Network Working Group N. Freed
Internet-Draft Sun Microsystems
Expires: May 17, 2007 November 13, 2006
Sieve Email Filtering: Environment and Ihave Extensions
draft-freed-sieve-environment-ihave-00
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Abstract
This document describes the "environment" and "ihave" extensions to
the Sieve email filtering language. The "environment" extension
gives Sieve access to information about the environment where the
Sieve interpreter is running. The "ihave" extension provides a means
to write scripts that can take advantage of optional Sieve features
but can still run when those optional features are not available.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. Capability Identifiers . . . . . . . . . . . . . . . . . . . . 3
4. Environment Test . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Standard Environment Items . . . . . . . . . . . . . . . . 4
4.2. Vendor-defined Environment Items . . . . . . . . . . . . . 5
4.3. IANA Registration of Environment Items . . . . . . . . . . 5
4.3.1. Template for Environment Registrations . . . . . . . . 5
4.3.2. Initial Environment Item Registrations . . . . . . . . 6
5. Ihave Test . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative references . . . . . . . . . . . . . . . . . . . 8
8.2. Informative references . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
Sieve [I-D.ietf-sieve-3028bis] 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 or otherwise operated in different contexts.
A large number of sieve extensions have already been defined and more
are sure to be created over time. Sieve's require clause is used to
specify the extensions a particular sieve needs; an error results if
the script's require clause calls for an extension that isn't
available. This mechanism is sufficient in most situations.
However, there can be cases where a script may be able to take
advantage of an extension if it is available but can still function
if it is not, possibly with some degradation of capabilities.
The "ihave" extension provides a means to write scripts that make use
of other extensions only when they are actually available. Ihave
defines a new ihave test that takes a list of capability names as an
argument and succeeds if all of the those capabilities are present.
Additionally, specification of the "ihave" extension in the require
clause disables parse-time checking of extension use in scripts; run-
time checking must be used instead.
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 RFC 2119 [RFC2119].
The terms used to describe the various components of the Sieve
language are taken from [I-D.ietf-sieve-3028bis] section 1.1.
3. Capability Identifiers
The capability strings associated with the two extensions defined in
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this document are "environment" and "ihave".
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
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 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 [I-D.ietf-sieve-3431bis] 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. Standard Environment Items
The initial set of standardized environment items is as follows:
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"name" => the product name associated with the Sieve interpreter
"version" => the product version associated with the Sieve
interpreter
"host" => the fully-qualified domain name of the host where the
Sieve script is executing
"domain" => the primary DNS domain associated with the Sieve
execution context, usually but not always a proper
suffix of the host name
"place" => 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 "UA", meaning evaluation is occurring after final
delivery.
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.
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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]
4.3.2. Initial Environment Item Registrations
TBD once the initial list has been determined.
5. Ihave Test
Usage: ihave <capabilities: string-list>
The ihave test provides a means for Sieve scripts to test for the
existence of a given extension prior to actually using it. The
capabilities argument to ihave is the same as the similarly-named
argument to the require control statement: It specifies the names of
one or more Sieve extensions or comparators.
Unlike most Sieve tests, ihave accepts no match or comparator
arguments. The type of match for ihave is always ":is" and the
comparator is always "i;ascii-casemap".
The strings in the capabilities list are constant strings in context
of Sieve variables [I-D.ietf-sieve-variables]. It is an error to
pass a non-constant string as an argument to ihave.
The Sieve base specification demands that that all Sieve extensions
used in a given script be specified in the initial require control
statement. It is an error for a script to call for extensions the
interpreter doesn't support or to attempt to use extensions that have
not been listed in the script's require clause. Use of ihave changes
Sieve interpreter behavior and the underlying requirements in the
following ways:
1. Use of a given extension is allowed inside of a block enclosed by
an ihave test on that extension just as if the extension had been
specified in the script's require clause. The extension cannot
be used outside of such a block and a runtime error MUST be
generated if such usage is attempted.
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2. Sieve interpreters normally have the option of checking extension
use at either parse time or execution time. The specification of
"ihave" in a script's require clause changes this behavior:
Scripts MUST either defer extension checking to run time or else
take the presence of ihave tests into account.
3. Although it makes little sense to do so, an extension can be
specified in both the require control statement and in an ihave
test. If this is done the ihave test will always return true.
4. Using ihave to set a variable to a particular value and then
testing that variable in another block is not permitted as it
unduly complicates parse time analysis of scripts.
Ihave is designed to be used with extensions that add tests, actions,
or comparators. It MUST NOT be used with extensions that change how
the content of Sieve scripts are interpreted such as the variables
extension [I-D.ietf-sieve-variables]
6. 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. Ihave, on the other hand, reveals nothing that
cannot be found out by trying different require clauses.
All of the security considerations given in the base Sieve
specification also apply to these extensions.
7. IANA Considerations
This specification defines a new IANA registry for Sieve environment
item names. The specifics of this registry are given in Section 4.3.
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The following templates specify the IANA registrations of the two
Sieve extensions specified in this document:
To: iana@iana.org
Subject: Registration of new Sieve extensions
Capability name: ENVIRONMENT
Capability keyword: environment
Capability arguments: N/A
Standards Track/IESG-approved experimental RFC number: this RFC
Person and email address to contact for further information:
Ned Freed
E-Mail: ned.freed@mrochek.com
Capability name: IHAVE
Capability keyword: ihave
Capability arguments: N/A
Standards Track/IESG-approved experimental RFC number: this RFC
Person and email address to contact for further information:
Ned Freed
E-Mail: ned.freed@mrochek.com
This information should be added to the list of sieve extensions
given on http://www.iana.org/assignments/sieve-extensions.
8. References
8.1. Normative references
[I-D.ietf-sieve-3028bis]
Guenther, P. and T. Showalter, "Sieve: An Email Filtering
Language", draft-ietf-sieve-3028bis-09 (work in progress),
August 2006, <http://www.ietf.org/internet-drafts/
draft-ietf-sieve-3028bis-09.txt>.
[I-D.ietf-sieve-3431bis]
Segmuller, W. and B. Leiba, "Sieve Extension: Relational
Tests", draft-ietf-sieve-3431bis-04 (work in progress),
December 2005, <http://www.ietf.org/internet-drafts/
draft-ietf-sieve-3431bis-04.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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8.2. Informative references
[I-D.ietf-sieve-variables]
Homme, K., "Sieve Mail Filtering Language: Variables
Extension", draft-ietf-sieve-variables-08 (work in
progress), December 2005, <http://www.ietf.org/
internet-drafts/draft-ietf-sieve-variables-08.txt>.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
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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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