Sieve Email Filtering:
Delivery Status Notifications Extension
Sun Microsystems800 Royal OaksMonroviaCA91016-6347USA+1 909 457 4293ned.freed@mrochek.com
Applications
RFCRequest for CommentsSMTPESMTPSieveI-DInternet-Draft
This document describes the "dsn-envelope" and "dsn-redirect" extensions to the
Sieve email filtering language. The "dsn-envelope" extension provides access to
additional envelope information provided by the delivery status notification
extension to SMTP defined in RFC 3461. The "dsn-redirect" extension extends
Sieve's redirect action to provide control over delivery status notification
parameters.
Fixed several typos.
Changed name of extension from notary to dsn-envelope.
Added the dsn-redirect extension.
Updated references.
Added a note about the use of ADDRESS-PART arguments with the new envelope-part
strings defined by the dsn-envelope extension.
Fleshed out the dsn-redirect extension.
Changed document title to agree with new extension names.
Added some examples.
Fixed more typos.
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 "dsn-envelope" 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 "dsn-redirect" 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 "dsn-envelope" and "dsn-redirect".
The "dsn-envelope" 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 havingt 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 "dsn-redirect" 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:
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.
The dsn-envelope 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 dsn-redirect 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 dsn-redirect extension.
All of the security considerations given in the base Sieve
specification also apply to this extension.
Cyrus Daboo, Derek Diget, Philip Guenther, Arnt Gulbrandsen, Alexey Melnikov, and
Alexandros Vellis provided
helpful suggestions and corrections.