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RFC 8580 - Sieve Extension: File Carbon Copy (FCC)


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Internet Engineering Task Force (IETF)                      K. Murchison
Request for Comments: 8580                                   B. Gondwana
Updates: 5230, 5435                                             FastMail
Category: Standards Track                                       May 2019
ISSN: 2070-1721

                Sieve Extension: File Carbon Copy (FCC)

Abstract

   The Sieve email filtering language provides a number of action
   commands, some of which can generate additional messages on behalf of
   the user.  This document defines an extension to such commands to
   allow a copy of any generated message to be filed into a target
   mailbox.

   This document updates RFCs 5230 and 5435 by adding a new tagged
   argument to the Vacation and Notify actions, respectively.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8580.

Copyright Notice

   Copyright (c) 2019 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   3.  Tagged Argument ":fcc"  . . . . . . . . . . . . . . . . . . .   3
     3.1.  Interaction with Extensions to the Fileinto Action  . . .   3
       3.1.1.  Imap4flags Extension  . . . . . . . . . . . . . . . .   4
       3.1.2.  Mailbox Extension . . . . . . . . . . . . . . . . . .   4
       3.1.3.  Special-Use Extension . . . . . . . . . . . . . . . .   4
     3.2.  Collected Grammar . . . . . . . . . . . . . . . . . . . .   5
   4.  Format of FCC Messages  . . . . . . . . . . . . . . . . . . .   5
   5.  Interaction with the Vacation Action  . . . . . . . . . . . .   6
   6.  Interaction with the Notify Action  . . . . . . . . . . . . .   7
     6.1.  Notification-Capability "fcc" . . . . . . . . . . . . . .   7
   7.  Compatibility with the Reject and Extended Reject
       Actions . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Compatibility with Other Actions  . . . . . . . . . . . . . .   8
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   10. Privacy Considerations  . . . . . . . . . . . . . . . . . . .   9
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  Registration of New Sieve Extension  . . . . . . . . . .   9
     11.2.  Registration of New Notification-Capability
            Parameter  . . . . . . . . . . . . . . . . . . . . . . .  10
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     12.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The Sieve email filtering language [RFC5228] provides a number of
   action commands, some of which can generate additional messages on
   behalf of the user.  It is sometimes desirable for a Sieve user to
   maintain an archive of the messages generated by these commands.

   This extension defines ":fcc", a new optional tagged argument for
   action commands that generate additional messages.  This argument
   allows a copy of the generated message to be filed into a target
   mailbox.

   The capability string associated with this extension is "fcc".

   Each new action that generates additional messages will need to
   specify how it interacts with the FCC extension.  This document
   specifies the interaction of the FCC extension with the Vacation
   [RFC5230] and Notify [RFC5435] actions.

2.  Conventions Used in This Document

   Conventions for notations are as described in Section 1.1 of
   [RFC5228], including use of the "Usage:" label for the definition of
   the action and the syntax of tagged arguments.

   The 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
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Tagged Argument ":fcc"

   This document specifies ":fcc", a new optional tagged argument that
   alters the behavior of action commands that generate additional
   messages on behalf of the user.

   Usage: :fcc <mailbox: string>

   The ":fcc" tagged argument instructs the Sieve interpreter to file a
   copy of the generated message into the mailbox provided in the
   subsequent argument.  The semantics and treatment of the mailbox
   argument are defined to match those of the mailbox argument to the
   fileinto action specified in Section 4.1 of [RFC5228].  Specifically,
   use of an invalid mailbox name MAY be treated as an error or result
   in delivery to an implementation-defined mailbox, and if the
   specified mailbox doesn't exist, the implementation MAY treat it as
   an error, create the mailbox, or file the message into an
   implementation-defined mailbox.

3.1.  Interaction with Extensions to the Fileinto Action

   Some tagged arguments defined in extensions to the fileinto action
   can be used together with the ":fcc" tagged argument.  The sections
   below describe these interactions.  Tagged arguments in future
   extensions to the fileinto action need to describe their interaction
   with the FCC extension, if any.

   When any fileinto extension arguments are used with the FCC
   extension, the corresponding extension MUST be enabled, and the
   arguments are defined to have the same syntax, semantics, and
   treatment as they do with the fileinto action.

3.1.1.  Imap4flags Extension

   This document extends the definition of the ":flags" tagged argument
   (see Section 5 of [RFC5232]) so that it can optionally be used with
   the ":fcc" tagged argument.

   Usage: :fcc <mailbox: string> [:flags <list-of-flags: string-list>]

   If the optional ":flags" tagged argument is specified with the ":fcc"
   tagged argument, it instructs the Sieve interpreter to set the IMAP4
   flags provided in the subsequent argument when the generated message
   is filed into the target mailbox.

3.1.2.  Mailbox Extension

   This document extends the definition of the ":create" tagged argument
   (see Section 3.2 of [RFC5490]) so that it can optionally be used with
   the ":fcc" tagged argument.

   Usage: :fcc <mailbox: string> [:create]

   If the optional ":create" tagged argument is specified with the
   ":fcc" tagged argument, it instructs the Sieve interpreter to create
   the target mailbox, if needed, before attempting to file the
   generated message into the target mailbox.

3.1.3.  Special-Use Extension

   This document extends the definition of the ":specialuse" tagged
   argument (see Section 4 of [RFC8579]) so that it can optionally be
   used with the ":fcc" tagged argument.

  Usage: :fcc <mailbox: string> [:specialuse <special-use-flag: string>]

   If the optional ":specialuse" tagged argument is specified with the
   ":fcc" tagged argument, it instructs the Sieve interpreter to check
   whether a mailbox exists with the specific special-use flag assigned
   to it.  If such a mailbox exists, the generated message is filed into
   the special-use mailbox.  Otherwise, the generated message is filed
   into the target mailbox.

   If the optional ":specialuse" and ":create" tagged arguments are both
   specified with the ":fcc" tagged argument, the Sieve interpreter is
   instructed to create the target mailbox per Section 4.1 of [RFC8579],
   if needed.

3.2.  Collected Grammar

   For convenience, the "FCC" syntax element is defined here using ABNF
   [RFC5234] so that it can be augmented by other extensions.

   Note that the following is the grammar of "FCC" after it has been
   lexically interpreted.  No whitespace or comments appear below.

   FCC         = ":fcc" string *FCC-OPTS
                   ; per Section 2.6.2 of RFC 5228,
                   ; the tagged arguments in FCC may appear in any order

   FCC-OPTS    = CREATE / IMAP-FLAGS / SPECIAL-USE
                   ; each option MUST NOT appear more than once

   CREATE      = ":create"
   IMAP-FLAGS  = ":flags" string-list
   SPECIAL-USE = ":specialuse" string

4.  Format of FCC Messages

   Copies of messages filed into a mailbox via this extension are
   REQUIRED to be in the Internet Message Format [RFC5322].  Some
   messages generated by Sieve actions might already conform to this
   format and MAY be filed without modification.  Messages generated in
   other formats MUST be encapsulated using constructs from the Internet
   Message Format [RFC5322] and MIME ([RFC2045], [RFC2046], [RFC2047],
   [RFC2231]).

   The general requirements for encapsulating the copies of messages to
   be filed are as follows:

   o  Date: The Date header field is REQUIRED and SHOULD be set to the
      date and time when the message was generated.

   o  From: The From header field is REQUIRED and SHOULD be set to the
      email address of the owner of the Sieve script, unless explicitly
      overridden by rules for encapsulating a particular message type.

         Per Erratum ID 2035 [Err2035],

         "Informative advice: Users often have multiple email addresses,
         and "the email address of the owner of the Sieve script" may
         offer a choice among several.  If the sieve processor
         recognizes an address belonging to the owner of the Sieve
         script in the To or Cc fields of the input message, then it's

         better to use that address for the From field of the generated
         message, rather than any other addresses the script's owner may
         also have".

   o  To: The To header field is OPTIONAL and MAY be set to the email
      address of the recipient of the generated message, if available.

   o  Subject: The Subject header field is OPTIONAL and MAY be generated
      by setting the subject to the characters "Fcc: " followed by the
      subject of the message being processed by the Sieve interpreter.

   o  In-Reply-To: The In-Reply-To header field is OPTIONAL and MAY be
      set to the Message-ID of the message being processed by the Sieve
      interpreter.

   o  Message Body: The body of the filed message is REQUIRED and is
      composed of one or more MIME parts containing the generated
      message and any related metadata.  The Content-Type header
      field(s) MUST be set to the appropriate MIME types.  If any of the
      MIME parts include 8-bit or binary data, the Content-Transfer-
      Encoding header field(s) MUST be set accordingly.

5.  Interaction with the Vacation Action

   This document extends the Vacation [RFC5230] action (see also
   "Seconds" parameter [RFC6131] to optionally store a copy of the auto-
   reply messages into a target mailbox.

   Usage:   vacation [FCC]
                     [":days" number | ":seconds" number]
                     [":subject" string]
                     [":from" string]
                     [":addresses" string-list]
                     [":mime"]
                     [":handle" string]
                     <reason: string>

   Example (using fileinto extensions):

   require ["vacation", "fcc", "mailbox", "special-use", "imap4flags"];

   vacation :days 7
            :from "hemingway@example.com" "Gone Fishin'"
            :specialuse "\\Sent" :create
            :fcc "INBOX.Sent" :flags ["\\Seen"];

   Vacation auto-reply messages are compliant with MIME and can be filed
   into the target mailbox without modification.

6.  Interaction with the Notify Action

   This document extends the Notify [RFC5435] action to optionally store
   a copy of the notification messages into a target mailbox.

   Usage:   notify [FCC]
                   [":from" string]
                   [":importance" <"1" / "2" / "3">]
                   [":options" string-list]
                   [":message" string]
                   <method: string>

   Example:

   require ["enotify", "fcc"];

   notify :fcc "INBOX.Sent"
          :message "You got mail!"
          "mailto:ken@example.com";

   Messages generated using the "mailto" [RFC5436] notification method
   are compliant with MIME and can be filed into the target mailbox
   without modification.

   Messages generated by other notification methods (e.g., "xmpp"
   [RFC5437]) MUST be encapsulated per Section 4 before being filed.
   The body of the filed message MUST include the ":message" tagged
   argument and MAY include one or more of the ":from", ":importance",
   or ":options" tagged arguments.  The MIME type(s) of the body part(s)
   used to encapsulate the parameters is an implementation decision.

   An implementation MAY only support the FCC extension in conjunction
   with a subset of the notification methods it supports.  An error
   occurs if the FCC extension is used with a notification method that
   doesn't support it.  Notification methods that support the FCC
   extension can be discovered at runtime using the mechanism described
   in Section 6.1.

6.1.  Notification-Capability "fcc"

   This document defines "fcc", a new notification-capability value for
   use with the notify_method_capability test (see Section 5 of
   [RFC5435].  For the "fcc" notification-capability, the
   notify_method_capability test can match one of the following key-list
   values:

   yes
      A copy of the notification message sent using the method
      identified by the notification-uri can be filed into a target
      mailbox.

   no
      A copy of the notification message sent using the method
      identified by the notification-uri cannot be filed into a target
      mailbox.

   Note that the "fcc" notify_method_capability test does not require
   the notification-uri argument to specify anything other than a
   scheme.

   Example:

   require ["enotify", "fcc"];

   if notify_method_capability "xmpp:" "fcc" "yes" {
       notify :fcc "INBOX.Sent"
              :message "You got mail"
              "xmpp:ken@example.com?message;subject=SIEVE";
   } else {
       notify :fcc "INBOX.Sent"
              :message "You got mail!"
              "mailto:ken@example.com";
   }

7.  Compatibility with the Reject and Extended Reject Actions

   Implementations MUST NOT allow use of the FCC extension with the
   reject and ereject [RFC5429] actions.  Allowing use of the FCC
   extension with these actions would violate the SMTP [RFC5321]
   principle that a message is either delivered or bounced back to the
   sender.  Namely, the saved copy of the rejection message will contain
   the original message.

   It is an error for a script to use the ":fcc" tagged argument with
   either of the reject or ereject actions.

8.  Compatibility with Other Actions

   The FCC extension is not compatible with any Sieve action that does
   not generate an additional message on behalf of the user.  It is an
   error for a script to use the ":fcc" tagged argument with any such
   action.

   Future extensions that define actions that generate additional
   messages on behalf of the user need to describe their compatibility
   with the FCC extension and describe how to MIME-encapsulate the
   message, if required.

9.  Security Considerations

   In addition to the security considerations in [RFC5228], [RFC5230],
   [RFC5435], and [RFC6131], it should be noted that filing copies of
   generated messages may cause the Sieve script owner to exceed the
   allocated storage (quota) on the mail system, thereby preventing
   delivery of future messages destined for the owner.

10.  Privacy Considerations

   In addition to the privacy considerations in [RFC5228], [RFC5230],
   [RFC5435], and [RFC6131], it should be noted that a copy of a
   generated message filed into a shared or public mailbox (as opposed
   to a private mailbox) could expose private information about the
   Sieve script owner to third parties.  For instance, users that have
   access to the shared/public mailbox might discover that the Sieve
   script owner is on holiday or might discover the owner's physical
   location.

11.  IANA Considerations

11.1.  Registration of New Sieve Extension

   IANA has registered the following Sieve extension in the "Sieve
   Extensions" registry at
   <https://www.iana.org/assignments/sieve-extensions>:

      Capability name: fcc

      Description: Adds the ":fcc" parameter to Sieve action commands
      that generate additional messages.

      RFC number: RFC 8580

      Contact address: The Sieve discussion list <sieve@ietf.org>

11.2.  Registration of New Notification-Capability Parameter

   IANA has registered the following notification-capability parameter
   in the "Notification-Capability Parameters" registry at
   <https://www.iana.org/assignments/notification-capability-
   parameters>:

      Capability Name: fcc

      Description: Returns whether a copy of the notification message
      sent using the method identified by the notification-uri parameter
      to the notify_method_capability test can be filed into a target
      mailbox.

      Syntax: Can contain one of two values: "yes" or "no".  Values MUST
      be in lowercase.

      Reference: RFC 8580

      Contact: The Sieve discussion list <sieve@ietf.org>

12.  References

12.1.  Normative References

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
              <https://www.rfc-editor.org/info/rfc2045>.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              DOI 10.17487/RFC2046, November 1996,
              <https://www.rfc-editor.org/info/rfc2046>.

   [RFC2047]  Moore, K., "MIME (Multipurpose Internet Mail Extensions)
              Part Three: Message Header Extensions for Non-ASCII Text",
              RFC 2047, DOI 10.17487/RFC2047, November 1996,
              <https://www.rfc-editor.org/info/rfc2047>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2231]  Freed, N. and K. Moore, "MIME Parameter Value and Encoded
              Word Extensions: Character Sets, Languages, and
              Continuations", RFC 2231, DOI 10.17487/RFC2231, November
              1997, <https://www.rfc-editor.org/info/rfc2231>.

   [RFC5228]  Guenther, P., Ed. and T. Showalter, Ed., "Sieve: An Email
              Filtering Language", RFC 5228, DOI 10.17487/RFC5228,
              January 2008, <https://www.rfc-editor.org/info/rfc5228>.

   [RFC5230]  Showalter, T. and N. Freed, Ed., "Sieve Email Filtering:
              Vacation Extension", RFC 5230, DOI 10.17487/RFC5230,
              January 2008, <https://www.rfc-editor.org/info/rfc5230>.

   [RFC5232]  Melnikov, A., "Sieve Email Filtering: Imap4flags
              Extension", RFC 5232, DOI 10.17487/RFC5232, January 2008,
              <https://www.rfc-editor.org/info/rfc5232>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              DOI 10.17487/RFC5322, October 2008,
              <https://www.rfc-editor.org/info/rfc5322>.

   [RFC5429]  Stone, A., Ed., "Sieve Email Filtering: Reject and
              Extended Reject Extensions", RFC 5429,
              DOI 10.17487/RFC5429, March 2009,
              <https://www.rfc-editor.org/info/rfc5429>.

   [RFC5435]  Melnikov, A., Ed., Leiba, B., Ed., Segmuller, W., and T.
              Martin, "Sieve Email Filtering: Extension for
              Notifications", RFC 5435, DOI 10.17487/RFC5435, January
              2009, <https://www.rfc-editor.org/info/rfc5435>.

   [RFC5490]  Melnikov, A., "The Sieve Mail-Filtering Language --
              Extensions for Checking Mailbox Status and Accessing
              Mailbox Metadata", RFC 5490, DOI 10.17487/RFC5490, March
              2009, <https://www.rfc-editor.org/info/rfc5490>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8579]  Bosch, S., "Sieve Email Filtering: Delivering to Special-
              Use Mailboxes", RFC 8579, DOI 10.17487/RFC8579, May 2019,
              <https://www.rfc-editor.org/info/rfc8579>.

12.2.  Informative References

   [Err2035]  RFC Errata, Errata ID 2035, RFC 5230,
              <https://www.rfc-editor.org/errata_search.php?eid=2035>.

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              DOI 10.17487/RFC5321, October 2008,
              <https://www.rfc-editor.org/info/rfc5321>.

   [RFC5436]  Leiba, B. and M. Haardt, "Sieve Notification Mechanism:
              mailto", RFC 5436, DOI 10.17487/RFC5436, January 2009,
              <https://www.rfc-editor.org/info/rfc5436>.

   [RFC5437]  Saint-Andre, P. and A. Melnikov, "Sieve Notification
              Mechanism: Extensible Messaging and Presence Protocol
              (XMPP)", RFC 5437, DOI 10.17487/RFC5437, January 2009,
              <https://www.rfc-editor.org/info/rfc5437>.

   [RFC6131]  George, R. and B. Leiba, "Sieve Vacation Extension:
              "Seconds" Parameter", RFC 6131, DOI 10.17487/RFC6131, July
              2011, <https://www.rfc-editor.org/info/rfc6131>.

Acknowledgments

   The authors would like to thank the following individuals for
   contributing their ideas and supporting this specification: Ned
   Freed, Stan Kalisch, and Alexey Melnikov.

Authors' Addresses

   Kenneth Murchison
   FastMail US LLC
   1429 Walnut Street, Suite 1201
   Philadelphia, PA  19102
   United States of America

   Email: murch@fastmailteam.com

   Bron Gondwana
   FastMail Pty Ltd
   Level 2, 114 William Street
   Melbourne, VIC  3000
   Australia

   Email: brong@fastmailteam.com

 

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