RFC6785: Support for Internet Message Access Protocol (IMAP) Events in Sieve
Download in PDF format Download in text format
Related keywords:
(email)
(filtering)
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.
Leiba Standards Track [Page 13]
RFC 6785 IMAP Events in Sieve November 2012
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";
}
Leiba Standards Track [Page 14]
RFC 6785 IMAP Events in Sieve November 2012
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]