Internet Engineering Task Force (IETF) A. Melnikov
Request for Comments: 6468 Isode Limited
Category: Standards Track B. Leiba
ISSN: 2070-1721 K. Li
Huawei Technologies
February 2012
Sieve Notification Mechanism: SIP MESSAGE
Abstract
This document describes a profile of the Sieve extension for
notifications, to allow notifications to be sent over SIP MESSAGE.
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/rfc6468.
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.
Melnikov, et al. Standards Track [Page 1]
RFC 6468 Sieve Notification: SIP MESSAGE February 2012
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
2. Definition . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Notify Parameter "method" . . . . . . . . . . . . . . . . 3
2.2. Notify Tag ":from" . . . . . . . . . . . . . . . . . . . . 3
2.3. Notify Tag ":options" . . . . . . . . . . . . . . . . . . 4
2.4. Notify Tag ":importance" . . . . . . . . . . . . . . . . . 4
2.5. Notify tag ":message" . . . . . . . . . . . . . . . . . . 4
2.6. Other Definitions . . . . . . . . . . . . . . . . . . . . 5
2.7. Test notify_method_capability . . . . . . . . . . . . . . 5
3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Requirements Conformance Checklist . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . . 10
1. Introduction
1.1. Overview
The Notify extension [RFC5435] to the Sieve mail filtering language
[RFC5228] is a framework for providing notifications by employing
URIs that specify the notification mechanism. (See RFC 5435 for
details about the motivation and use cases.) This document defines
how Session Initiation Protocol (SIP) URIs [RFC3261] are used to
generate notifications via SIP MESSAGE [RFC3428].
1.2. Terminology
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 RFC 2119 [RFC2119].
This document inherits terminology from the Sieve email filtering
language [RFC5228], the Sieve Notify extension [RFC5435], and RFC
3261 [RFC3261].
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2. Definition
The SIP MESSAGE mechanism defined in this document results in the
sending of a SIP MESSAGE request to notify a recipient about an email
message.
2.1. Notify Parameter "method"
The "method" parameter MUST be a URI that conforms to the SIP or SIPS
URI scheme (as specified in RFC 3261 [RFC3261]) and that identifies a
SIP or SIPS recipient of the notification. The URI MAY include the
resource identifier portion of a SIP address and URI parameters. The
URI MUST include the URI parameter "method", with the value
"MESSAGE". Example:
notify "sip:romeo@example.com;method=MESSAGE"
--------------
Note that future specifications might extend this document and define
Sieve notifications that use SIP methods other than "MESSAGE".
The processing application MUST form a request according to the rules
specified in RFC 3261 [RFC3261].
Note that other URI schemes can also trigger SIP processing, but only
SIP and SIPS are defined here. Future extensions might define other
Sieve notification methods that use SIP through other URI schemes.
2.2. Notify Tag ":from"
The value of the ":from" tag MUST use the SIP "From" header field
syntax; if the ":from" value is specified, has valid syntax, and is
valid according to the implementation-specific security checks (see
Section 3.3 of Sieve Notify [RFC5435]), then the notification SHOULD
include the "From" SIP header field containing the value of the
":from" notify tag. If the specified value is not valid, then it is
ignored.
All SIP authentication, including challenges and client certificates,
SHOULD be done in the context of the Sieve engine -- the Sieve engine
is the identity being authenticated. This avoids security issues
associated with the Sieve engine's having access to the end user's
SIP authentication credentials. The Sieve engine MAY use server-wide
credentials (including applicable certificates) that are the same for
all scripts. Alternatively, it MAY, for auditing purposes, use
different sets of Sieve-engine credentials when operating on behalf
of different users.
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See Section 22 of RFC 3261 [RFC3261] for more information about SIP
authentication.
2.3. Notify Tag ":options"
Handling of the ":options" tag is implementation specific. This
document doesn't require presence of any option and doesn't define
how options are processed.
2.4. Notify Tag ":importance"
The ":importance" tag is intended to convey the importance of the SIP
MESSAGE notification, not the importance of the email message that
generated the notification. The value of the ":importance" tag MAY,
therefore, be transformed into SIP "Priority" header field (in
addition to or instead of including it in the body of the message).
Note that because the Sieve ":importance" tag only has three values,
not all SIP "Priority" values can be represented in the
transformation. If this transformation is done, the value of the
"Priority" header field MUST be "urgent" if the value of the
":importance" tag is "1", "normal" if the value of the ":importance"
tag is "2", and "non-urgent" if the value of the ":importance" tag is
"3". There is no mapping to the SIP value "emergency", nor to any
additional values that might be defined.
2.5. Notify tag ":message"
If the ":message" tag is included, it MUST be transformed into the
message body of a SIP MESSAGE, which MUST have Content-Type value of
"text/plain" with CHARSET="UTF-8". If the ":message" tag is not
included, a default message will be used. The values of the "From"
and "Subject" header fields of the triggering email message are
particularly useful to users receiving notifications, and including
them in the default message is generally a good idea, as shown in
Section 3.2 below. (However, see the Security Considerations,
Section 5.) The default body might also include the value of the
":importance" tag, if one is specified.
Note that in no case is the actual triggering message body included
in the notification.
Implementations MUST comply with the SIP MESSAGE size limits, as
discussed in Section 8 of RFC 3428 [RFC3428].
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2.6. Other Definitions
An implementation MUST ignore any URI parameter it does not
understand (the URI MUST be processed as if the parameter were not
present). The URI "body" parameter can serve the same purpose as the
Sieve ":message" tag, providing the message body of the SIP MESSAGE
request. If both are present at the same time, the Sieve processing
MUST ignore the "body" parameter.
Using the ":message" tag has advantages over using the "body"
parameter. Because the ":message" tag is part of the "notify"
statement syntax, it can be easier to include it in a script, and to
do things such as variable substitutions [RFC5229] with it. It is
also easier to include non-ASCII characters in the ":message" tag
because such characters have to be encoded if they are within URI
parameters, but can be included directly in UTF-8 in Sieve tag
values.
The policy for retrying delivery of failed notifications is specified
in RFC 3261 [RFC3261], according to the SIP error code returned
during an attempt to deliver a SIP notification. In other words,
unlike the situation with some other Sieve notification methods,
retries for SIP MESSAGE notifications are controlled by the
notification protocol itself (SIP).
2.7. Test notify_method_capability
Absent use of SIP extensions such as [RFC3856], it is impossible to
tell in advance whether the notification recipient is online and able
to receive a SIP MESSAGE. Expect the notify_method_capability test
for "online" to frequently return "maybe" for this notification
method.
3. Examples
In the following examples, the sender of the email has an address of
juliet@example.org, the entity to be notified has a SIP address of
<sip:romeo@example.com>, and the notification service has a SIP
address <sip:notifier@example.com>.
3.1. Example 1
The following is a basic Sieve notify action with only a method:
notify "sip:romeo@example.com;method=MESSAGE"
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The resulting SIP MESSAGE request might be as follows:
MESSAGE sip:romeo@example.com SIP/2.0
Via: SIP/2.0/TCP notifier.example.com;branch=z9hG4bK776sgdkse
Max-Forwards: 70
From: sip:notifier@example.com;tag=32328
To: sip:romeo@example.com
Call-ID: asd88asd77a@1.2.3.4
CSeq: 1 MESSAGE
Date: Sat, 13 Nov 2010 23:29:00 GMT
Content-Type: text/plain
Content-Length: 53
<juliet@example.com> wrote: Contact me immediately!
In the example above, the email message was received from
juliet@example.com and had "Subject: Contact me immediately!"
3.2. Example 2
The following is a more advanced Sieve notify action with a method,
importance, subject, and message:
notify :importance "1"
:message "You got new mail!"
"sip:romeo@example.com;method=MESSAGE?subject=SIEVE"
MESSAGE sip:romeo@example.com SIP/2.0
Via: SIP/2.0/TCP notifier.example.com;branch=z9hG4bK776sgdkse
Max-Forwards: 70
From: sip:notifier@example.com;tag=32328
To: sip:romeo@example.com
Subject: SIEVE
Priority: urgent
Call-ID: asd88asd77a@1.2.3.4
CSeq: 1 MESSAGE
Date: Fri, 08 Apr 2011 06:54:00 GMT
Content-Type: text/plain
Content-Length: 19
You got new mail!
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4. Requirements Conformance Checklist
Section 3.8 of Sieve Notify [RFC5435] specifies a set of requirements
for Sieve notification methods. A checklist is provided here to show
conformance of the SIP MESSAGE notification method.
1. No new Sieve tags have been added to the "notify" action.
2. An implementation of the SIP MESSAGE notification method SHOULD
NOT modify the final notification text, except to comply with
SIP MESSAGE length limits. Deployments MAY make operational
decisions about notification text, for reasons such as privacy
and confidentiality. Modification of characters themselves
should not be necessary, since the SIP MESSAGE body is encoded
in UTF-8 [RFC3629].
3. An implementation MAY ignore parameters specified in the
":importance" and ":options" tags.
4. A default message is suggested in Section 2.5.
5. A notification sent via the SIP MESSAGE notification method MAY
include the Date header field containing the date-time of the
moment when the SIP MESSAGE notification was generated.
6. The notification source is identified through the SIP "From:"
header field, via the Sieve Notify ":from" tag (see
Section 2.2).
7. An implementation MUST NOT include any extraneous information
not specified in parameters to the notify action.
8. An implementation MUST ignore any URI parameters it does not
understand (i.e., the URI MUST be processed as if the action or
parameter were not present). See Section 2.6 for more details.
9. The notify_method_capability test for the "online" notification-
capability behaves as described in Section 2.7.
10. The policy for retrying delivery of failed notifications is
specified in RFC 3261 [RFC3261], as noted in Section 2.6.
5. Security Considerations
Depending on the information included, sending a notification can be,
from a confidentiality point of view, comparable to forwarding mail
to the notification recipient. Care must be taken when automatically
forwarding information, such as the sender and the subject of a
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message, to ensure that confidential information is not sent into an
insecure environment or over an insecure channel. Depending upon the
environment, this might entail using SIPS URIs, not sending
information about the subject and/or the sender, or applying
heuristics to the message to determine what may be sent.
As required by RFC 3428, user agents that support the SIP MESSAGE
request MUST implement end-to-end authentication, body integrity, and
body confidentiality mechanisms. At the time of this writing, there
is not widespread deployment of SIP end-to-end security, so there can
be cases where it is not possible to use it, even though it is
implemented on one end. It's important to note that such situations
are open to exposure of user credentials, message content, and other
private information via man-in-the-middle and other passive attacks.
The Sieve Notify extension specifies that notification methods MUST
provide mechanisms for avoiding notification loops. In this case,
the SIP protocol itself prevents loops, and no explicit work is
needed within the notification mechanism. In situations where a SIP
MESSAGE notification can result in an email message that could
generate another SIP MESSAGE notification, loop prevention through
rate detection and limiting might be necessary. An implementation
might detect too many notifications within a given time period, too
many triggered by a particular sender, too many with the same
subject, or the like, and shut off the affected notifications for a
period of time or until manual intervention turns them back on.
If SIP MESSAGE requests might be billed by the message, or the use of
them might deplete a user's quota of messages, notification by this
mechanism can present a situation where someone using a large number
of messages to generate a large number of notifications will cause a
significant expense to the recipient. Because there is no external
way an attacker can tell that this is the case, such an attack would
likely be a random or nuisance attack. Nevertheless, users might be
warned of potential costs when they set up SIP MESSAGE notifications.
Other security considerations given in the Sieve base specification
[RFC5228], the Sieve Notify extension [RFC5435], and RFC 3261
[RFC3261] are also relevant to this document.
6. IANA Considerations
The following template provides the IANA registration of the Sieve
notification mechanism specified in this document. This information
has been added to the list of Sieve notification mechanisms
maintained at <http://www.iana.org/assignments/sieve-notification>.
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To: iana@iana.org
Subject: Registration of new Sieve notification mechanism
Mechanism name: sip-message
Mechanism URI: SIP/SIPS as specified in RFC 3261 [RFC3261]
Mechanism-specific options: none
Standards Track/IESG-approved experimental RFC number: [RFC6468]
Person and email address to contact for further information:
See authors of [RFC6468]
7. Acknowledgements
This document borrows some text from RFC 5437 [RFC5437].
Henning Schulzrinne (hgs@cs.columbia.edu) was a special contributor
to this document, with early work and reviews.
The authors would like to thank Adam Roach and Eric Burger for their
helpful comments. Ben Campbell did a very thorough RAI-team review,
as well as a follow-up review to make sure we resolved all of his
issues satisfactorily. This document was greatly improved by their
input.
Qian Sun contributed text to this document.
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.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3428] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C.,
and D. Gurle, "Session Initiation Protocol (SIP) Extension
for Instant Messaging", RFC 3428, December 2002.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC5228] Guenther, P. and T. Showalter, "Sieve: An Email Filtering
Language", RFC 5228, January 2008.
Melnikov, et al. Standards Track [Page 9]
RFC 6468 Sieve Notification: SIP MESSAGE February 2012
[RFC5435] Melnikov, A., Leiba, B., Segmuller, W., and T. Martin,
"Sieve Email Filtering: Extension for Notifications",
RFC 5435, January 2009.
8.2. Informative References
[RFC3856] Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", RFC 3856, August 2004.
[RFC5229] Homme, K., "Sieve Email Filtering: Variables Extension",
RFC 5229, January 2008.
[RFC5437] Saint-Andre, P. and A. Melnikov, "Sieve Notification
Mechanism: Extensible Messaging and Presence Protocol
(XMPP)", RFC 5437, January 2009.
Authors' Addresses
Alexey Melnikov
Isode Limited
5 Castle Business Village
36 Station Road
Hampton, Middlesex TW12 2BX
UK
EMail: Alexey.Melnikov@isode.com
URI: http://www.melnikov.ca/
Barry Leiba
Huawei Technologies
Phone: +1 646 827 0648
EMail: barryleiba@computer.org
URI: http://internetmessagingtechnology.org/
Kepeng Li
Huawei Technologies
Huawei Base, Bantian, Longgang District
Shenzhen, Guangdong 518129
P.R. China
Phone: +86-755-28974289
EMail: likepeng@huawei.com
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