Sieve Extension: File Carbon Copy (Fcc)
draft-ietf-extra-sieve-fcc-05

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.

Status of This Memo

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Copyright Notice

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Table of Contents

• 1. Introduction
• 2. Conventions Used in This Document
• 3. Tagged Argument ":fcc"
• 3.1. Format of Filed Messages
• 3.2. Interaction with the Vacation Action
• 3.3. Interaction with the Notify Action
• 3.3.1. Notification-Capability "fcc"
• 3.4. Compatibility with Other Actions
• 3.5. Interaction with Fileinto Extensions
• 3.5.1. Imap4flags Extension
• 3.5.2. Mailbox Extension
• 3.5.3. Special-Use Extension
• 3.5.4. Extended Example
• 4. Implementation Status
• 5. Security Considerations
• 6. IANA Considerations
• 6.1. Registration of Sieve Extension
• 6.2. Registration of Notification-Capability Parameter
• 7. Acknowledgments
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Appendix A. Change History (To be removed by RFC Editor before publication)
• Authors' Addresses

1. Introduction

The Sieve Email Filtering Language 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 a new optional tagged argument ":fcc" to action commands which generate additional messages to allow a copy of the generated message to be filed into a target mailbox.

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

Each action that generates additional messages will need to specify how it interfacts with :fcc. This document also specifies the interaction of :fcc with the Vacation and Notify extensions.

2. Conventions Used in This Document

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

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"

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

FCC = ":fcc" <mailbox: string>

If the optional ":fcc" argument is specified with an action that generates an additional message, it instructs the Sieve interpreter to file a copy of the generated message into the target mailbox. The syntax and semantics of the mailbox argument MUST match those of the mailbox argument to the "fileinto" action specified in Section 4.1 of [RFC5228]. 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. Format of Filed Messages

Copies of messages filed into a mailbox via this extension are REQUIRED to be in Internet Message Format. 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 [RFC5322] and MIME ([RFC2045], [RFC2046], [RFC2047]).

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

• Date: The Date header field is REQUIRED and SHOULD be set to the date and time when the message was generated.
• 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.
• To: The To header field is OPTIONAL and MAY be set to the email address of the recipient of the generated message, if available.
• Subject: The Subject header field is OPTIONAL and MAY be generated as follows: The subject is set to the characters "Fcc: " followed by the subject of the message being processed by the Sieve interpreter.
• 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.
• 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.

3.2. Interaction with the Vacation Action

This document extends the "vacation" action (see also "vacation-seconds") 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:

require ["vacation", "fcc"];

vacation :days 7
         :from "hemingway@example.com" "Gone Fishin'"
         :fcc "INBOX.Sent";

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

3.3. Interaction with the Notify Action

This document extends the "notify" 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" notification method are MIME-compliant and MAY be filed into the target mailbox without modification.

Messages generated by other notification methods (e.g. "xmpp") MUST be encapsulated per Section 3.1 before being filed. The body of the filed message MUST include the :message parameter and MAY include one or more of the :from, :importance, or :options parameters. The MIME-type(s) of the body part(s) used to encapsulate the parameters is an implementation decision.

An implementation MAY only support :fcc in conjunction with a subset of the notification methods it supports. An error occurs if :fcc is combined with a notification method that doesn't support it. Notification methods that support :fcc can be discovered at run-time using the mechanism described below.

3.3.1. Notification-Capability "fcc"

This document defines a new notification-capability value "fcc" 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 can not 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";
}

3.4. 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 should describe their compatibility with ":fcc", and how to MIME-encapsulate the message, if required.

3.5. Interaction with Fileinto Extensions

The "fcc" extension can be used with some tagged arguments defined in extensions to the "fileinto" action. The sections below describe its interaction with currently defined extensions. Tagged arguments in future extensions to the "fileinto" command should describe their interaction with ":fcc", if any.

When any "fileinto" extension arguments are used with ":fcc", the corresponding extension MUST be enabled, and the arguments MUST have the same syntax and semantics as they do with "fileinto".

3.5.1. Imap4flags Extension

This document extends the definition of the ":flags" tagged argument so that it can optionally be used with the ":fcc" argument.

FCC =/ [":flags" <list-of-flags: string-list>]

If the optional ":flags" argument is specified with ":fcc", 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.

3.5.2. Mailbox Extension

This document extends the definition of the ":create" tagged argument so that it can optionally be used with the ":fcc" argument.

FCC =/ [":create"]

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

3.5.3. Special-Use Extension

This document extends the definition of the ":specialuse" tagged argument so that it can optionally be used with the ":fcc" argument.

FCC =/ [":specialuse" <special-use-flag: string>]

If the optional ":specialuse" argument is specified with ":fcc", 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 both the optional ":specialuse" and ":create" arguments are specified with ":fcc", the Sieve interpreter is instructed to create the target mailbox per Section 4.1 of [I-D.ietf-extra-sieve-special-use], if needed.

3.5.4. Extended Example

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

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

4. Implementation Status

< RFC Editor: before publication please remove this section and the reference to [RFC7942] >

This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC7942]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist.

According to [RFC7942], "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit".

4.1. Cyrus Server

The open source Cyrus Server project is a highly scalable enterprise mail system which supports Sieve email filtering at the point of final delivery. This production level Sieve implementation supports all of the requirements described in this document. This implementation is freely distributable under a BSD style license from Computing Services at Carnegie Mellon University.

4.2. Oracle Communications Messaging Server

The Oracle Communications Messaging Server is a highly scalable, reliable, and available messaging platform. This production level product supports the :fcc extension in conjunction with both the notify and vacation extensions. The implementation meets all the requirements given in this document. The product also supports the imap4flags extension so the :flags may be used in conjunction :fcc.

5. Security Considerations

The "fcc" extension does not raise any other security considerations that are not already present in [RFC5228], [RFC5230], [RFC5435], and [RFC6131].

6. IANA Considerations

6.1. Registration of Sieve Extension

• To: iana@iana.org
• Subject: Registration of new Sieve extension
• Capability name: fcc
• Description: Adds the ":fcc" parameter to Sieve action commands that generate additional messages.
• RFC number: RFC XXXX
• Contact address: The Sieve discussion list <sieve@ietf.org>

6.2. Registration of Notification-Capability Parameter

• To: iana@iana.org
• Subject: Registration of a new notification-capability parameter
• 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.
• Permanent and readily available reference(s): This RFC
• Contact information: The Sieve discussion list <ietf-mta-filters@imc.org>

7. Acknowledgments

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

8. References

8.1. Normative References

8.2. Informative References

Appendix A. Change History (To be removed by RFC Editor before publication)

Changes since draft-ietf-extra-sieve-fcc-03:

• Fixed typo in ABNF.

Changes since draft-ietf-extra-sieve-fcc-04:

• Editorial changes from Ned Freed.
• Added information on Oracle implementation.

Changes since draft-ietf-extra-sieve-fcc-02:

• Updated Keywords boilerplate.
• Noted that :fcc mailbox argument and any fileinto extension arguments used wth :fcc have the same syntax and semantics as they have with fileinto.
• Removed section on [e]Reject.
• Added "fcc" notification-capability.
• Added Implementation Status section.
• Editorial changes from Ned Freed.

Changes since draft-ietf-extra-sieve-fcc-01:

• Added text discussing how to handle generated messages that are not in MIME format.
• Adjusted ABNF so that tagged arguments that supplement :fcc no longer appear as positional.

Changes since draft-ietf-extra-sieve-fcc-00:

• Updated abstract with text from Ned.
• Added support for :fcc to notify extension.
• Prohibit use of :fcc with reject and ereject extensions.
• Added registration of the extension with IANA.
• Added Acknowledgments.
• Minor editorial changes.

Authors' Addresses