Internet Engineering Task Force (IETF) K. Murchison

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.

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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.

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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.

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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.

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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

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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 "[email protected]" "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.

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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:[email protected]";

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:

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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:[email protected]?message;subject=SIEVE";
} else {
notify :fcc "INBOX.Sent"
:message "You got mail!"
"mailto:[email protected]";
}

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.

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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 <[email protected]>

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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 <[email protected]>

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>.

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[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>.

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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: [email protected]

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

Email: [email protected]

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