Network Working Group C. Daboo
Internet-Draft Cyrusoft International, Inc.
Expires: August 4, 2004 February 4, 2004
SIEVE Email Filtering: MIME Extension
draft-daboo-sieve-mime-00
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document describes the SIEVE Email Filtering "mime" extension
which adds a new test for testing the values of MIME headers in a
message.
Open Issues (will be removed prior to publication as an RFC)
a. How to deal with MIME encoding/splitting of parameters, i18n etc
Change History (to be removed prior to publication as an RFC)
Changes:
a. Initial draft.
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Table of Contents
1. Introduction and Overview . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. SIEVE MIME Extension . . . . . . . . . . . . . . . . . . . . . 3
3.1 General Considerations . . . . . . . . . . . . . . . . . . . . 3
3.2 Test "mime" . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5.1 mime registration . . . . . . . . . . . . . . . . . . . . . . 5
References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . 7
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1. Introduction and Overview
The SIEVE Email Filtering [RFC3028] specification currently does not
provide a way to test the values of MIME [RFC2045] part headers
within a message. Currently, all that can be done is a standard
"header" test against the top-level message headers (and thus the
top-level MIME part of the message). However, it is handy to be able
to check for values in any MIME part headers, or check for the
presence of specific MIME types etc. This extension introduces a new
"mime" test that allows the values of every MIME part header to be
tested.
2. Conventions Used in This Document
Conventions for notations are as in [RFC3028] section 1.1, including
use of [RFC2119].
3. SIEVE MIME Extension
3.1 General Considerations
SIEVE implementations that implement the "mime" test have an
identifier of "mime" for use with the capability mechanism. If the
"mime" test is used in a SIEVE script, the corresponding capability
item MUST appear in the script's "require" statement. Like the
"header" test in [RFC3028], folding of long header lines (as
described in [RFC2822]) is removed prior to interpretation of the
data.
3.2 Test "mime"
Syntax: mime [COMPARATOR] [MATCH-TYPE]
<header-names: string-list>
[<parameter-names: string-list>]
<key-list: string-list>
The "mime" test evaluates to true if any MIME header name, or any
parameter within a MIME header name, matches any key. The type of
match is specified by the optional match argument, which defaults to
":is" if not provided, as specified in section 2.6 of [RFC3028].
If no parameter-names argument is present, then the entire content of
the headers specified in the header-names argument is evaluated. So
if a message contained the MIME header:
Content-Type: image/jpeg; filename="example.jpg"
these tests on that MIME header evaluate as follows:
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mime :contains ["Content-Type"] ["image"] => true
mime :contains ["Content-Type"] ["jpg"] => true
mime :contains ["Content-Type"] ["filename"] => true
mime :contains ["Content-Type"] ["gif"] => false
If the parameter-names argument is present, then only the content of
matching MIME parameters in the specified headers are evaluated. So
if a message contained the MIME header:
Content-Type: image/jpeg; filename="example.jpg"
these tests on that MIME header evaluate as follows:
mime :contains ["Content-Type"] ["filename"] ["image"] => false
mime :contains ["Content-Type"] ["filename"] ["jpg"] => true
mime :contains ["Content-Type"] ["filename"] ["filename"] => false
mime :contains ["Content-Type"] ["filename"] ["gif"] => false
mime :contains ["Content-Type"] ["name"] ["jpg"] => false
If the parameter-names argument is present, but contains a single
empty string, then the content of specified MIME header, excluding
any parameters, will be evaluated. So if a message contained the MIME
header:
Content-Type: image/jpeg; filename="example.jpg"
these tests on that MIME header evaluate as follows:
mime :contains ["Content-Type"] [""] ["image"] => true
mime :contains ["Content-Type"] [""] ["jpg"] => false
mime :contains ["Content-Type"] [""] ["filename"] => false
mime :contains ["Content-Type"] [""] ["gif"] => false
Like the "header" test in [RFC3028], this test returns true if any
combination of the header-names, parameters-names and key-list
arguments match.
Like the "header" test in [RFC3028], if a MIME header listed in the
header-names argument exists, it contains the null key (""). However,
if the named header is not present, it does not contain the null key.
So if a message contained the MIME header:
Content-Caffeine: C8H10N4O2
these tests on that header evaluate as follows:
mime :is ["Content-Caffeine"] [""] => false
mime :contains ["Content-Caffeine"] [""] => true
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A similar behaviour applies to MIME parameters specified by the
parameter-names argument:
Content-Caffeine: C8H10N4O2; param1=example
these tests on that parameter evaluate as follows:
mime :is ["Content-Caffeine"] ["param1"] [""] => false
mime :contains ["Content-Caffeine"] ["param1"] [""] => true
4. Security Considerations
The "mime" extension does not raise any security considerations that
are not present in the base [RFC3028] protocol, and these issues are
discussed in [RFC3028].
5. IANA Considerations
The following template specifies the IANA registration of the Sieve
extension specified in this document:
5.1 mime registration
To: iana@iana.org
Subject: Registration of new Sieve extension
Capability name: mime
Capability keyword: mime
Capability arguments:
mime [COMPARATOR] [MATCH-TYPE]
<header-names: string-list>
[<parameter-names: string-list>]
<key-list: string-list>
Standards Track/IESG-approved experimental RFC number: this RFC
Person and email address to contact for further information:
Cyrus Daboo
Cyrusoft International, Inc.
5001 Baum Blvd., Suite 780,
Pittsburgh, PA 15213
U.S.A.
<mailto:daboo@cyrusoft.com>
This information should be added to the list of sieve extensions
given on http://www.iana.org/assignments/sieve-extensions.
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References
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April
2001.
[RFC3028] Showalter, T., "Sieve: A Mail Filtering Language", RFC
3028, January 2001.
Author's Address
Cyrus Daboo
Cyrusoft International, Inc.
5001 Baum Blvd.
Suite 780
Pittsburgh, PA 15213
US
EMail: daboo@cyrusoft.com
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