RFC6009

Internet Engineering Task Force (IETF) N. Freed Request for Comments: 6009 Oracle Category: Standards Track October 2010 ISSN: 2070-1721

                     Sieve Email Filtering:
    Delivery Status Notifications and Deliver-By Extensions

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 (DSN) and Deliver-By SMTP extensions, respectively. The "redirect-dsn" and "redirect-deliverby" extensions extend Sieve's redirect action to provide control over delivery status notification and Deliver-By parameters, 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 5741.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6009.

Copyright Notice

Copyright (c) 2010 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 (http://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.

Introduction

Sieve RFC5228 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 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 notifications (DSNs) 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.

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. The nature and handling of Sieve errors are described in Section 2.10.6 of RFC5228.

This document uses the ABNF notation specified in RFC5234, and refers to the notify-esmtp-value ABNF production defined in Section 4.1 of RFC3461.

Capability Identifiers

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

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" is never 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.  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.

The envelope test fails unconditionally for each of these envelope- part strings 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 conditions specified and 0 if the NOTIFY parameter is not present.

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"];

1. Check whether SUCCESS notifications were requested,
2. 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"];

1. 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"];

1. See if the orcpt is an RFC822 address in the example.com
2. domain

if envelope :matches "orcpt" "rfc822;*@example.com" {

   # do whatever

}

Envelope-deliverby Extension

The "envelope-deliverby" 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 and an optional :zone tagged argument. This updates the usage description for envelope to:

Usage: envelope [COMPARATOR] [ADDRESS-PART]

                 [MATCH-TYPE] [:zone <time-zone: string>]
                 <envelope-part: string-list>
                 <key-list: string-list>

These new envelope parts correspond to the new MAIL FROM parameters defined in Section 4 of RFC2852. They are:

bytimeabsolute - Match the current value of the initial integer part

  of the Deliver-By extension's BY parameter on the SMTP MAIL FROM
  command, converted into an absolute time represented in restricted
  ISO 8601 format.  The restricted ISO 8601 format is specified by
  the date-time ABNF production given in RFC3339, Section 5.6,
  with the added restrictions that the letters "T" and "Z" MUST be
  in upper case, and a time zone offset of zero MUST be represented
  by "Z" and not "+00:00".

bytimerelative - Match the current value of 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.

The envelope test fails unconditionally for each of these envelope- part strings if the BY SMTP MAIL FROM parameter does not exist for the current message or recipient.

The new :zone argument specifies a time zone offset string that any bytimeabsolute value is to be shifted to prior to testing. :zone has no effect on envelope-parts other than bytimeabsolute. The value of the time zone offset string MUST be an offset relative to UTC with the following syntax:

time-zone = ( "+" / "-" ) 4DIGIT

The "+" or "-" indicates whether the time-of-day is ahead of (i.e., east of) or behind (i.e., west of) UTC. The first two digits indicate the number of hours difference from Universal Time, and the last two digits indicate the number of minutes difference from Universal Time. Note that this agrees with the RFC5322 format for time zone offsets, not the ISO 8601 format. The local time zone MUST be used for bytimeabsolute if the :zone argument is omitted.

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 is important to note 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 can be determined. Additionally, note that bytimerelative values can be negative, making it necessary to either perform additional checks or else use a comparator that, unlike i;ascii-numeric, is capable of handling signed integers.

Examples

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 allotted time. Note the additional check to see if the value is negative:

require ["envelope", "envelope-deliverby", "relational",

        "comparator-i;ascii-numeric"];

1. Check to see if this message didn't make it in the time allotted by
2. the originator.

if anyof (envelope :contains "bytimerelative" "-",

         envelope :value "eq" :comparator "i;ascii-numeric"
                  "bytimerelative" "0")

{

   # do whatever

}

This operation can be done more simply if the date RFC5260 and variables RFC5229 extensions are available:

require ["envelope", "envelope-deliverby", "relational", "date",

        "variables"];

1. Check to see if this message didn't make it in the time allotted by
2. the originator.

if currentdate :matches "iso8601" "*" {

   set "cdate" "${0}";
   if envelope :value "ge" "bytimeabsolute" "${cdate}" {
       # do whatever
   }

}

Note that there is no need to force the use of a particular time zone since both currentdate and the bytimeabsolute value are required to default to the local time zone. A similar check could be written using :zone if the action taken depends on having the by-time represented in a particular zone:

require ["envelope", "envelope-deliverby", "relational", "date",

        "variables"];

1. If the message didn't make it in time, file it according to when it
2. should have been received

if envelope :matches :zone "+0000" "bytimeabsolute" "*T*:*:*" {

   set "bdate" "${0}";
   set "bhour" "${2}";
   if currentdate :zone "+0000" :value "lt" "iso8601" "${bdate}")
       fileinto "missed-${bhour}";
   }

}

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 ABNF 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.

MAIL FROM Address Selection

RFC 5228 does not require that any particular envelope sender address be associated with redirected messages. However, the redirect-dsn extension isn't terribly useful if the place where the delivery status notifications are sent isn't known. Accordingly, when either

notify or :ret is specified and the envelope sender address isn't

empty, implementations MUST set the envelope sender address to the address of the sieve owner.

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:

require ["copy", "redirect-dsn"];

1. Make a private copy of messages from [email protected]

if address "from" "[email protected]" {

   redirect :copy :notify "NEVER" "[email protected]";

}

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 [:bytimerelative <rlimit: number> /

                  :bytimeabsolute <alimit:string>
                  [:bymode "notify"|"return"] [:bytrace]]
                 <address: string>

bytimerelative specifies the number of seconds within which the

message should be delivered. This parameter does not allow specification of negative values; it should not be necessary to specify such values in this context. :bytimeabsolute specifies an absolute time limit on delivery. The limit in this case is specified in the restricted ISO 8601 format specified by the date-time ABNF production given in RFC3339.

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. :bytrace, if specified, activates message tracing.

The semantics of delivery time limits and these parameters are specified and discussed at length in RFC2852.

It is an error to specify either :bymode or :bytrace without either

bytimeabsolute or :bytimerelative.

When these arguments are specified, they are used to construct the corresponding BY ESMTP MAIL FROM parameter. The :bytimeabsolute or

bytimerelative 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 the redirected 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.

MAIL FROM Address Selection

RFC 5228 does not require that any particular envelope sender address be associated with redirected messages. However, the redirect- deliverby extension, like the redirect-dsn extension, isn't terribly useful if the place where any delivery status notifications are sent isn't known. Accordingly, when either :bytimeabsolute or

bytimerelative is specified and the envelope sender address isn't

empty, implementations MUST set the envelope sender address to the address of the sieve owner.

Example

The obvious use of "redirect-deliverby" is to specify a limit on delivery attempts for a redirected message:

require ["copy", "redirect-deliverby"];

1. Send a copy to my cell phone, time out after 10 minutes

if address "from" "[email protected]" {

   redirect :copy :bytimerelative 600 "[email protected]";

}

Limits on delivery after a particular time of day may also be constructed:

require ["copy", "redirect-deliverby", "date", "variables",

        "relational", "comparator-i;ascii-numeric"];

1. Send a copy to my cell phone to be delivered before 10PM

if currentdate :value "lt"

              :comparator "i;ascii-numeric" "hour" "22"

{

   if currentdate :matches "date" "*" {set "date" "${0}";}
   if currentdate :matches "zone" "*" {set "zone" "${0}";}
   redirect :copy :bytimeabsolute "${date}T20:00:00${zone}"
            :bymode "return" "[email protected]";

}

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 that 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.

IANA Considerations

The following template specifies the IANA registration of the Sieve extension specified in this document:

To: [email protected]
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 6009
Contact address: Sieve discussion list <[email protected]>

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 6009
Contact address: Sieve discussion list <[email protected]>

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 6009
Contact address: Sieve discussion list <[email protected]>

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 6009
Contact address: Sieve discussion list <[email protected]>

This information has been added to the list of Sieve extensions
available from http://www.iana.org.

10. References

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.

RFC3339 Klyne, G., Ed. and C. Newman, "Date and Time on the

          Internet: Timestamps", RFC 3339, July 2002.

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.

RFC5322 Resnick, P., Ed., "Internet Message Format", RFC 5322,

          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.

RFC5229 Homme, K., "Sieve Email Filtering: Variables Extension",

          RFC 5229, January 2008.

RFC5260 Freed, N., "Sieve Email Filtering: Date and Index

          Extensions", RFC 5260, July 2008.

Appendix A. Acknowledgements

Cyrus Daboo, Derek Diget, Philip Guenther, Arnt Gulbrandsen, Tero Kivinen, Barry Leiba, Andrew McKeon, Alexey Melnikov, Chris Newman, Aaron Stone, and Alexandros Vellis provided helpful suggestions and corrections.

Author's Address

Ned Freed Oracle 800 Royal Oaks Monrovia, CA 91016-6347 USA

EMail: [email protected]