💾 Archived View for gemini.bortzmeyer.org › rfc-mirror › rfc5173.txt captured on 2024-02-05 at 11:21:38.
⬅️ Previous capture (2021-11-30)
-=-=-=-=-=-=-
Network Working Group J. Degener
Request for Comments: 5173 P. Guenther
Updates: 5229 Sendmail, Inc.
Category: Standards Track April 2008
Sieve Email Filtering: Body Extension
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document defines a new command for the "Sieve" email filtering
language that tests for the occurrence of one or more strings in the
body of an email message.
Degener & Guenther Standards Track [Page 1]
RFC 5173 Sieve Email Filtering: Body Extension April 2008
1. Introduction
The "body" test checks for the occurrence of one or more strings in
the body of an email message. Such a test was initially discussed
for the [SIEVE] base document, but was subsequently removed because
it was thought to be too costly to implement.
Nevertheless, several server vendors have implemented some form of
the "body" test.
This document reintroduces the "body" test as an extension, and
specifies its syntax and semantics.
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 [KEYWORDS].
Conventions for notations are as in [SIEVE] Section 1.1, including
the use of the "Usage:" label for the definition of text and tagged
argument syntax.
The rules for interpreting the grammar are defined in [SIEVE] and
inherited by this specification. In particular, readers of this
document are reminded that according to [SIEVE] Sections 2.6.2 and
2.6.3, optional arguments such as COMPARATOR and MATCH-TYPE can
appear in any order.
3. Capability Identifier
The capability string associated with the extension defined in this
document is "body".
4. Test body
Usage: "body" [COMPARATOR] [MATCH-TYPE] [BODY-TRANSFORM]
<key-list: string-list>
The body test matches content in the body of an email message, that
is, anything following the first empty line after the header. (The
empty line itself, if present, is not considered to be part of the
body.)
The COMPARATOR and MATCH-TYPE keyword parameters are defined in
[SIEVE]. As specified in Sections 2.7.1 and 2.7.3 of [SIEVE], the
default COMPARATOR is "i;ascii-casemap" and the default MATCH-TYPE is
":is".
Degener & Guenther Standards Track [Page 2]
RFC 5173 Sieve Email Filtering: Body Extension April 2008
The BODY-TRANSFORM is a keyword parameter that governs how a set of
strings to be matched against are extracted from the body of the
message. If a message consists of a header only, not followed by an
empty line, then that set is empty and all "body" tests return false,
including those that test for an empty string. (This is similar to
how the "header" test always fails when the named header fields
aren't present.) Otherwise, the transform must be followed as
defined below in Section 5.
Note that the transformations defined here do *not* match against
each line of the message independently, so the strings will usually
contain CRLFs. How these can be matched is governed by the
comparator and match-type. For example, with the default comparator
of "i;ascii-casemap", they can be included literally in the key
strings, or be matched with the "*" or "?" wildcards of the :matches
match-type, or be skipped with :contains.
5. Body Transform
Prior to matching content in a message body, "transformations" can be
applied that filter and decode certain parts of the body. These
transformations are selected by a "BODY-TRANSFORM" keyword parameter.
Usage: ":raw"
/ ":content" <content-types: string-list>
/ ":text"
The default transformation is :text.
5.1. Body Transform ":raw"
The ":raw" transform matches against the entire undecoded body of a
message as a single item.
If the specified body-transform is ":raw", the [MIME] structure of
the body is irrelevant. The implementation MUST NOT remove any
transfer encoding from the message, MUST NOT refuse to filter
messages with syntactic errors (unless the environment it is part of
rejects them outright), and MUST treat multipart boundaries or the
MIME headers of enclosed body parts as part of the content being
matched against, instead of MIME structures to interpret.
Degener & Guenther Standards Track [Page 3]
RFC 5173 Sieve Email Filtering: Body Extension April 2008
Example:
require "body";
# This will match a message containing the literal text
# "MAKE MONEY FAST" in body parts (ignoring any
# content-transfer-encodings) or MIME headers other than
# the outermost RFC 2822 header.
if body :raw :contains "MAKE MONEY FAST" {
discard;
}
5.2. Body Transform ":content"
If the body transform is ":content", the MIME parts that have the
specified content types are matched against independently.
If an individual content type begins or ends with a '/' (slash) or
contains multiple slashes, then it matches no content types.
Otherwise, if it contains a slash, then it specifies a full
<type>/<subtype> pair, and matches only that specific content type.
If it is the empty string, all MIME content types are matched.
Otherwise, it specifies a <type> only, and any subtype of that type
matches it.
The search for MIME parts matching the :content specification is
recursive and automatically descends into multipart and
message/rfc822 MIME parts. All MIME parts with matching types are
searched for the key strings. The test returns true if any
combination of a searched MIME part and key-list argument match.
If the :content specification matches a multipart MIME part, only the
prologue and epilogue sections of the part will be searched for the
key strings, treating the entire prologue and the entire epilogue as
separate strings; the contents of nested parts are only searched if
their respective types match the :content specification.
If the :content specification matches a message/rfc822 MIME part,
only the header of the nested message will be searched for the key
strings, treating the header as a single string; the contents of the
nested message body parts are only searched if their content type
matches the :content specification.
For other MIME types, the entire part will be searched as a single
string.
Degener & Guenther Standards Track [Page 4]
RFC 5173 Sieve Email Filtering: Body Extension April 2008
(Matches against container types with an empty match string can be
useful as tests for the existence of such parts.)
Example:
From: Whomever
To: Someone
Date: Whenever
Subject: whatever
Content-Type: multipart/mixed; boundary=outer
& This is a multi-part message in MIME format.
&
--outer
Content-Type: multipart/alternative; boundary=inner
& This is a nested multi-part message in MIME format.
&
--inner
Content-Type: text/plain; charset="us-ascii"
$ Hello
$
--inner
Content-Type: text/html; charset="us-ascii"
% <html><body>Hello</body></html>
%
--inner--
&
& This is the end of the inner MIME multipart.
&
--outer
Content-Type: message/rfc822
! From: Someone Else
! Subject: hello request
$ Please say Hello
$
--outer--
&
& This is the end of the outer MIME multipart.
Degener & Guenther Standards Track [Page 5]
RFC 5173 Sieve Email Filtering: Body Extension April 2008
In the above example, the '&', '