will be in one response message.)
   C:  A01 CAPABILITY
   S:  * CAPABILITY IMAP4rev1 AUTH=PLAIN UIDPLUS LIST-EXTENDED
         ACL IMAPSIEVE=sieve://sieve.example.com MULTISEARCH
   S:  A01 OK done

6. Security Considerations

 It is possible to introduce script processing loops by having a Sieve
 script that is triggered by flag changes use the actions defined in
 the imap4flags extension [RFC5232].  Implementations MUST take steps
 to prevent script loops.  One way to avoid this problem is that if a
 script is invoked by flag changes, and that script further changes
 the flags, those flag changes SHOULD NOT trigger a Sieve script
 invocation.
 The "fileinto" action never results in the invocation of a script.
 If an implementation did invoke a script as the result of a fileinto,
 as though an IMAP APPEND or COPY had been done, script loops could
 result (mailbox A responds to all COPY events by doing "fileinto B",
 and mailbox B responds to all COPY events by doing "fileinto A").  In
 general, actions taken as a result of the Sieve script are not IMAP
 events and do not themselves trigger Sieve script invocations.
 It is also possible to introduce loops through the "redirect" or
 "notify" actions.  See Sieve [RFC5228], Section 10, Sieve Notify
 [RFC5435], Section 8, and the Security Considerations sections of the
 applicable notification-method documents for loop-prevention
 information.  This extension does not change any of that advice.
 This extension introduces side effects to IMAP commands that users
 and script authors might not be aware of and that can accidentally be
 triggered by an operation that the user would expect to be innocuous.
 In particular, certain actions, such as "redirect", can cause a
 message (such as a message appended to a mailbox by a user) to be
 sent to the Internet in response to something as simple as a flag
 change.  For example, a script might cause messages marked for
 deletion to be sent to some off-site archiving service.  If a user
 appends a draft message to a mailbox (perhaps an unencrypted draft
 message) and then marks it for deletion, it might be very surprising
 to the user that the message is sent off site.  Script authors need
 to be careful not to create these kinds of surprises, especially when
 creating global scripts.

Leiba Standards Track [Page 15] RFC 6785 IMAP Events in Sieve November 2012

 Other security considerations are discussed in IMAP [RFC3501] and
 Sieve [RFC5228], as well as in some of the other extension documents.

7. IANA Considerations

7.1. Registration of "imapsieve" IMAP Capability

 IANA has added "IMAPSIEVE=" to the IMAP 4 Capabilities registry
 (<http://www.iana.org/assignments/imap4-capabilities>), according to
 the IMAP 4 specification [RFC3501].

7.2. Registration of "imapsieve" Sieve Extension

 The following information has been added to the Sieve Extensions
 registry (<http://www.iana.org/assignments/sieve-extensions>),
 according to the Sieve specification [RFC5228].
 Capability name: imapsieve
 Description: Add Sieve processing for IMAP events.
 RFC number: 6785
 Contact address: Sieve mailing list <sieve@ietf.org>

7.3. Registration of Sieve Environment Items

 The following subsections register items in the Sieve Environment
 Items registry
 (<http://www.iana.org/assignments/sieve-environment-items>),
 according to the Environment extension [RFC5183].

7.3.1. Registration of Sieve Environment Item: imap.cause

 Item name: imap.cause
 Description: The name of the action that caused the script to be
    invoked.  Its value is one of the following:
 o  APPEND (for invocations resulting from APPEND commands)
 o  COPY (for invocations resulting from COPY commands)
 o  FLAG (for invocations resulting from flag changes)
 RFC number: 6785
 Contact address: Sieve mailing list <sieve@ietf.org>

Leiba Standards Track [Page 16] RFC 6785 IMAP Events in Sieve November 2012

7.3.2. Registration of Sieve Environment Item: imap.mailbox

 Item name: imap.mailbox
 Description: The name of the mailbox that the affected message is in,
    in the case of existing messages, or is targeted to be stored
    into, in the case of new messages.  The value of this item is
    fixed when the script begins, and, in particular, MUST NOT change
    as a result of any action, such as "fileinto".
 RFC number: 6785
 Contact address: Sieve mailing list <sieve@ietf.org>

7.3.3. Registration of Sieve Environment Item: imap.changedflags

 Item name: imap.changedflags
 Description: If the script was invoked because of flag changes to an
    existing message, this contains the name(s) of the flag(s) that
    have changed.  Otherwise, the value of this item MUST be the
    empty string.
 RFC number: 6785
 Contact address: Sieve mailing list <sieve@ietf.org>

7.3.4. Registration of Sieve Environment Item: imap.user

 Item name: imap.user
 Description: The identity (IMAP login ID) of the IMAP user that
    caused the action.
 RFC number: 6785
 Contact address: Sieve mailing list <sieve@ietf.org>

7.3.5. Registration of Sieve Environment Item: imap.email

 Item name: imap.email
 Description: The primary email address of the IMAP user that
    caused the action (the user identified by "imap.user").
 RFC number: 6785
 Contact address: Sieve mailing list <sieve@ietf.org>

Leiba Standards Track [Page 17] RFC 6785 IMAP Events in Sieve November 2012

7.4. Registration of IMAP METADATA Mailbox Entry Name

 The following information has been added to the IMAP METADATA Mailbox
 Entry Registry (<http://www.iana.org/assignments/imap-metadata>),
 according to the METADATA extension [RFC5464].
 Type: Mailbox
 Name: /shared/imapsieve/script
 Description: This entry name is used to define mailbox metadata
    associated with IMAP events in Sieve for the associated mailbox.
    Specifically, this specifies the Sieve script that will be invoked
    when IMAP events occur on the specified mailbox.
 Content-type: text/plain; charset=utf-8
 RFC number: 6785
 Contact address: Sieve mailing list <sieve@ietf.org>

7.5. Registration of IMAP METADATA Server Entry Name

 The following information has been added to the IMAP METADATA Server
 Entry Registry (<http://www.iana.org/assignments/imap-metadata>),
 according to the METADATA extension [RFC5464].
 Type: Server
 Name: /shared/imapsieve/script
 Description: This entry name is used to define metadata associated
    globally with IMAP events in Sieve for the associated server.
    Specifically, this specifies the Sieve script that will be invoked
    when IMAP events occur on any mailbox in the server that does not
    have its own mailbox-level /shared/imapsieve/script entry.
 Content-type: text/plain; charset=utf-8
 RFC number: 6785
 Contact address: Sieve mailing list <sieve@ietf.org>

8. References

8.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL -
            VERSION 4rev1", RFC 3501, March 2003.
 [RFC3502]  Crispin, M., "Internet Message Access Protocol (IMAP) -
            MULTIAPPEND Extension", RFC 3502, March 2003.
 [RFC3894]  Degener, J., "Sieve Extension: Copying Without Side
            Effects", RFC 3894, October 2004.

Leiba Standards Track [Page 18] RFC 6785 IMAP Events in Sieve November 2012

 [RFC5183]  Freed, N., "Sieve Email Filtering: Environment Extension",
            RFC 5183, May 2008.
 [RFC5228]  Guenther, P. and T. Showalter, "Sieve: An Email Filtering
            Language", RFC 5228, January 2008.
 [RFC5232]  Melnikov, A., "Sieve Email Filtering: Imap4flags
            Extension", RFC 5232, January 2008.
 [RFC5464]  Daboo, C., "The IMAP METADATA Extension", RFC 5464,
            February 2009.
 [RFC5804]  Melnikov, A. and T. Martin, "A Protocol for Remotely
            Managing Sieve Scripts", RFC 5804, July 2010.
 [RFC6409]  Gellens, R. and J. Klensin, "Message Submission for Mail",
            STD 72, RFC 6409, November 2011.

8.2. Informative References

 [RFC4315]  Crispin, M., "Internet Message Access Protocol (IMAP) -
            UIDPLUS extension", RFC 4315, December 2005.
 [RFC5230]  Showalter, T. and N. Freed, "Sieve Email Filtering:
            Vacation Extension", RFC 5230, January 2008.
 [RFC5235]  Daboo, C., "Sieve Email Filtering: Spamtest and Virustest
            Extensions", RFC 5235, January 2008.
 [RFC5293]  Degener, J. and P. Guenther, "Sieve Email Filtering:
            Editheader Extension", RFC 5293, August 2008.
 [RFC5429]  Stone, A., "Sieve Email Filtering: Reject and Extended
            Reject Extensions", RFC 5429, March 2009.
 [RFC5435]  Melnikov, A., Leiba, B., Segmuller, W., and T. Martin,
            "Sieve Email Filtering: Extension for Notifications",
            RFC 5435, January 2009.
 [RFC5703]  Hansen, T. and C. Daboo, "Sieve Email Filtering: MIME Part
            Tests, Iteration, Extraction, Replacement, and Enclosure",
            RFC 5703, October 2009.

Leiba Standards Track [Page 19] RFC 6785 IMAP Events in Sieve November 2012

Author's Address

 Barry Leiba
 Huawei Technologies
 Phone: +1 646 827 0648
 EMail: barryleiba@computer.org
 URI:   http://internetmessagingtechnology.org/

Leiba Standards Track [Page 20]

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