Sieve Email Filtering: Editheader Extension
RFC 5293
Network Working Group J. Degener
Request for Comments: 5293 P. Guenther
Category: Standards Track Sendmail, Inc.
August 2008
Sieve Email Filtering: Editheader 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 two new actions for the "Sieve" email filtering
language that add and delete email header fields.
1. Introduction
Email header fields are a flexible and easy-to-understand means of
communication between email processors. This extension enables sieve
scripts to interact with other components that consume or produce
header fields by allowing the script to delete and add header fields.
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 Section 1.1 of [SIEVE], including
use of the "Usage:" label for the definition of action and tagged
arguments syntax.
The term "header field" is used here as in [IMAIL] to mean a logical
line of an email message header.
3. Capability Identifier
The capability string associated with the extension defined in this
document is "editheader".
Degener & Guenther Standards Track [Page 1]
RFC 5293 Sieve Email Filtering: Editheader Extension August 2008
4. Action addheader
Usage: "addheader" [":last"] <field-name: string> <value: string>
The addheader action adds a header field to the existing message
header. If the field-name is not a valid 7-bit US-ASCII header field
name, as described by the [IMAIL] "field-name" nonterminal syntax
element, the implementation MUST flag an error. The addheader action
does not affect Sieve's implicit keep.
If the specified field value does not match the [IMAIL]
"unstructured" nonterminal syntax element or exceeds a length limit
set by the implementation, the implementation MUST either flag an
error or encode the field using folding white space and the encodings
described in [MIME3] or [MIMEPARAM] to be compliant with [IMAIL].
An implementation MAY impose a length limit onto the size of the
encoded header field; such a limit MUST NOT be less than 998
characters, not including the terminating CRLF supplied by the
implementation.
By default, the header field is inserted at the beginning of the
existing message header. If the optional flag ":last" is specified,
it is appended at the end.
Example:
/* Don't redirect if we already redirected */
if not header :contains "X-Sieve-Filtered"
["<kim@job.example.com>", "<kim@home.example.com>"]
{
addheader "X-Sieve-Filtered" "<kim@job.example.com>";
redirect "kim@home.example.com";
}
5. Action deleteheader
Usage: "deleteheader" [":index" <fieldno: number> [":last"]]
[COMPARATOR] [MATCH-TYPE]
<field-name: string>
[<value-patterns: string-list>]
By default, the deleteheader action deletes all occurrences of the
named header field. The deleteheader action does not affect Sieve's
implicit keep.
Degener & Guenther Standards Track [Page 2]
RFC 5293 Sieve Email Filtering: Editheader Extension August 2008
The field-name is mandatory and always matched as a case-insensitive
US-ASCII string. If the field-name is not a valid 7-bit header field
name as described by the [IMAIL] "field-name" nonterminal syntax
element, the implementation MUST flag an error.
The value-patterns, if specified, restrict which occurrences of the
header field are deleted to those whose values match any of the
specified value-patterns, the matching being according to the match-
type and comparator and performed as if by the "header" test. In
particular, leading and trailing whitespace in the field values is
ignored. If no value-patterns are specified, then the comparator and
match-type options are silently ignored.
If :index <fieldno> is specified, the attempts to match a value are
limited to the <fieldno> occurrence of the named header field,
beginning at 1, the first named header field. If :last is specified,
the count is backwards; 1 denotes the last named header field, 2 the
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