Network Working Group N. Freed
Internet-Draft Sun Microsystems
Expires: August 28, 2008 February 25, 2008
Sieve Email Filtering: Environment Extension
draft-freed-sieve-environment-02
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Abstract
This document describes the "environment" extension to the Sieve
email filtering language. The "environment" extension gives Sieve
access to information about the environment where the Sieve
interpreter is running.
Change History (to be removed prior to publication as an RFC
Changed one place string result from "UA" to "MUA".
Updated the IANA registration template.
Moved the ihave extension to a separate document.
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Added remote-host and remote-ip environment items to the initial set.
Updated references.
1. 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.
Although sieve is intended to be independent of access protocol, mail
architecture, and operating system, in some cases it is useful to
allow scripts to access information about their execution context.
The "environment" extension provides a new environment test that can
be used to implement scripts that behave differently when moved from
one system to another, when messages arrive from different remote
sources or when otherwise operated in different contexts.
2. Conventions used in this document
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14 [RFC2119].
The terms used to describe the various components of the Sieve
language are taken from [RFC5228] section 1.1.
3. Capability Identifiers
The capability string associated with the extension defined in this
document is "environment".
4. Environment Test
Usage: environment [COMPARATOR] [MATCH-TYPE]
<name: string>
<key-list: string-list>
The environment test retrieves the item of environment information
specified by the name string and matches it to the values specified
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in the key-list. The test succeeds if a match occurs. The type of
match defaults to ":is" and the default comparator is "i;ascii-
casemap".
The current message is not a direct source of information for the
environment test; the item of information specified by the name
string is extracted from the script's operating environment and key-
list comes from the script.
The environment test MUST fail unconditionally if the specified
information item does not exist. A script MUST NOT fail with an
error if the item does not exist. This allows scripts to be written
that handle nonexistent items gracefully.
The "relational" extension [RFC5231] adds a match type called
":count". The count of an environment test is 0 if the environment
information returned is the empty string, or 1 otherwise.
Environment items can be standardized or vendor-defined. An IANA
registry is defined for both types of items.
4.1. Initial Standard Environment Items
The initial set of standardized environment items is as follows:
"domain" => The primary DNS domain associated with the Sieve
execution context, usually but not always a proper
suffix of the host name.
"evaluation-time"
=> Sieve processing is normally performing around or after
the time of final delivery. This item provides
additional information about the relationship to final
delivery. Possible return values are "MTA", meaning the
Sieve is being evaluated before final delivery, "MDA",
meaning evaluation is occurring during final delivery",
and "MUA", meaning evaluation is occurring after final
delivery.
"host" => The fully-qualified domain name of the host where the
Sieve script is executing.
"name" => The product name associated with the Sieve interpreter.
"remote-host"
=> Host name of remote SMTP client, if applicable and
available.
"remote-ip"
=> IP address of remote SMTP client, if applicable and
available.
"version" => The product version associated with the Sieve
interpreter.
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Implementations SHOULD support as many of the items on this initial
list as possible. Additional standardized items can only be defined
in standards-track or experimental RFCs.
4.2. Vendor-defined Environment Items
Environment item names beginning with "vnd." represent vendor-defined
extensions. Such extensions are not defined by Internet standards or
RFCs, but are still registered with IANA in order to prevent
conflicts. Environment item names starting with "vnd." SHOULD be
followed by the name of the vendor and product, such as
"vnd.acme.rocket-sled-status".
4.3. IANA Registration of Environment Items
A registry of environment items is provided by IANA. Item names may
be registered on a first-come, first-served basis. Extensions
designed for interoperable use SHOULD be defined as standards track
or IESG approved experimental RFCs.
4.3.1. Template for Environment Registrations
The following template is to be used for registering new Sieve
environment item names with IANA.
To: iana@iana.org
Subject: Registration of new Sieve environment item
Item name: [the string for use in the 'environment' test]
Description: [a brief description of the semantics of the
value the item returns]
RFC number: [for extensions published as RFCs]
Contact address: [email and/or physical address to contact for
additional information]
Multiple items and descripions MAY be specified in a single
registration request. Both standardized and vender-defined items use
this form.
5. Security Considerations
The environment extension may be used to obtain information about the
system the sieve implementation is running on. This information in
turn may reveal details about service provider or enterprise
infrastructure.
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All of the security considerations given in the base Sieve
specification also apply to this extension.
6. 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 extension
Capability name: environment
Description: The "environment" extension provides a new
environment test that can be used to implement
scripts that behave differently when moved
from one system to another or otherwise
operated in different contexts.
RFC number: RFC XXXX
Contact address: Sieve discussion list <ietf-mta-filters@imc.org>
This specification also defines a new IANA registry for Sieve
environment item names. The specifics of this registry are given in
Section 4.3. The initial contents of the registry are given in the
following section.
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6.1. Initial Environment Item Registrations
The following template specifies the initial IANA registrations for
the environment items defined in this document:
To: iana@iana.org
Subject: Registration of new Sieve environment items
Capability name: domain
Description: The primary DNS domain associated with the Sieve
execution context, usually but not always a
proper suffix of the host name.
Capability name: evaluation-time
Description: Time at which this Sieve processing is being
performed.
Capability name: host
Description: The fully-qualified domain name of the host
where the Sieve script is executing.
Capability name: name
Description: The product name associated with the Sieve
interpreter.
Capability name: remote-host
Description: Host name of remote SMTP client, if applicable
and available.
Capability name: remote-ip
Description: IP address of remote SMTP client, if applicable
and available.
Capability name: version
Description: The product version associated with the Sieve
interpreter.
RFC number: RFC XXXX
Contact address: Sieve discussion list <ietf-mta-filters@imc.org>
7. References
7.1. Normative references
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[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.
7.2. Informative references
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
Author's Address
Ned Freed
Sun Microsystems
3401 Centrelake Drive, Suite 410
Ontario, CA 92761-1205
USA
Phone: +1 909 457 4293
Email: ned.freed@mrochek.com
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