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rfc:rfc5435

Network Working Group A. Melnikov, Ed. Request for Comments: 5435 Isode Limited Category: Standards Track B. Leiba, Ed.

                                                          W. Segmuller
                                       IBM T.J. Watson Research Center
                                                             T. Martin
                                                     Endless Crossword
                                                          January 2009
         Sieve Email Filtering: Extension for Notifications

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

 Users go to great lengths to be notified as quickly as possible that
 they have received new mail.  Most of these methods involve polling
 to check for new messages periodically.  A push method handled by the
 final delivery agent gives users quicker notifications and saves
 server resources.  This document does not specify the notification
 method, but it is expected that using existing instant messaging
 infrastructure such as Extensible Messaging and Presence Protocol
 (XMPP), or Global System for Mobile Communications (GSM) Short
 Message Service (SMS) messages will be popular.  This document
 describes an extension to the Sieve mail filtering language that
 allows users to give specific rules for how and when notifications
 should be sent.

Melnikov, et al. Standards Track [Page 1] RFC 5435 Sieve Extension: Notifications January 2009

Table of Contents

 1. Introduction ....................................................3
    1.1. Conventions Used in This Document ..........................3
 2. Capability Identifier ...........................................3
 3. Notify Action ...................................................3
    3.1. Notify Action Syntax and Semantics .........................3
    3.2. Notify Parameter "method" ..................................3
    3.3. Notify Tag ":from" .........................................4
    3.4. Notify Tag ":importance" ...................................4
    3.5. Notify Tag ":options" ......................................5
    3.6. Notify Tag ":message" ......................................5
    3.7. Examples ...................................................6
    3.8. Requirements on Notification Methods Specifications ........7
 4. Test valid_notify_method ........................................8
 5. Test notify_method_capability ...................................9
 6. Modifier encodeurl to the 'set' Action .........................10
 7. Interactions with Other Sieve Actions ..........................11
 8. Security Considerations ........................................11
 9. IANA Considerations ............................................13
    9.1. Registration of Sieve Extension ...........................13
    9.2. New Registry for Sieve Notification Mechanisms ............14
    9.3. New Registry for Notification-Capability Parameters .......14
 10. Acknowledgements ..............................................15
 11. References ....................................................16
    11.1. Normative References .....................................16
    11.2. Informative References ...................................16

Melnikov, et al. Standards Track [Page 2] RFC 5435 Sieve Extension: Notifications January 2009

1. Introduction

 This is an extension to the Sieve language defined by [Sieve] for
 providing instant notifications.  It defines the new action "notify".
 This document does not specify the notification methods.  Examples of
 possible notification methods are email and XMPP.  To allow for the
 portability of scripts that use notifications, implementation of the
 [MailTo] method is mandatory.  Other available methods shall depend
 upon the implementation and configuration of the system.

1.1. Conventions Used in This Document

 Conventions for notations are as in [Sieve], Section 1.1, including
 the use of [ABNF].
 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 [Kwds].

2. Capability Identifier

 The capability string associated with the extension defined in this
 document is "enotify".

3. Notify Action

3.1. Notify Action Syntax and Semantics

 Usage:  notify [":from" string]
         [":importance" <"1" / "2" / "3">]
         [":options" string-list]
         [":message" string]
         <method: string>
 The "notify" action specifies that a notification should be sent to a
 user.  The format of the notification is implementation-defined and
 is also affected by the notification method used (see Section 3.2).
 However, all content specified in the ":message" parameter SHOULD be
 included.

3.2. Notify Parameter "method"

 The "method" positional parameter identifies the notification method
 that will be used; it is a URI [URI].  For example, the notification
 method can be a tel URI [TEL-URI] with a phone number to send SMS
 messages to, or an XMPP [XMPP] URI containing an XMPP identifier
 [XMPP-URI].

Melnikov, et al. Standards Track [Page 3] RFC 5435 Sieve Extension: Notifications January 2009

 The supported URI values will be site-specific, but support for the
 [MailTo] method is REQUIRED in order to ensure interoperability.  If
 a URI schema is specified that the implementation does not support,
 the notification MUST cause an error condition at run time.  Sieve
 scripts can check the supported methods using the valid_notify_method
 test to be sure that they only use supported ones, to avoid such
 error conditions.
 If the "method" parameter contains a supported URI schema, then the
 URI MUST be checked for syntactic validity.  Invalid URI syntax or an
 unsupported URI extension MUST cause an error.  An implementation MAY
 enforce other semantic restrictions on URIs -- for example, to
 restrict phone numbers in a tel: URI to a particular geographical
 region -- and will treat violations of such semantic restrictions as
 errors.

3.3. Notify Tag ":from"

 A ":from" tag may be used to specify an author of the notification.
 The syntax of this parameter's value is method-specific.
 Implementations SHOULD check the syntax according to the notification
 method specification and generate an error when a syntactically
 invalid ":from" tag is specified.
 In order to minimize/prevent forgery of the author value,
 implementations SHOULD impose restrictions on what values can be
 specified in a ":from" tag.  For example, an implementation may
 restrict this value to be a member of a list of known author
 addresses or to belong to a particular domain.  It is suggested that
 values that don't satisfy such restrictions simply be ignored rather
 than causing the "notify" action to fail.

3.4. Notify Tag ":importance"

 The ":importance" tag specifies the importance of quick delivery of
 the notification, as perceived by the Sieve script owner.  The
 ":importance" tag is followed by a numeric value represented as a
 string: "1" (high importance), "2" (normal importance), and "3" (low
 importance).  If no importance is given, the default value "2" SHOULD
 be assumed.  A notification method MAY treat the importance value as
 a transport indicator.  For example, it might deliver notifications
 of high importance quicker than notifications of normal or low
 importance.  Some notification methods allow users to specify their
 state of activity (for example, "busy" or "away from keyboard").  If
 the notification method provides this information, it SHOULD be used
 to selectively send notifications.  If, for example, the user marks

Melnikov, et al. Standards Track [Page 4] RFC 5435 Sieve Extension: Notifications January 2009

 herself as "busy", a notification method can require that a
 notification with importance of "3" is not to be sent; however, the
 user might be notified of a notification with higher importance.
 If the notification method allows users to filter messages based upon
 certain parameters in the message, users SHOULD be able to filter
 based upon importance.  If the notification method does not support
 importance, then this parameter MUST be ignored.  An implementation
 MAY include the importance value in the default message, Section 3.6,
 if one is not provided.

3.5. Notify Tag ":options"

 The ":options" tag is used to send additional parameters to the
 notification method.  Interpretation of the parameters is method-
 specific.  This document doesn't specify any such additional
 parameter.
 Each string in the options string list has the following syntax:
 "<optionname>=<value>"
 where optionname has the following ABNF [ABNF]:
    l-d = ALPHA / DIGIT
    l-d-p = l-d / "." / "-" / "_"
    optionname = l-d *l-d-p
    value = *(%x01-09 / %x0B-0C / %x0E-FF)

3.6. Notify Tag ":message"

 The ":message" tag specifies the message data to be included in the
 notification.  The entirety of the string SHOULD be sent, but
 implementations MAY shorten the message for technical or aesthetic
 reasons.  If the ":message" parameter is absent, a default
 implementation-specific message is used.  Unless otherwise specified
 by a particular notification mechanism, an implementation default
 containing at least the value of the "From" header field and the
 value of the "Subject" header field is RECOMMENDED.
 In order to construct more complex messages, the notify extension can
 be used together with the Sieve variables extension [Variables], as
 shown in the examples below.

Melnikov, et al. Standards Track [Page 5] RFC 5435 Sieve Extension: Notifications January 2009

3.7. Examples

 Example 1:
     require ["enotify", "fileinto", "variables"];
     if header :contains "from" "boss@example.org" {
         notify :importance "1"
             :message "This is probably very important"
                         "mailto:alm@example.com";
         # Don't send any further notifications
         stop;
     }
     if header :contains "to" "sievemailinglist@example.org" {
         # :matches is used to get the value of the Subject header
         if header :matches "Subject" "*" {
             set "subject" "${1}";
         }
         # :matches is used to get the value of the From header
         if header :matches "From" "*" {
             set "from" "${1}";
         }
         notify :importance "3"
             :message "[SIEVE] ${from}: ${subject}"
             "mailto:alm@example.com";
         fileinto "INBOX.sieve";
     }
 Example 2:
     require ["enotify", "fileinto", "variables", "envelope"];
     if header :matches "from" "*@*.example.org" {
         # :matches is used to get the MAIL FROM address
         if envelope :all :matches "from" "*" {
             set "env_from" " [really: ${1}]";
         }
         # :matches is used to get the value of the Subject header
         if header :matches "Subject" "*" {
             set "subject" "${1}";
         }
         # :matches is used to get the address from the From header
         if address :matches :all "from" "*" {
             set "from_addr" "${1}";
         }

Melnikov, et al. Standards Track [Page 6] RFC 5435 Sieve Extension: Notifications January 2009

         notify :message "${from_addr}${env_from}: ${subject}"
                         "mailto:alm@example.com";
     }

Example 3:

   require ["enotify", "variables"];
   set "notif_method"
   "xmpp:tim@example.com?message;subject=SIEVE;body=You%20got%20mail";
   if header :contains "subject" "Your dog" {
       set "notif_method" "tel:+14085551212";
   }
   if header :contains "to" "sievemailinglist@example.org" {
       set "notif_method" "";
   }
   if not string :is "${notif_method}" "" {
       notify "${notif_method}";
   }
   if header :contains "from" "boss@example.org" {
       # :matches is used to get the value of the Subject header
       if header :matches "Subject" "*" {
           set "subject" "${1}";
       }
       # don't need high importance notification for
       # a 'for your information'
       if not header :contains "subject" "FYI:" {
           notify :importance "1" :message "BOSS: ${subject}"
                              "tel:+14085551212";
       }
   }

3.8. Requirements on Notification Methods Specifications

 This section describes requirements for documents that define
 specific Sieve notification methods.
 Notification mechanisms MUST NOT add new Sieve tags to the "notify"
 action.
 A notification method MAY allow modification of the final
 notification text -- for example, truncating it if it exceeds a
 length limit or modifying characters that can not be represented in
 the target character set.  Characters in the notification text that

Melnikov, et al. Standards Track [Page 7] RFC 5435 Sieve Extension: Notifications January 2009

 can't be represented by the notification method SHOULD be replaced
 with a symbol indicating an unknown character.  Allowed modifications
 MUST be documented in the document describing the notification
 method.
 A notification method MAY ignore parameters specified in the "notify"
 action.
 A notification method MAY recommend the default message value to be
 used if the ":message" argument is not specified.
 Notifications SHOULD include timestamps, if the notification method
 allows for their transmission outside of the textual message.
 Implementation methods that can only transmit timestamps in the
 textual message MAY include them in the textual message.
 A notification MUST include means to identify/track its origin in
 order to allow a recipient to stop notifications or find out how to
 contact the sender.  This requirement is to help with tracking a
 misconfigured or abusive origin of notifications.
 Methods SHOULD NOT include any other extraneous information not
 specified in parameters to the "notify" action.
 Methods MUST specify which URI parameters (if any) must be ignored,
 which ones must be used in the resulting notification, and which ones
 must cause an error.
 Methods MUST specify what values are returned by the
 notify_method_capability test, Section 5, in particular for the
 "online" notification-capability.
 If there are errors sending the notification, the Sieve interpreter
 SHOULD ignore the notification and not retry indefinitely.  The Sieve
 interpreter MAY throttle notifications; if it does, a request to send
 a notification MAY be silently ignored.  Documents describing
 notification methods SHOULD describe how retries, throttling,
 duplicate suppression (if any), etc. are to be handled by
 implementations.

4. Test valid_notify_method

 Usage:  valid_notify_method <notification-uris: string-list>
 The valid_notify_method test is true if the notification methods
 listed in the notification-uris argument are supported and they are
 valid both syntactically (including URI parameters) and semantically

Melnikov, et al. Standards Track [Page 8] RFC 5435 Sieve Extension: Notifications January 2009

 (including implementation-specific semantic restrictions).  This test
 MUST perform exactly the same validation as would be performed on the
 "method" parameter to the "notify" action.
 The test is true only if ALL of the listed notification methods are
 supported and valid.
 Example 4 (partial):
           if not valid_notify_method ["mailto:",
                   "http://gw.example.net/notify?test"] {
               stop;
           }

5. Test notify_method_capability

 Usage:  notify_method_capability [COMPARATOR] [MATCH-TYPE]
         <notification-uri: string>
         <notification-capability: string>
         <key-list: string-list>
 The notify_method_capability test retrieves the notification
 capability specified by the notification-capability string that is
 specific to the notification-uri and matches it to the values
 specified in the key-list.  The test succeeds if a match occurs.  The
 type of match defaults to ":is", and the default comparator is
 "i;ascii-casemap".
 The notification-capability parameter is case insensitive.
 The notify_method_capability test MUST fail unconditionally if the
 specified notification-uri is syntactically invalid (as determined by
 the valid_notify_method test, Section 4) or specifies an unsupported
 notification method.  However this MUST NOT cause an error.
 The notify_method_capability test MUST fail unconditionally if the
 specified notification-capability item is not known to the Sieve
 interpreter.  A script MUST NOT fail with an error if the item does
 not exist.  This allows scripts to be written that handle nonexistent
 items gracefully.
 This document defines a single notification-capability value
 "online", which is described below.  Additional notification-
 capability values may be defined by using the procedure defined in
 Section 9.3.
 The "relational" extension [Relational] adds a match type called
 ":count".  The count of an notify_method_capability test is 0, if the
 returned information is the empty string, or 1.

Melnikov, et al. Standards Track [Page 9] RFC 5435 Sieve Extension: Notifications January 2009

 For the "online" notification-capability, the
 notify_method_capability test can match one of the following key-list
 values:
 o  "yes" - the entity identified by the notification-uri can receive
    a notify notification immediately.  Note that even after this
    value is returned, there is no guarantee that the entity would
    actually be able to receive any notification immediately or even
    receive it at all.  Transport errors, recipient policy, etc. can
    prevent that.
 o  "no" - the entity identified by the notification-uri is not
    currently available to receive an immediate notification.
 o  "maybe" - the Sieve interpreter can't determine if the entity
    identified by the notification-uri is online or not.
 Example 5:
           require ["enotify"];
           if notify_method_capability
                  "xmpp:tim@example.com?message;subject=SIEVE"
                  "Online"
                  "yes" {
               notify :importance "1" :message "You got mail"
                    "xmpp:tim@example.com?message;subject=SIEVE";
           } else {
               notify :message "You got mail" "tel:+14085551212";
           }

6. Modifier encodeurl to the 'set' Action

 Usage:  ":encodeurl"
 When the Sieve script specifies both "variables" [Variables] and
 "enotify" capabilities in the "require", a new "set" action modifier
 (see [Variables]) ":encodeurl" becomes available to Sieve scripts.
 This modifier performs percent-encoding of any octet in the string
 that doesn't belong to the "unreserved" set (see [URI]).  The
 percent-encoding procedure is described in [URI].
 The ":encodeurl" modifier has precedence 15.

Melnikov, et al. Standards Track [Page 10] RFC 5435 Sieve Extension: Notifications January 2009

 Example 6:
     require ["enotify", "variables"];
     set :encodeurl "body_param" "Safe body&evil=evilbody";
     notify "mailto:tim@example.com?body=${body_param}";

7. Interactions with Other Sieve Actions

 The "notify" action is compatible with all other actions, and does
 not affect the operation of other actions.  In particular, the
 "notify" action MUST NOT cancel the implicit keep.
 Multiple executed "notify" actions are allowed.  Specific
 notification methods MAY allow multiple notifications from the same
 script to be collapsed into one.

8. Security Considerations

 Security considerations are discussed in [Sieve].  Additionally,
 implementations must be careful to follow the security considerations
 of the specific notification methods.
 The "notify" action is potentially very dangerous.  The path the
 notification takes through the network may not be secure.  An error
 in the options string may cause the message to be transmitted to
 someone it was not intended for, or may expose information to
 eavesdroppers.
 Just because a notification is received doesn't mean that it was sent
 by the Sieve implementation.  It might be possible to forge
 notifications or modify parts of valid notifications with some
 notification methods.
 Forgery of the ":importance" value (for example, by unauthorized
 script modification) can potentially result in slowdown in
 notification delivery.
 Note that some components of notifications should not be trusted.
 For example, the timestamp field can be easily forged or modified
 when some notification transports are used.  Even if the timestamp is
 believed to be correct by the sender and is not modified in transit,
 it might be misleading on the receiving system due to clock
 differences.

Melnikov, et al. Standards Track [Page 11] RFC 5435 Sieve Extension: Notifications January 2009

 An organization may have a policy about the forwarding of classified
 information to unclassified networks.  Unless the policy is also
 enforced in the module responsible for the generating (or sending) of
 notifications, users can use the extension defined in this document
 to extract classified information and bypass the policy.
 Notifications can result in loops and bounces.  Also, allowing a
 single script to notify multiple destinations can be used as a means
 of amplifying the number of messages in an attack.  Moreover, if loop
 detection is not properly implemented, it may be possible to set up
 exponentially growing notification loops.  Accordingly, Sieve
 notification methods:
 1.  MUST provide mechanisms for avoiding notification loops.
 2.  MUST provide the means for administrators to limit the ability of
     users to abuse notify.  In particular, it MUST be possible to
     limit the number of "notify" actions a script can perform.
     Additionally, if no use cases exist for using "notify" with
     multiple destinations, this limit SHOULD be set to 1.  Additional
     limits, such as the ability to restrict "notify" to local users,
     MAY also be implemented.
 3.  MUST provide facilities to log the use of "notify" in order to
     facilitate tracking down abuse.
 4.  MAY use script analysis to determine whether or not a given
     script can be executed safely.  While the Sieve language is
     sufficiently complex so that full analysis of all possible
     scripts is computationally infeasible, the majority of real-world
     scripts are amenable to analysis.  For example, an implementation
     might allow scripts that it has determined to be safe to run
     unhindered, block scripts that are potentially problematic, and
     subject unclassifiable scripts to additional auditing and
     logging.
 Allowing "notify" action at all may not be appropriate in situations
 where Sieve scripts are associated with email accounts that are
 freely-available and/or not trackable to a human who can be held
 accountable for creating message bombs or other abuse.
 Implementations that construct URIs internally from various notify
 parameters MUST make sure that all components of such URIs are
 properly percent-encoded (see [URI]).  In particular, this applies to
 values of the ":from" and ":message" tagged arguments and may apply
 to the ":options" values.

Melnikov, et al. Standards Track [Page 12] RFC 5435 Sieve Extension: Notifications January 2009

 Header/envelope tests [Sieve], together with Sieve variables, can be
 used to extract the list of users to receive notifications from the
 incoming email message or its envelope.  This is potentially quite
 dangerous, as this can be used for denial-of-service attacks on
 recipients controlled by the message sender.  For this reason,
 implementations SHOULD NOT allow the use of variables containing
 values extracted from the email message in the "method" parameter to
 the "notify" action.  Note that violation of this SHOULD NOT may
 result in the creation of an open relay, i.e., any sender would be
 able to create specially crafted email messages that would result in
 notifications delivered to recipients under the control of the
 sender.  In the worst case, this might result in financial loss by
 the user controlling the Sieve script and/or by recipients of
 notifications (e.g., if a notification is an SMS message).
 Note that the last SHOULD NOT is not a generic prohibition of use of
 variables in the "notify" action, as controlling the target of a
 notification by extracting it from user-owned data stores (such as
 user's Lightweight Directory Access Protocol (LDAP) entry) is
 considered to be useful.
 It is imperative that whatever implementations use to store the user-
 defined filtering scripts protect them from unauthorized
 modification, to preserve the integrity of the mail system.  An
 attacker who can modify a script can cause mail to be discarded,
 rejected, or forwarded to an unauthorized recipient.  In addition,
 it's possible that Sieve scripts might expose private information,
 such as mailbox names or email addresses of favored (or disfavored)
 correspondents.  Because of that, scripts SHOULD also be protected
 from unauthorized retrieval.

9. IANA Considerations

9.1. Registration of Sieve Extension

 To:  iana@iana.org
 Subject:  Registration of new Sieve extension
 Capability name:  enotify
 Description:  adds the "notify" action for notifying user about the
    received message.  It also provides two new tests:
       valid_notify_method checks notification URIs for validity;
       notify_method_capability can check recipients capabilities.
 RFC number:  this RFC
 Contact address:  The Sieve discussion list
    <ietf-mta-filters@imc.org>
 This information has been added to the list of Sieve extensions
 available from http://www.iana.org/.

Melnikov, et al. Standards Track [Page 13] RFC 5435 Sieve Extension: Notifications January 2009

9.2. New Registry for Sieve Notification Mechanisms

 IANA has created a new registry for Sieve notification mechanisms.
 This registry contains both vendor-controlled notification mechanism
 names (beginning with "vnd.") and IETF-controlled notification
 mechanism names.  Vendor-controlled notification mechanism names have
 the format as defined in the following paragraph and may be
 registered on a "First Come First Served" basis [IANA-GUIDELINES], by
 applying to IANA with the form specified later in this section.
 Registration of notification mechanisms that do not begin with "vnd."
 are registered using a "Specification Required" policy
 [IANA-GUIDELINES].
 Vendor-controlled notification mechanism names MUST have the form
 "vnd.<vendor-name>.<mechanism-name>", where <vendor-name> is as
 specified in the Application Configuration Access Protocol (ACAP)
 Vendor Subtree registry [ACAP].
 This defines the template for a new registry for Sieve notification
 mechanisms, which has been created and is available from
 http://www.iana.org/.  There are no initial entries for this
 registry.
 To:  iana@iana.org
 Subject:  Registration of new Sieve notification mechanism
 Mechanism name:  [the name of the mechanism]
 Mechanism URI:  [the RFC number of the document that defines the URI
    used by this mechanism.  Different mechanisms MUST use different
    URI schema.]
 Mechanism-specific options:  [the names of any Sieve notify options
    (as used in the ":options" parameter) that are specific to this
    mechanism, or "none"]
 Permanent and readily available reference:  [the RFC number or an URL
    of the document that defines this notification mechanism]
 Person and email address to contact for further information:  [the
    name and email address of the technical contact for information
    about this mechanism]

9.3. New Registry for Notification-Capability Parameters

 IANA has created a new registry for the notification-capability
 parameters of the notify_method_capability test.  This registry
 contains both vendor-controlled notification-capability values
 (beginning with "vnd.") and IETF-controlled notification-capability
 values.  Vendor-controlled notification-capability values have the
 format as defined in the following paragraph and may be registered on
 a "First Come First Served" basis [IANA-GUIDELINES], by applying to
 IANA with the form specified later in this section.  Registration of

Melnikov, et al. Standards Track [Page 14] RFC 5435 Sieve Extension: Notifications January 2009

 notification-capability values that do not begin with "vnd." are
 registered using the "Specification Required" policy
 [IANA-GUIDELINES].
 Vendor-controlled notification-capability values MUST have the form
 "vnd.<vendor-name>.<capability-name>", where <vendor-name> is as
 specified in the ACAP Vendor Subtree registry [ACAP].
 The following template must be used for registering notification-
 capability parameters:
 To:  iana@iana.org
 Subject:  Registration of a new notification-capability parameter
 Capability name:  [the name of the notification-capability]
 Description:  [an explanation of the purpose of the notification-
    capability]
 Syntax:  [formal definition of allowed values and their syntax]
 Permanent and readily available reference(s):  [the RFC number(s) or
    an URL of the document that defines this notification mechanism]
 Contact information:  [the name and email address of the technical
    contact for information about this mechanism]
 Below is the registration form for the "online" notification-
 capability:
 To:  iana@iana.org
 Subject:  Registration of a new notification-capability parameter
 Capability name:  online
 Description:  Returns whether the entity identified by the
    notification-uri parameter to the notify_method_capability test
    can receive a notify notification immediately.
 Syntax:  Can contain one of three values: "yes", "no", and, "maybe".
    Values MUST be in lowercase.
 Permanent and readily available reference(s):  This RFC
 Contact information:  The Sieve discussion list
    <ietf-mta-filters@imc.org>

10. Acknowledgements

 Thanks to Larry Greenfield, Sarah Robeson, Tim Showalter, Cyrus
 Daboo, Nigel Swinson, Kjetil Torgrim Homme, Michael Haardt, Mark E.
 Mallett, Ned Freed, Lisa Dusseault, Dilyan Palauzov, Arnt
 Gulbrandsen, Peter Saint-Andre, Sean Turner, Cullen Jennings, and
 Pasi Eronen for help with this document.

Melnikov, et al. Standards Track [Page 15] RFC 5435 Sieve Extension: Notifications January 2009

11. References

11.1. Normative References

 [ABNF]             Crocker, D., Ed. and P. Overell, "Augmented BNF
                    for Syntax Specifications: ABNF", STD 68,
                    RFC 5234, January 2008.
 [Kwds]             Bradner, S., "Key words for use in RFCs to
                    Indicate Requirement Levels", BCP 14, RFC 2119,
                    March 1997.
 [MailTo]           Leiba, B. and M. Haardt, "Sieve Notification
                    Mechanism: mailto", RFC 5436, January 2009.
 [Relational]       Segmuller, W. and B. Leiba, "Sieve Extension:
                    Relational Tests", RFC 5231, January 2008.
 [Sieve]            Guenther, P., Ed. and T. Showalter, Ed., "Sieve:
                    An Email Filtering Language", RFC 5228,
                    January 2008.
 [URI]              Berners-Lee, T., Fielding, R., and L. Masinter,
                    "Uniform Resource Identifier (URI): Generic
                    Syntax", STD 66, RFC 3986, January 2005.
 [Variables]        Homme, K., "Sieve Extension: Variables", RFC 5229,
                    January 2008.

11.2. Informative References

 [ACAP]             Newman, C. and J. Myers, "ACAP -- Application
                    Configuration Access Protocol", RFC 2244,
                    November 1997.
 [IANA-GUIDELINES]  Narten, T. and H. Alvestrand, "Guidelines for
                    Writing an IANA Considerations Section in RFCs",
                    BCP 26, RFC 5226, May 2008.
 [TEL-URI]          Schulzrinne, H., "The tel URI for Telephone
                    Numbers", RFC 3966, December 2004.
 [XMPP]             Saint-Andre, Ed., P., "Extensible Messaging and
                    Presence Protocol (XMPP): Core", RFC 3920,
                    October 2004.

Melnikov, et al. Standards Track [Page 16] RFC 5435 Sieve Extension: Notifications January 2009

 [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.

Authors' Addresses

 Alexey Melnikov (editor)
 Isode Limited
 5 Castle Business Village
 36 Station Road
 Hampton, Middlesex  TW12 2BX
 UK
 EMail: Alexey.Melnikov@isode.com
 Barry Leiba (editor)
 IBM T.J. Watson Research Center
 19 Skyline Drive
 Hawthorne, NY  10532
 US
 Phone: +1 914 784 7941
 EMail: leiba@watson.ibm.com
 Wolfgang Segmuller
 IBM T.J. Watson Research Center
 19 Skyline Drive
 Hawthorne, NY  10532
 US
 Phone: +1 914 784 7408
 EMail: werewolf@us.ibm.com
 Tim Martin
 Endless Crossword
 672 Haight st.
 San Francisco, CA  94117
 US
 Phone: +1 510 260-4175
 EMail: timmartin@alumni.cmu.edu

Melnikov, et al. Standards Track [Page 17]

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