Network Working Group N. Freed
Internet-Draft Oracle
Intended status: Standards Track March 24, 2010
Expires: September 25, 2010
Sieve Email Filtering: Delivery Status Notifications and Deliver-By
Extensions
draft-freed-sieve-notary-07
Abstract
This document describes the "envelope-dsn", "redirect-dsn",
"envelope-deliverby", and "redirect-deliverby" extensions to the
Sieve email filtering language. The "envelope-dsn" and "envelope-
deliverby" extensions provide access to additional envelope
information provided by the delivery status notification and
deliver-by SMTP extensions. The "redirect-dsn" and "redirect-
deliverby" extensions extend Sieve's redirect action to provide
control over delivery status notification and deliver-by parameters,
respectively.
Change History (to be removed prior to publication as an RFC
Clarified orcpt decoding.
Changed the ABNF for notary values to disallow spaces.
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-
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dsn, respectively.
Added a redirect-dsn example.
Added the two deliver-by extensions.
Status of this Memo
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1. Introduction
Sieve [RFC5228] is a language for filtering email messages at or
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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 [RFC3501] 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 [RFC5321] 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
[RFC3461]. The "envelope-deliverby" extension extends the envelope
test to allow access to the additional envelope fields defined by the
deliver-by SMTP extension defined in [RFC2852].
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.
"redirect-deliverby" in turn provides the ability to set a time limit
for delivery as specified in RFC 2852 [RFC2852].
2. Conventions used in this document
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 [RFC2119].
The terms used to describe the various components of the Sieve
language are taken from Section 1.1 of [RFC5228].
This document uses the ABNF notation specified in [RFC5234], and
refers to the ABNF productions notify-esmtp-value defined in Section
4.1 of [RFC3461].
3. Capability Identifier
The capability strings associated with the extensions defined in this
document are "envelope-dsn", "redirect-dsn", "envelope-deliverby",
and "redirect-deliverby".
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4. Envelope-dsn Extension
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
[RFC5228]:
notify - Match the list of notification conditions, or NOTIFY
values, associated with the 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 test to succeed. The syntax and semantics of
the NOTIFY parameter are defined in Section 4.1 of RFC 3461
[RFC3461] . Currently the possible notification condition values
are "NEVER", "SUCCESS", "FAILURE" and "DELAY". Note that the
value "NEVER" cannot be combined with any other value.
orcpt - Match the original recipient, or ORCPT, value associated
with the TO address used in the SMTP RCPT TO command that resulted
in this message getting delivered to this user, with xtext
encoding removed. The syntax and semantics of the ORCPT parameter
are defined in Section 4.2 of RFC 3461 [RFC3461].
ret - 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 Section 4.3 of RFC 3461 [RFC3461]. Currently the
possible return of content values are "FULL" and "HDRS".
envid - 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 [RFC3461].
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 [RFC5231] adds a match type called
":count". The count of an envelope test 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
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conditions specified and 0 if the NOTIFY parameter is not present.
4.1. Examples
The fact that the NOTIFY envelope parameter is multivalued and the
notify envelope-part turns this into a list of values makes it easy
to check to see if a given value is present without having to worry
about other values:
require ["envelope", "envelope-dsn"];
# Check whether SUCCESS notifications were requested,
# irrespective of any other requests that were made
if envelope "notify" "SUCCESS"
{
# do whatever
}
Checking to see if a given request is the only one present is a
little trickier, however:
require ["envelope", "envelope-dsn", "relational",
"comparator-i;ascii-numeric"];
# Check whether only FAILURE notifications were requested
if allof ( envelope "notify" "FAILURE",
envelope :comparator "i;ascii-numeric"
:count "eq" "notify" "1"
)
{
# do whatever
}
The orcpt envelope-part always contains an address type indicator
prefix in addition to an address, which must be taken into account in
any tests:
require ["envelope", "envelope-dsn"];
# See if the orcpt is an RFC822 address in the example.com
# domain
if envelope :matches "orcpt" "rfc822;*@example.com"
{
# do whatever
}
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5. Envelope-deliverby Extension
The "envelope-deliverby" extension does not define any new tests or
actions, rather, it adds three values to the list of possible (case-
insensitive) envelope-part strings defined in Section 5.4 of
[RFC5228]. These new envelope parts are defined in Section 5 of
[RFC2852].
bytime - Match the initial integer part of the deliver-by
extension's BY parameter specified in the SMTP MAIL FROM command.
bymode - Match a string computed from the by-mode part of the
deliver-by extension's BY parameter. The possible values are
"notify" and "return", which correspond to the BY parameter mode
specifier characters "N" and "R" respectively.
bytrace - Match the trace modifier computed from the by-trace
modifier on the deliver-by extension's BY parameter. The possible
values are "trace" and "" (the empty string). These values
correspond to the presence or absence of the by-trace "T" modifier
respectively.
All of these tests fail unconditionally if the BY SMTP MAIL FROM
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 [RFC5231] adds a match type called
":count". The count of an envelope test with an envelope-part of
"bytime", "bymode", and "bytrace" is 1 if the BY parameter is present
and 0 otherwise.
It should be noted that the deliver-by by-time is decremented as the
message passes through the transport infrastructure. Accordingly, it
is not possible to tell what the message originator set the value to,
only the amount of time remaining at the moment the sieve is run.
5.1. Example
As noted above, this extension does not provide access to the
originator's initial by-time setting for the simple reason that this
information is not part of the envelope. It can, however, be used to
check and see if the message was delivered within the alloted time.
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require ["envelope", "envelope-deliverby", "relational",
"comparator-i;ascii-numeric"];
# Check to see if this message didn't make it in the time alloted by
# the originator.
if envelope :value "eq" :comparator "i;ascii-numeric" "bytime" "0"
{
# do whatever
}
6. redirect-dsn extension
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 [RFC5228]. This updates
the usage description for redirect to:
[
Usage: redirect [:notify "value"] [:ret "FULL"|"HDRS"]
<address: string>
The syntax for the NOTIFY and RET arguments are:
NOTIFY = ":notify" notify-value
notify-value = DQUOTE ("NEVER" / notify-esmtp-list) DQUOTE
notify-esmtp-list = notify-list-element *("," notify-list-element)
RET = ":ret" ret-value
ret-value = DQUOTE ("FULL" / "HDRS") DQUOTE
The notify-list-element production is defined in Section 4.1 of
[RFC3461].
When these arguments are specified, they set the corresponding NOTIFY
ESMTP RCPT TO and RET ESMTP MAIL FROM parameters, respectively.
These arguments are only honored if the delivery status notification
(DSN) ESMTP extension is available. When the DSN extension is not
available, these arguments MUST be ignored and MUST NOT cause an
error.
6.1. Example
One possible use of :notify on redirect is to combine the copy
extension [RFC3894] with the ability to suppress nondelivery
notifications to generate a private copy of selected messages with no
side effects or error notifications:
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require ["copy", "redirect-dsn"];
# Make a private copy of messages from user@example.com
if address "from" "user@example.com"
{
redirect :copy :notify "NEVER" "elsewhere@example.com";
}
7. redirect-deliverby extension
The "redirect-deliverby" extension does not define any new tests or
actions, rather, it adds three new arguments, BYTIME, BYMODE, and
BYTRACE, to the redirect action defined in Section 4.2 of [RFC5228].
This updates the usage description for redirect to:
[
Usage: redirect [:bytime <limit: number>
[:bymode "notify"|"return"] [:bytrace]]
<address: string>
:bytime specifies the number of seconds within which the message
should be delivered. :bymode specifies whether a notification should
be sent or the message simply returned if the time limit is exceeded.
The default is "return" if :bymode is not specified. See The
semantics of delivery time limits are specified and discussed at
length in [RFC2852].
It is an error to specify :bymode and :bytrace without :bytime.
When these arguments are specified, they are used to construct the
corresponding BY ESMTP MAIL FROM parameter. The :bytime value
becomes the by-time, the :bymode becomes the by-mode value, and
:bytrace sets the by-trace modifier. If the deliver-by extension is
unavailable, the handling of reredirected message MUST conform to the
semantics specified in [RFC2852] section 4.1.4 for relaying to a
server that does not support the deliver-by SMTP extension.
7.1. Example
The obvious use of "redirect-deliverby" is to specify a limit on
delivery attempts for a redirected message:
require ["copy", "redirect-deliverby"];
# Send a copy to my cell phone, time out after 10 minutes
if address "from" "user@example.com"
{
redirect :copy :bytime 600 "cellphone@example.com";
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}
8. Security Considerations
The envelope-dsn and envelope-deliverby extensions provide 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.
Similarly, the redirect-deliverby extension is used to control how
long the transport infrastructure will continue to attempt to deliver
a message before giving up, which could result in the generation of
additional notification messages. While the underlying Deliver-By
extension does have a minimum by-time limit, sites may wish to impose
additional limits on the minimum by-time allowed in a redirect
action.
All of the security considerations given in the base Sieve
specification also apply to this extension.
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9. IANA Considerations
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 XXXX
Contact address: Sieve discussion list <sieve@ietf.org>
Capability name: envelope-deliverby
Description: The "envelope-deliverby" extension extends the
envelope test to allow checking of information
associated with the Deliver-By ESMTP extension
defined in RFC 2852.
RFC number: RFC XXXX
Contact address: Sieve discussion list <sieve@ietf.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 XXXX
Contact address: Sieve discussion list <sieve@ietf.org>
Capability name: redirect-deliverby
Description: The "redirect-deliverby" extension extends the
redirect action to allow specification of the BY
ESMTP parameter associated with the Deliver-By SMTP
extension defined in RFC 2852.
RFC number: RFC XXXX
Contact address: Sieve discussion list <sieve@ietf.org>
This information should be added to the list of sieve extensions
given on http://www.iana.org/assignments/sieve-extensions.
10. References
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10.1. Normative references
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2852] Newman, D., "Deliver By SMTP Service Extension", RFC 2852,
June 2000.
[RFC3461] Moore, K., "Simple Mail Transfer Protocol (SMTP) Service
Extension for Delivery Status Notifications (DSNs)",
RFC 3461, January 2003.
[RFC5228] Guenther, P. and T. Showalter, "Sieve: An Email Filtering
Language", RFC 5228, January 2008.
[RFC5231] Segmuller, W. and B. Leiba, "Sieve Email Filtering:
Relational Extension", RFC 5231, January 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008.
10.2. Informative references
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
[RFC3894] Degener, J., "Sieve Extension: Copying Without Side
Effects", RFC 3894, October 2004.
Appendix A. Acknowledgements
Cyrus Daboo, Derek Diget, Philip Guenther, Arnt Gulbrandsen, Barry
Leiba, Andrew McKeon, Alexey Melnikov, Chris Newman, Aaron Stone, and
Alexandros Vellis provided helpful suggestions and corrections.
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Author's Address
Ned Freed
Oracle
800 Royal Oaks
Monrovia, CA 91016-6347
USA
Phone: +1 909 457 4293
Email: ned.freed@mrochek.com
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