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Network Working Group P. Saint-Andre
Request for Comments: 5437 Cisco
Category: Standards Track A. Melnikov
Isode Limited
January 2009
Sieve Notification Mechanism:
Extensible Messaging and Presence Protocol (XMPP)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (c) 2009 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.
Abstract
This document describes a profile of the Sieve extension for
notifications, to allow notifications to be sent over the Extensible
Messaging and Presence Protocol (XMPP), also known as Jabber.
Saint-Andre & Melnikov Standards Track [Page 1]
RFC 5437 Sieve Notify Method: XMPP January 2009
Table of Contents
1. Introduction ....................................................3
1.1. Overview ...................................................3
1.2. Terminology ................................................3
2. Definition ......................................................3
2.1. Notify Parameter "method" ..................................3
2.2. Test notify_method_capability ..............................3
2.3. Notify Tag ":from" .........................................4
2.4. Notify Tag ":importance" ...................................4
2.5. Notify Tag ":message" ......................................4
2.6. Notify Tag ":options" ......................................4
2.7. XMPP Syntax ................................................4
3. Examples ........................................................6
3.1. Basic Action ...............................................6
3.2. Action with "body" .........................................7
3.3. Action with "body", ":importance", ":message", and
"subject" ..................................................7
3.4. Action with ":from", ":message", ":importance",
"body", and "subject" ......................................8
4. Requirements Conformance ........................................9
5. Internationalization Considerations ............................10
6. Security Considerations ........................................11
7. IANA Considerations ............................................12
8. References .....................................................12
8.1. Normative References ......................................12
8.2. Informative References ....................................13
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RFC 5437 Sieve Notify Method: XMPP January 2009
1. Introduction
1.1. Overview
The [NOTIFY] extension to the [SIEVE] mail filtering language is a
framework for providing notifications by employing URIs to specify
the notification mechanism. This document defines how xmpp URIs (see
[XMPP-URI]) are used to generate notifications via the Extensible
Messaging and Presence Protocol [XMPP], which is widely implemented
in Jabber instant messaging technologies.
1.2. Terminology
This document inherits terminology from [NOTIFY], [SIEVE], and
[XMPP]. In particular, the terms "parameter" and "tag" are used as
described in [NOTIFY] to refer to aspects of Sieve scripts, and the
term "key" is used as described in [XMPP-URI] to refer to aspects of
an XMPP URI.
The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in [TERMS].
2. Definition
2.1. Notify Parameter "method"
The "method" parameter MUST be a URI that conforms to the xmpp URI
scheme (as specified in [XMPP-URI]) and that identifies an XMPP
account associated with the email inbox. The URI MAY include the
resource identifier of an XMPP address and/or the query component
portion of an XMPP URI, but SHOULD NOT include an authority component
or fragment identifier component. The processing application MUST
extract an XMPP address from the URI in accordance with the
processing rules specified in [XMPP-URI]. The resulting XMPP address
MUST be encapsulated in XMPP syntax as the value of the XMPP 'to'
attribute.
2.2. Test notify_method_capability
In response to a notify_method_capability test for the "online"
notification-capability, an implementation SHOULD return a value of
"yes" if it has knowledge of an active presence session (see
[XMPP-IM]) for the specified XMPP notification-uri; otherwise, it
SHOULD return a value of "maybe" (since typical XMPP systems may not
allow a Sieve engine to gain knowledge about the presence of XMPP
entities).
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RFC 5437 Sieve Notify Method: XMPP January 2009
2.3. Notify Tag ":from"
If included, the ":from" tag MUST be an electronic address that
conforms to the "Mailbox" rule defined in [RFC5321]. The value of
the ":from" tag MAY be included in the human-readable XML character
data of the XMPP notification; alternatively or in addition, it MAY
be transformed into formal XMPP syntax, in which case it MUST be
encapsulated as the value of an XMPP SHIM (Stanza Headers and
Internet Metadata) [SHIM] header named "Resent-From".
2.4. Notify Tag ":importance"
The ":importance" tag has no special meaning for this notification
mechanism, and this specification puts no restriction on its use.
The value of the ":importance" tag MAY be transformed into XMPP
syntax (in addition to or instead of including appropriate text in
the XML character data of the XMPP <body/> element); if so, it SHOULD
be encapsulated as the value of an XMPP SHIM (Stanza Headers and
Internet Metadata) [SHIM] header named "Urgency", where the XML
character of that header is "high" if the value of the ":importance"
tag is "1", "medium" if the value of the ":importance" tag is "2",
and "low" if the value of the ":importance" tag is "3".
2.5. Notify Tag ":message"
If the ":message" tag is included, that string MUST be transformed
into the XML character data of an XMPP <body/> element (where the
string is generated according to the guidelines specified in Section
3.6 of [NOTIFY]).
2.6. Notify Tag ":options"
The ":options" tag has no special meaning for this notification
mechanism. Any handling of this tag is the responsibility of an
implementation.
2.7. XMPP Syntax
The xmpp mechanism results in the sending of an XMPP message to
notify a recipient about an email message. The general XMPP syntax
is as follows:
o The notification MUST be an XMPP <message/> stanza.
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RFC 5437 Sieve Notify Method: XMPP January 2009
o The value of the XMPP 'from' attribute SHOULD be the XMPP address
of the notification service associated with the Sieve engine or
the XMPP address of the entity to be notified. The value of the
XMPP 'from' attribute MUST NOT be generated from the Sieve ":from"
tag.
o The value of the XMPP 'to' attribute MUST be the XMPP address
specified in the XMPP URI contained in the "method" notify
parameter.
o The value of the XMPP 'type' attribute MUST be 'headline' or
'normal'.
o The XMPP <message/> stanza MUST include a <body/> child element.
If the ":message" tag is included in the Sieve script, that string
MUST be used as the XML character data of the <body/> element. If
not and if the XMPP URI contained in the "method" notify parameter
specified a "body" key in the query component, that value SHOULD
be used. Otherwise, the XML character data SHOULD be some
configurable text indicating that the message is a Sieve
notification.
o The XMPP <message/> stanza MAY include a <subject/> child element.
If the XMPP URI contained in the "method" notify parameter
specified a "subject" key in the query component, that value
SHOULD be used as the XML character data of the <subject/>
element. Otherwise, the XML character data SHOULD be some
configurable text indicating that the message is a Sieve
notification.
o The XMPP <message/> stanza SHOULD include a URI, for the recipient
to use as a hint in locating the message, encapsulated as the XML
character data of a <url/> child element of an <x/> element
qualified by the 'jabber:x:oob' namespace, as specified in [OOB].
If included, the URI SHOULD be an Internet Message Access Protocol
[IMAP] URL that specifies the location of the message, as defined
in [IMAP-URL], but MAY be another URI type that can specify or
hint at the location of an email message, such as a URI for an
HTTP resource [HTTP] or a Post Office Protocol Version 3 (POP3)
mailbox [POP-URL] at which the message can be accessed. It is not
expected that an XMPP user agent shall directly handle such a URI,
but instead that it shall invoke an appropriate helper application
to handle the URI.
o The XMPP <message/> stanza MAY include an XMPP SHIM (Stanza
Headers and Internet Metadata) [SHIM] header named "Resent-From".
If the Sieve script included a ":from" tag, the "Resent-From"
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RFC 5437 Sieve Notify Method: XMPP January 2009
value MUST be the value of the ":from" tag; otherwise, the
"Resent-From" value SHOULD be the envelope recipient address of
the original email message that triggered the notification.
3. Examples
In the following examples, the sender of the email has an address of
<mailto:juliet@example.org>, the entity to be notified has an email
address of <mailto:romeo@example.com> and an XMPP address of
romeo@im.example.com (resulting in an XMPP URI of
<xmpp:romeo@im.example.com>), and the notification service associated
with the Sieve engine has an XMPP address of notify.example.com.
Note: In the following examples, line breaks are included in XMPP
URIs solely for the purpose of readability.
3.1. Basic Action
The following is a basic Sieve notify action with only a method. The
XML character data of the XMPP <body/> and <subject/> elements are
therefore generated by the Sieve engine based on configuration. In
addition, the Sieve engine includes a URI pointing to the message.
Basic action (Sieve syntax)
notify "xmpp:romeo@im.example.com"
The resulting XMPP <message/> stanza might be as follows:
Basic action (XMPP syntax)
<message from='notify.example.com'
to='romeo@im.example.com'
type='headline'
xml:lang='en'>
<subject>SIEVE</subject>
<body><juliet@example.com> You got mail.</body>
<x xmlns='jabber:x:oob'>
<url>
imap://romeo@example.com/INBOX;UIDVALIDITY=385759043/;UID=18
</url>
</x>
</message>
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3.2. Action with "body"
The following action contains a "body" key in the query component of
the XMPP URI but no ":message" tag in the Sieve script. As a result,
the XML character data of the XMPP <body/> element in the XMPP
notification is taken from the XMPP URI. In addition, the Sieve
engine includes a URI pointing to the message.
Action with "body" (Sieve syntax)
notify "xmpp:romeo@im.example.com?message
;body=Wherefore%20art%20thou%3F"
The resulting XMPP <message/> stanza might be as follows.
Action with "body" (XMPP syntax)
<message from='notify.example.com'
to='romeo@im.example.com'
type='headline'
xml:lang='en'>
<subject>SIEVE</subject>
<body>Wherefore art thou?</body>
<x xmlns='jabber:x:oob'>
<url>
imap://romeo@example.com/INBOX;UIDVALIDITY=385759044/;UID=19
</url>
</x>
</message>
3.3. Action with "body", ":importance", ":message", and "subject"
The following action specifies an ":importance" tag and a ":message"
tag in the Sieve script, as well as a "body" key and a "subject" key
in the query component of the XMPP URI. As a result, the ":message"
tag from the Sieve script overrides the "body" key from the XMPP URI
when generating the XML character data of the XMPP <body/> element.
In addition, the Sieve engine includes a URI pointing to the message.
Action with "body", ":importance", ":message", and "subject" (Sieve
syntax)
notify :importance "1"
:message "Contact Juliet immediately!"
"xmpp:romeo@im.example.com?message
;body=You%27re%20in%20trouble
;subject=ALERT%21"
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RFC 5437 Sieve Notify Method: XMPP January 2009
The resulting XMPP <message/> stanza might be as follows.
Action with "body", ":importance", ":message", and "subject" (XMPP
syntax)
<message from='notify.example.com'
to='romeo@im.example.com'
type='headline'
xml:lang='en'>
<subject>ALERT!</subject>
<body>Contact Juliet immediately!</body>
<headers xmlns='http://jabber.org/protocol/shim'>
<header name='Urgency'>high</header>
</headers>
<x xmlns='jabber:x:oob'>
<url>
imap://romeo@example.com/INBOX;UIDVALIDITY=385759045/;UID=20
</url>
</x>
</message>
3.4. Action with ":from", ":message", ":importance", "body", and
"subject"
The following action specifies a ":from" tag, an ":importance" tag,
and a ":message" tag in the Sieve script, as well as a "body" key and
a "subject" key in the query component of the XMPP URI. As a result,
the ":message" tag from the Sieve script overrides the "body" key
from the XMPP URI when generating the XML character data of the XMPP
<body/> element. In addition, the Sieve engine includes a URI
pointing to the message, as well as an XMPP SHIM (Stanza Headers and
Internet Metadata) [SHIM] header named "Resent-From" (which
encapsulates the value of the ":from" tag).
Action with ":from", ":importance", ":message", "body", and "subject"
(Sieve syntax)
notify :from "romeo.my.romeo@example.com"
:importance "1"
:message "Contact Juliet immediately!"
"xmpp:romeo@im.example.com?message
;body=You%27re%20in%20trouble
;subject=ALERT%21"
The resulting XMPP <message/> stanza might be as follows.
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RFC 5437 Sieve Notify Method: XMPP January 2009
Action with ":from", ":importance", ":message", "body", and "subject"
(XMPP syntax)
<message from='notify.example.com'
to='romeo@im.example.com'
type='headline'
xml:lang='en'>
<subject>ALERT!</subject>
<body>Contact Juliet immediately!</body>
<headers xmlns='http://jabber.org/protocol/shim'>
<header name='Resent-From'>romeo.my.romeo@example.com</header>
<header name='Urgency'>high</header>
</headers>
<x xmlns='jabber:x:oob'>
<url>
imap://romeo@example.com/INBOX;UIDVALIDITY=385759045/;UID=21
</url>
</x>
</message>
4. Requirements Conformance
Section 3.8 of [NOTIFY] specifies a set of requirements for Sieve
notification methods. The conformance of the xmpp notification
mechanism is provided here.
1. An implementation of the xmpp notification method SHOULD NOT
modify the final notification text (e.g., to limit the length);
however, a given deployment MAY do so (e.g., if recipients pay
per character or byte for XMPP messages). Modification of
characters themselves should not be necessary, since XMPP
character data is encoded in [UTF-8].
2. An implementation MAY ignore parameters specified in the
":from", ":importance", and ":options" tags.
3. There is no recommended default message for an implementation to
include if the ":message" tag is not specified.
4. A notification sent via the xmpp notification method MAY include
a timestamp in the textual message.
5. The value of the XMPP 'from' attribute MUST be the XMPP address
of the notification service associated with the Sieve engine.
The value of the Sieve ":from" tag MAY be transformed into the
value of an XMPP SHIM (Stanza Headers and Internet Metadata)
[SHIM] header named "Resent-From".
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6. The value of the XMPP 'to' attribute MUST be the XMPP address
specified in the XMPP URI contained in the "method" parameter.
7. In accordance with [XMPP-URI], an implementation MUST ignore any
URI action or key it does not understand (i.e., the URI MUST be
processed as if the action or key were not present). It is
RECOMMENDED to support the XMPP "message" query type (see
[QUERIES]) and the associated "body" and "subject" keys, which
SHOULD be mapped to the XMPP <body/> and <subject/> child
elements of the XMPP <message/> stanza, respectively. However,
if included, then the Sieve notify ":message" tag MUST be mapped
to the XMPP <body/> element, overriding the "body" key (if any)
included in the XMPP URI.
8. An implementation MUST NOT include any other extraneous
information not specified in parameters to the notify action.
9. In response to a notify_method_capability test for the "online"
notification-capability, an implementation SHOULD return a value
of "yes" if it has knowledge of an active presence session (see
[XMPP-IM]) for the specified XMPP notification-uri, but only if
the entity that requested the test is authorized to know the
presence of the associated XMPP entity (e.g., via explicit
presence subscription as specified in [XMPP-IM]); otherwise, it
SHOULD return a value of "maybe" (since typical XMPP systems may
not allow a Sieve engine to gain knowledge about the presence of
XMPP entities).
10. An implementation SHOULD NOT attempt to retry delivery of a
notification if it receives an XMPP error of type "auth" or
"cancel", MAY attempt to retry delivery if it receives an XMPP
error of type "wait", and MAY attempt to retry delivery if it
receives an XMPP error of "modify", but only if it makes
appropriate modifications to the notification (see [XMPP]); in
any case, the number of retries SHOULD be limited to a
configurable number no less than 3 and no more than 10. An
implementation MAY throttle notifications if the number of
notifications within a given time period becomes excessive
according to local service policy. Duplicate suppression (if
any) is a matter of implementation and is not specified herein.
5. Internationalization Considerations
Although an XMPP address may contain nearly any [UNICODE] character,
the value of the "method" parameter MUST be a Uniform Resource
Identifier (see [URI]) rather than an Internationalized Resource
Identifier (see [IRI]). The rules specified in [XMPP-URI] MUST be
followed when generating XMPP URIs.
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RFC 5437 Sieve Notify Method: XMPP January 2009
In accordance with Section 13 of RFC 3920, all data sent over XMPP
MUST be encoded in [UTF-8].
6. Security Considerations
Depending on the information included, sending a notification can be
comparable to forwarding mail to the notification recipient. Care
must be taken when forwarding mail automatically, to ensure that
confidential information is not sent into an insecure environment.
In particular, implementations MUST conform to the security
considerations given in [NOTIFY], [SIEVE], and [XMPP].
[NOTIFY] specifies that a notification method MUST provide mechanisms
for avoiding notification loops. One type of notification loop can
be caused by message forwarding; however, such loops are prevented
because XMPP does not support the forwarding of messages from one
XMPP address to another. Another type of notification loop can be
caused by auto-replies to XMPP messages received by the XMPP
notification service associated with the Sieve engine; therefore,
such a service MUST NOT auto-reply to XMPP messages it receives.
A common use case might be for a user to create a script that enables
the Sieve engine to act differently if the user is currently
available at a particular type of service (e.g., send notifications
to the user's XMPP address if the user has an active session at an
XMPP service). Whether the user is currently available can be
determined by means of a notify_method_capability test for the
"online" notification-capability. In XMPP, information about current
network availability is called "presence" (see also [MODEL]). Since
[XMPP-IM] requires that a user must approve a presence subscription
before an entity can gain access to the user's presence information,
a limited but reasonably safe implementation might be for the Sieve
engine to request a subscription to the user's presence. The user
would then need to approve that subscription request so that the
Sieve engine can act appropriately depending on whether the user is
online or offline. However, the Sieve engine MUST NOT use the user's
presence information when processing scripts on behalf of a script
owner other than the user, unless the Sieve engine has explicit
knowledge (e.g., via integration with an XMPP server's presence
authorization rules) that the script owner is authorized to know the
user's presence. While it would be possible to design a more
advanced approach to the delegation of presence authorization, any
such approach is left to future standards work.
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RFC 5437 Sieve Notify Method: XMPP January 2009
7. IANA Considerations
The following template provides the IANA registration of the Sieve
notification mechanism specified in this document:
To: iana@iana.org
Subject: Registration of new Sieve notification mechanism
Mechanism name: xmpp
Mechanism URI: RFC 5122 [XMPP-URI]
Mechanism-specific options: none
Permanent and readily available reference: RFC 5437
Person and email address to contact for further information:
Peter Saint-Andre <registrar@xmpp.org>
This information has been added to the list of Sieve notification
mechanisms maintained at <http://www.iana.org>.
8. References
8.1. Normative References
[NOTIFY] Melnikov, A., Ed., Leiba, B., Ed., Segmuller, W., and T.
Martin, "Sieve Email Filtering: Extension for
Notifications", RFC 5435, January 2009.
[OOB] Saint-Andre, P., "Out of Band Data", XSF XEP 0066,
August 2006.
[QUERIES] Saint-Andre, P., "XMPP URI Scheme Query Components", XSF
XEP 0147, September 2006.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008.
[SHIM] Saint-Andre, P. and J. Hildebrand, "Stanza Headers and
Internet Metadata", XSF XEP 0131, July 2006.
[SIEVE] Guenther, P., Ed. and T. Showalter, Ed., "Sieve: An Email
Filtering Language", RFC 5228, January 2008.
[TERMS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[XMPP-URI] Saint-Andre, P., "Internationalized Resource Identifiers
(IRIs) and Uniform Resource Identifiers (URIs) for the
Extensible Messaging and Presence Protocol (XMPP)",
RFC 5122, February 2008.
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8.2. Informative References
[HTTP] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[IMAP] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
[IMAP-URL] Melnikov, A. and C. Newman, "IMAP URL Scheme", RFC 5092,
November 2007.
[IRI] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[MODEL] Day, M., Rosenberg, J., and H. Sugano, "A Model for
Presence and Instant Messaging", RFC 2778, February 2000.
[POP-URL] Gellens, R., "POP URL Scheme", RFC 2384, August 1998.
[UNICODE] The Unicode Consortium, "The Unicode Standard, Version
3.2.0", 2000.
The Unicode Standard, Version 3.2.0 is defined by The
Unicode Standard, Version 3.0 (Reading, MA, Addison-
Wesley, 2000. ISBN 0-201-61633-5), as amended by the
Unicode Standard Annex #27: Unicode 3.1
(http://www.unicode.org/reports/tr27/) and by the Unicode
Standard Annex #28: Unicode 3.2
(http://www.unicode.org/reports/tr28/).
[URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[XMPP] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004.
[XMPP-IM] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
RFC 3921, October 2004.
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Authors' Addresses
Peter Saint-Andre
Cisco
EMail: psaintan@cisco.com
Alexey Melnikov
Isode Limited
EMail: Alexey.Melnikov@isode.com
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