Sieve Notification Mechanism: Extensible Messaging and Presence Protocol (XMPP)
RFC 5437

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
Saint-Andre & Melnikov Standards Track [Page 2]
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).
Saint-Andre & Melnikov Standards Track [Page 3]
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.
Saint-Andre & Melnikov Standards Track [Page 4]
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"
Saint-Andre & Melnikov Standards Track [Page 5]
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>&lt;juliet@example.com&gt; You got mail.</body>
 <x xmlns='jabber:x:oob'>
 <url>
 imap://romeo@example.com/INBOX;UIDVALIDITY=385759043/;UID=18
 </url>
 </x>
 </message>
Saint-Andre & Melnikov Standards Track [Page 6]
RFC 5437 Sieve Notify Method: XMPP January 2009
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"
Saint-Andre & Melnikov Standards Track [Page 7]
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.
Saint-Andre & Melnikov Standards Track [Page 8]
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".
Saint-Andre & Melnikov Standards Track [Page 9]
RFC 5437 Sieve Notify Method: XMPP January 2009
 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.
Saint-Andre & Melnikov Standards Track [Page 10]
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.
Saint-Andre & Melnikov Standards Track [Page 11]
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.
Saint-Andre & Melnikov Standards Track [Page 12]
RFC 5437 Sieve Notify Method: XMPP January 2009
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.
Saint-Andre & Melnikov Standards Track [Page 13]
RFC 5437 Sieve Notify Method: XMPP January 2009
Authors' Addresses
 Peter Saint-Andre
 Cisco
 EMail: psaintan@cisco.com
 Alexey Melnikov
 Isode Limited
 EMail: Alexey.Melnikov@isode.com
Saint-Andre & Melnikov Standards Track [Page 14]