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Applications RFC Request for Comments SMTP ESMTP Sieve I-D Internet-Draft This document describes the "envelope-dsn" and "redirect-dsn" extensions to the Sieve email filtering language. The "envelope-dsn" extension provides access to additional envelope information provided by the delivery status notification extension to SMTP defined in RFC 3461. The "redirect-dsn" extension extends Sieve's redirect action to provide control over delivery status notification parameters. Fixed several typos. Changed name of extension from notary to envelope-dsn. Added the redirect-dsn extension. Updated references. Added a note about the use of ADDRESS-PART arguments with the new envelope-part strings defined by the envelope-dsn extension. Fleshed out the redirect-dsn extension. Changed document title to agree with new extension names. Added some examples. Fixed more typos. Changed dsn-envelope and dsn-redirect to envelope-dsn and redirect-dsn, respectively. Added a redirect-dsn example.

Sieve is a language for filtering email messages at or around the time of final delivery. It is designed to be implementable on either a mail client or mail server. It is suitable for running on a mail server where users may not be allowed to execute arbitrary programs, such as on black box Internet Message Access Protocol servers, as it has no user-controlled loops or the ability to run external programs. The base sieve specification defines the envelope extension and test to access information in the message envelope. Only information available in regular SMTP is provided; additional information added to the SMTP envelope by SMTP extensions cannot be accessed. The "envelope-dsn" extension extends the envelope test to allow access to the additional envelope fields defined by the SMTP extension for delivery status notification specified in RFC 3461. The base sieve specification also defines the redirect action which sends the message to a different address. Redirect only allows specification of the new recipient address. The "redirect-dsn" extension extends redirect to allow specification of some fields defined by the delivery status notification SMTP extension.

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 . The terms used to describe the various components of the Sieve language are taken from Section 1.1 of . This document uses the ABNF notation specified in and refers to the ABNF production notify-esmtp-value defined in Section 4.1 of .

The capability strings associated with the extensions defined in this document are "envelope-dsn" and "redirect-dsn".

The "envelope-dsn" extension does not define any new tests or actions, rather, it adds four values to the list of possible (case-insensitive) envelope-part strings defined in Section 5.4 of : Match the list of notification conditions, or NOTIFY values, associated with TO address used in the SMTP RCPT TO command that resulted in this message getting delivered to this user. More than one notification condition can be in effect at once; each condition that is in effect is tested separately and any match causes the text to succeed. The syntax and semantics of the NOTIFY parameter are defined in RFC 3461 section 4.1. Currently the possible notification condition values are "NEVER", "SUCCESS", "FAILURE" and "DELAY". Note that the value "NEVER" cannot be combined with any other value. Match the original recipient, or ORCPT, value in decoded form associated with the TO address used in the SMTP RCPT TO command that resulted in this message getting delivered to this user. The syntax and semantics of the ORCPT parameter are defined in Section 2.2 of RFC 3461. Match the return of content, or RET, value given in the SMTP MAIL FROM command. The syntax and semantics of the RET parameter are defined in RFC 3461 section 4.3. Currently the possible return of content values are "FULL" and "HDRS". Match the envelope identifier, or ENVID, value in decoded form given in the SMTP MAIL FROM command. The syntax and semantics of the ENVID parameter are defined in Section 4.4 of RFC 3461. All of these tests fail unconditionally if the specified envelope parameter does not exist for the current message or recipient. The envelope test's ADDRESS-PART argument assumes the string being tested has the syntax of an email address. None of the new envelope parts defined here have address syntax, accordingly, it is an error to specify an ADDRESS-PART argument in conjunction with these new envelope parts. The "relational" extension adds a match type called ":count". The count of an envelope test of with an envelope-part of "orcpt", "ret", and "envid" is 1 if the corresponding SMTP parameter is present and 0 otherwise. The count of an envelope test with an envelope-part of "notify" is equal to the number of notification conditions specified and 0 if the NOTIFY parameter is not present.

The fact that the notify envelope-part operates on a list of values makes it easy to check to see if a given value is present without having to worry about other values:

Checking to see if a given request is the only one present is a little trickier, however:

The orcpt envelope-part contains an address type indicator in addition to an address, which must be taken into account:

The "redirect-dsn" extension does not define any new tests or actions, rather, it adds two new arguments, NOTIFY and RET, to the redirect action defined in Section 4.2 of . This updates the usage description for redirect to:

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The syntax for the NOTIFY and RET arguments are:

The notify-esmtp-value production is defined in Section 4.1 of . When these arguments are specified, they set the corresponding NOTIFY ESMTP RCPT TO and RET ESMTP MAIL FROM parameters, respectively. These parameters are only available when the delivery status notification (DSN) ESMTP extension is available; they are simply ignored and MUST NOT cause an error if the DSN extension is unavailable.

One possible use of :notify on redirect is to ccmbine the copy extension with the ability to suppress nondelivery notifications to generate a private copy of selected messages with no side effects or error notifications:

The envelope-dsn extension provides access to additional message envelope information. This is not believed to raise any additional security issues beyond those for the Sieve "envelope" test. The redirect-dsn extension allows specification of the delivery status notification's NOTIFY parameter which can cause the generation of notification messages that might otherwise not be generated, especially if notification in the event of successful delivery is required. Sites which limit the ability to request success notifications will also need to restrict the ability to request them using the redirect-dsn extension. All of the security considerations given in the base Sieve specification also apply to this extension.

The following template specifies the IANA registration of the Sieve extension specified in this document: To: iana@iana.org Subject: Registration of new Sieve extensions Capability name: envelope-dsn Description: The "envelope-dsn" extension extends the envelope test to allow checking of information associated with the DSN ESMTP extension defined in RFC 3461. RFC number: RFC &rfc.number; Contact address: Sieve discussion list <ietf-mta-filters@imc.org> Capability name: redirect-dsn Description: The "redirect-dsn" extension extends the redirect action to allow specification of the NOTIFY and RET ESMTP parameters associated with the DSN SMTP extension defined in RFC 3461. RFC number: RFC &rfc.number; Contact address: Sieve discussion list <ietf-mta-filters@imc.org> This information should be added to the list of sieve extensions given on http://www.iana.org/assignments/sieve-extensions.

Cyrus Daboo, Derek Diget, Philip Guenther, Arnt Gulbrandsen, Alexey Melnikov, and Alexandros Vellis provided helpful suggestions and corrections.