    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.

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    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

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    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].

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       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

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       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.

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    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}";
               }

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               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

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       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

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       (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.

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       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.

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       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.

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       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.

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       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/.

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    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

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       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]