5ecd557dfb
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>
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72 KiB
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2020 lines
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Network Working Group T. Showalter
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Request for Comments: 3028 Mirapoint, Inc.
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Category: Standards Track January 2001
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Sieve: A Mail Filtering Language
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Status of this Memo
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This document specifies an Internet standards track protocol for the
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Internet community, and requests discussion and suggestions for
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improvements. Please refer to the current edition of the "Internet
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Official Protocol Standards" (STD 1) for the standardization state
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and status of this protocol. Distribution of this memo is unlimited.
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Copyright Notice
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Copyright (C) The Internet Society (2001). All Rights Reserved.
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Abstract
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This document describes a language for filtering e-mail messages at
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time of final delivery. It is designed to be implementable on either
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a mail client or mail server. It is meant to be extensible, simple,
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and independent of access protocol, mail architecture, and operating
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system. It is suitable for running on a mail server where users may
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not be allowed to execute arbitrary programs, such as on black box
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Internet Message Access Protocol (IMAP) servers, as it has no
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variables, loops, or ability to shell out to external programs.
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Table of Contents
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1. Introduction ........................................... 3
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1.1. Conventions Used in This Document ..................... 4
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1.2. Example mail messages ................................. 4
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2. Design ................................................. 5
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2.1. Form of the Language .................................. 5
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2.2. Whitespace ............................................ 5
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2.3. Comments .............................................. 6
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2.4. Literal Data .......................................... 6
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2.4.1. Numbers ............................................... 6
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2.4.2. Strings ............................................... 7
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2.4.2.1. String Lists .......................................... 7
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2.4.2.2. Headers ............................................... 8
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2.4.2.3. Addresses ............................................. 8
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2.4.2.4. MIME Parts ............................................ 9
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2.5. Tests ................................................. 9
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2.5.1. Test Lists ............................................ 9
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Showalter Standards Track [Page 1]
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RFC 3028 Sieve: A Mail Filtering Language January 2001
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2.6. Arguments ............................................. 9
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2.6.1. Positional Arguments .................................. 9
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2.6.2. Tagged Arguments ...................................... 10
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2.6.3. Optional Arguments .................................... 10
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2.6.4. Types of Arguments .................................... 10
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2.7. String Comparison ..................................... 11
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2.7.1. Match Type ............................................ 11
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2.7.2. Comparisons Across Character Sets ..................... 12
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2.7.3. Comparators ........................................... 12
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2.7.4. Comparisons Against Addresses ......................... 13
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2.8. Blocks ................................................ 14
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2.9. Commands .............................................. 14
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2.10. Evaluation ............................................ 15
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2.10.1. Action Interaction .................................... 15
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2.10.2. Implicit Keep ......................................... 15
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2.10.3. Message Uniqueness in a Mailbox ....................... 15
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2.10.4. Limits on Numbers of Actions .......................... 16
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2.10.5. Extensions and Optional Features ...................... 16
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2.10.6. Errors ................................................ 17
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2.10.7. Limits on Execution ................................... 17
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3. Control Commands ....................................... 17
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3.1. Control Structure If .................................. 18
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3.2. Control Structure Require ............................. 19
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3.3. Control Structure Stop ................................ 19
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4. Action Commands ........................................ 19
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4.1. Action reject ......................................... 20
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4.2. Action fileinto ....................................... 20
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4.3. Action redirect ....................................... 21
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4.4. Action keep ........................................... 21
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4.5. Action discard ........................................ 22
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5. Test Commands .......................................... 22
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5.1. Test address .......................................... 23
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5.2. Test allof ............................................ 23
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5.3. Test anyof ............................................ 24
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5.4. Test envelope ......................................... 24
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5.5. Test exists ........................................... 25
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5.6. Test false ............................................ 25
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5.7. Test header ........................................... 25
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5.8. Test not .............................................. 26
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5.9. Test size ............................................. 26
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5.10. Test true ............................................. 26
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6. Extensibility .......................................... 26
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6.1. Capability String ..................................... 27
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6.2. IANA Considerations ................................... 28
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6.2.1. Template for Capability Registrations ................. 28
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6.2.2. Initial Capability Registrations ...................... 28
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6.3. Capability Transport .................................. 29
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7. Transmission ........................................... 29
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Showalter Standards Track [Page 2]
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RFC 3028 Sieve: A Mail Filtering Language January 2001
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8. Parsing ................................................ 30
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8.1. Lexical Tokens ........................................ 30
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8.2. Grammar ............................................... 31
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9. Extended Example ....................................... 32
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10. Security Considerations ................................ 34
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11. Acknowledgments ........................................ 34
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12. Author's Address ....................................... 34
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13. References ............................................. 34
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14. Full Copyright Statement ............................... 36
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1. Introduction
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This memo documents a language that can be used to create filters for
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electronic mail. It is not tied to any particular operating system or
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mail architecture. It requires the use of [IMAIL]-compliant
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messages, but should otherwise generalize to many systems.
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The language is powerful enough to be useful but limited in order to
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allow for a safe server-side filtering system. The intention is to
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make it impossible for users to do anything more complex (and
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dangerous) than write simple mail filters, along with facilitating
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the use of GUIs for filter creation and manipulation. The language is
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not Turing-complete: it provides no way to write a loop or a function
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and variables are not provided.
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Scripts written in Sieve are executed during final delivery, when the
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message is moved to the user-accessible mailbox. In systems where
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the MTA does final delivery, such as traditional Unix mail, it is
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reasonable to sort when the MTA deposits mail into the user's
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mailbox.
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There are a number of reasons to use a filtering system. Mail
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traffic for most users has been increasing due to increased usage of
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e-mail, the emergence of unsolicited email as a form of advertising,
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and increased usage of mailing lists.
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Experience at Carnegie Mellon has shown that if a filtering system is
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made available to users, many will make use of it in order to file
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messages from specific users or mailing lists. However, many others
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did not make use of the Andrew system's FLAMES filtering language
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[FLAMES] due to difficulty in setting it up.
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Because of the expectation that users will make use of filtering if
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it is offered and easy to use, this language has been made simple
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enough to allow many users to make use of it, but rich enough that it
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can be used productively. However, it is expected that GUI-based
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editors will be the preferred way of editing filters for a large
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number of users.
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Showalter Standards Track [Page 3]
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RFC 3028 Sieve: A Mail Filtering Language January 2001
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1.1. Conventions Used in This Document
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In the sections of this document that discuss the requirements of
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various keywords and operators, the following conventions have been
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adopted.
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The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and
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"MAY" in this document are to be interpreted as defined in
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[KEYWORDS].
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Each section on a command (test, action, or control structure) has a
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line labeled "Syntax:". This line describes the syntax of the
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command, including its name and its arguments. Required arguments
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are listed inside angle brackets ("<" and ">"). Optional arguments
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are listed inside square brackets ("[" and "]"). Each argument is
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followed by its type, so "<key: string>" represents an argument
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called "key" that is a string. Literal strings are represented with
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double-quoted strings. Alternatives are separated with slashes, and
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parenthesis are used for grouping, similar to [ABNF].
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In the "Syntax" line, there are three special pieces of syntax that
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are frequently repeated, MATCH-TYPE, COMPARATOR, and ADDRESS-PART.
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These are discussed in sections 2.7.1, 2.7.3, and 2.7.4,
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respectively.
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The formal grammar for these commands in section 10 and is the
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authoritative reference on how to construct commands, but the formal
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grammar does not specify the order, semantics, number or types of
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arguments to commands, nor the legal command names. The intent is to
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allow for extension without changing the grammar.
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1.2. Example mail messages
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The following mail messages will be used throughout this document in
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examples.
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Message A
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-----------------------------------------------------------
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Date: Tue, 1 Apr 1997 09:06:31 -0800 (PST)
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From: coyote@desert.example.org
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To: roadrunner@acme.example.com
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Subject: I have a present for you
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Look, I'm sorry about the whole anvil thing, and I really
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didn't mean to try and drop it on you from the top of the
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cliff. I want to try to make it up to you. I've got some
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great birdseed over here at my place--top of the line
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Showalter Standards Track [Page 4]
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RFC 3028 Sieve: A Mail Filtering Language January 2001
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stuff--and if you come by, I'll have it all wrapped up
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for you. I'm really sorry for all the problems I've caused
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for you over the years, but I know we can work this out.
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--
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Wile E. Coyote "Super Genius" coyote@desert.example.org
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-----------------------------------------------------------
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Message B
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-----------------------------------------------------------
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From: youcouldberich!@reply-by-postal-mail.invalid
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Sender: b1ff@de.res.example.com
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To: rube@landru.example.edu
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Date: Mon, 31 Mar 1997 18:26:10 -0800
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Subject: $$$ YOU, TOO, CAN BE A MILLIONAIRE! $$$
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YOU MAY HAVE ALREADY WON TEN MILLION DOLLARS, BUT I DOUBT
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IT! SO JUST POST THIS TO SIX HUNDRED NEWSGROUPS! IT WILL
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GUARANTEE THAT YOU GET AT LEAST FIVE RESPONSES WITH MONEY!
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MONEY! MONEY! COLD HARD CASH! YOU WILL RECEIVE OVER
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$20,000 IN LESS THAN TWO MONTHS! AND IT'S LEGAL!!!!!!!!!
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!!!!!!!!!!!!!!!!!!111111111!!!!!!!11111111111!!1 JUST
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SEND $5 IN SMALL, UNMARKED BILLS TO THE ADDRESSES BELOW!
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-----------------------------------------------------------
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2. Design
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2.1. Form of the Language
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The language consists of a set of commands. Each command consists of
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a set of tokens delimited by whitespace. The command identifier is
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the first token and it is followed by zero or more argument tokens.
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Arguments may be literal data, tags, blocks of commands, or test
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commands.
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The language is represented in UTF-8, as specified in [UTF-8].
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Tokens in the ASCII range are considered case-insensitive.
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2.2. Whitespace
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Whitespace is used to separate tokens. Whitespace is made up of
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tabs, newlines (CRLF, never just CR or LF), and the space character.
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The amount of whitespace used is not significant.
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Showalter Standards Track [Page 5]
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RFC 3028 Sieve: A Mail Filtering Language January 2001
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2.3. Comments
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Two types of comments are offered. Comments are semantically
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equivalent to whitespace and can be used anyplace that whitespace is
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(with one exception in multi-line strings, as described in the
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grammar).
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Hash comments begin with a "#" character that is not contained within
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a string and continue until the next CRLF.
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Example: if size :over 100K { # this is a comment
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discard;
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}
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Bracketed comments begin with the token "/*" and end with "*/" outside
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of a string. Bracketed comments may span multiple lines. Bracketed
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comments do not nest.
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Example: if size :over 100K { /* this is a comment
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this is still a comment */ discard /* this is a comment
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*/ ;
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}
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2.4. Literal Data
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Literal data means data that is not executed, merely evaluated "as
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is", to be used as arguments to commands. Literal data is limited to
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numbers and strings.
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2.4.1. Numbers
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Numbers are given as ordinary decimal numbers. However, those
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numbers that have a tendency to be fairly large, such as message
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sizes, MAY have a "K", "M", or "G" appended to indicate a multiple of
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a power of two. To be comparable with the power-of-two-based
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versions of SI units that computers frequently use, K specifies
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kibi-, or 1,024 (2^10) times the value of the number; M specifies
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mebi-, or 1,048,576 (2^20) times the value of the number; and G
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specifies tebi-, or 1,073,741,824 (2^30) times the value of the
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number [BINARY-SI].
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Implementations MUST provide 31 bits of magnitude in numbers, but MAY
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provide more.
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Only positive integers are permitted by this specification.
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Showalter Standards Track [Page 6]
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RFC 3028 Sieve: A Mail Filtering Language January 2001
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2.4.2. Strings
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Scripts involve large numbers of strings as they are used for pattern
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matching, addresses, textual bodies, etc. Typically, short quoted
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strings suffice for most uses, but a more convenient form is provided
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for longer strings such as bodies of messages.
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A quoted string starts and ends with a single double quote (the <">
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character, ASCII 34). A backslash ("\", ASCII 92) inside of a quoted
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string is followed by either another backslash or a double quote.
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This two-character sequence represents a single backslash or double-
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quote within the string, respectively.
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No other characters should be escaped with a single backslash.
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An undefined escape sequence (such as "\a" in a context where "a" has
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no special meaning) is interpreted as if there were no backslash (in
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this case, "\a" is just "a").
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Non-printing characters such as tabs, CR and LF, and control
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characters are permitted in quoted strings. Quoted strings MAY span
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multiple lines. NUL (ASCII 0) is not allowed in strings.
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For entering larger amounts of text, such as an email message, a
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multi-line form is allowed. It starts with the keyword "text:",
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followed by a CRLF, and ends with the sequence of a CRLF, a single
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period, and another CRLF. In order to allow the message to contain
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lines with a single-dot, lines are dot-stuffed. That is, when
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composing a message body, an extra `.' is added before each line
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which begins with a `.'. When the server interprets the script,
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these extra dots are removed. Note that a line that begins with a
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dot followed by a non-dot character is not interpreted dot-stuffed;
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that is, ".foo" is interpreted as ".foo". However, because this is
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potentially ambiguous, scripts SHOULD be properly dot-stuffed so such
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lines do not appear.
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Note that a hashed comment or whitespace may occur in between the
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"text:" and the CRLF, but not within the string itself. Bracketed
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comments are not allowed here.
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2.4.2.1. String Lists
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When matching patterns, it is frequently convenient to match against
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groups of strings instead of single strings. For this reason, a list
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of strings is allowed in many tests, implying that if the test is
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true using any one of the strings, then the test is true.
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Implementations are encouraged to use short-circuit evaluation in
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these cases.
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Showalter Standards Track [Page 7]
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RFC 3028 Sieve: A Mail Filtering Language January 2001
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For instance, the test `header :contains ["To", "Cc"]
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["me@example.com", "me00@landru.example.edu"]' is true if either the
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To header or Cc header of the input message contains either of the
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e-mail addresses "me@example.com" or "me00@landru.example.edu".
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Conversely, in any case where a list of strings is appropriate, a
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single string is allowed without being a member of a list: it is
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equivalent to a list with a single member. This means that the test
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`exists "To"' is equivalent to the test `exists ["To"]'.
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2.4.2.2. Headers
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Headers are a subset of strings. In the Internet Message
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Specification [IMAIL] [RFC1123], each header line is allowed to have
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whitespace nearly anywhere in the line, including after the field
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name and before the subsequent colon. Extra spaces between the
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header name and the ":" in a header field are ignored.
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A header name never contains a colon. The "From" header refers to a
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line beginning "From:" (or "From :", etc.). No header will match
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the string "From:" due to the trailing colon.
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Folding of long header lines (as described in [IMAIL] 3.4.8) is
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removed prior to interpretation of the data. The folding syntax (the
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CRLF that ends a line plus any leading whitespace at the beginning of
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the next line that indicates folding) are interpreted as if they were
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a single space.
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2.4.2.3. Addresses
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A number of commands call for email addresses, which are also a
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subset of strings. When these addresses are used in outbound
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contexts, addresses must be compliant with [IMAIL], but are further
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constrained. Using the symbols defined in [IMAIL], section 6.1, the
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syntax of an address is:
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sieve-address = addr-spec ; simple address
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/ phrase "<" addr-spec ">" ; name & addr-spec
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That is, routes and group syntax are not permitted. If multiple
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addresses are required, use a string list. Named groups are not used
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here.
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Implementations MUST ensure that the addresses are syntactically
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valid, but need not ensure that they actually identify an email
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recipient.
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Showalter Standards Track [Page 8]
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RFC 3028 Sieve: A Mail Filtering Language January 2001
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2.4.2.4. MIME Parts
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In a few places, [MIME] body parts are represented as strings. These
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parts include MIME headers and the body. This provides a way of
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embedding typed data within a Sieve script so that, among other
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things, character sets other than UTF-8 can be used for output
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messages.
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2.5. Tests
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Tests are given as arguments to commands in order to control their
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actions. In this document, tests are given to if/elsif/else to
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decide which block of code is run.
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Tests MUST NOT have side effects. That is, a test cannot affect the
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state of the filter or message. No tests in this specification have
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side effects, and side effects are forbidden in extension tests as
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well.
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The rationale for this is that tests with side effects impair
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readability and maintainability and are difficult to represent in a
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graphic interface for generating scripts. Side effects are confined
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to actions where they are clearer.
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2.5.1. Test Lists
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Some tests ("allof" and "anyof", which implement logical "and" and
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logical "or", respectively) may require more than a single test as an
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argument. The test-list syntax element provides a way of grouping
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tests.
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Example: if anyof (not exists ["From", "Date"],
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header :contains "from" "fool@example.edu") {
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discard;
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}
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2.6. Arguments
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In order to specify what to do, most commands take arguments. There
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are three types of arguments: positional, tagged, and optional.
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2.6.1. Positional Arguments
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Positional arguments are given to a command which discerns their
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meaning based on their order. When a command takes positional
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arguments, all positional arguments must be supplied and must be in
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the order prescribed.
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Showalter Standards Track [Page 9]
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RFC 3028 Sieve: A Mail Filtering Language January 2001
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|
||
2.6.2. Tagged Arguments
|
||
|
||
This document provides for tagged arguments in the style of
|
||
CommonLISP. These are also similar to flags given to commands in
|
||
most command-line systems.
|
||
|
||
A tagged argument is an argument for a command that begins with ":"
|
||
followed by a tag naming the argument, such as ":contains". This
|
||
argument means that zero or more of the next tokens have some
|
||
particular meaning depending on the argument. These next tokens may
|
||
be numbers or strings but they are never blocks.
|
||
|
||
Tagged arguments are similar to positional arguments, except that
|
||
instead of the meaning being derived from the command, it is derived
|
||
from the tag.
|
||
|
||
Tagged arguments must appear before positional arguments, but they
|
||
may appear in any order with other tagged arguments. For simplicity
|
||
of the specification, this is not expressed in the syntax definitions
|
||
with commands, but they still may be reordered arbitrarily provided
|
||
they appear before positional arguments. Tagged arguments may be
|
||
mixed with optional arguments.
|
||
|
||
To simplify this specification, tagged arguments SHOULD NOT take
|
||
tagged arguments as arguments.
|
||
|
||
2.6.3. Optional Arguments
|
||
|
||
Optional arguments are exactly like tagged arguments except that they
|
||
may be left out, in which case a default value is implied. Because
|
||
optional arguments tend to result in shorter scripts, they have been
|
||
used far more than tagged arguments.
|
||
|
||
One particularly noteworthy case is the ":comparator" argument, which
|
||
allows the user to specify which [ACAP] comparator will be used to
|
||
compare two strings, since different languages may impose different
|
||
orderings on UTF-8 [UTF-8] characters.
|
||
|
||
2.6.4. Types of Arguments
|
||
|
||
Abstractly, arguments may be literal data, tests, or blocks of
|
||
commands. In this way, an "if" control structure is merely a command
|
||
that happens to take a test and a block as arguments and may execute
|
||
the block of code.
|
||
|
||
However, this abstraction is ambiguous from a parsing standpoint.
|
||
The grammar in section 9.2 presents a parsable version of this:
|
||
Arguments are string-lists, numbers, and tags, which may be followed
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 10]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
by a test or a test-list, which may be followed by a block of
|
||
commands. No more than one test or test list, nor more than one
|
||
block of commands, may be used, and commands that end with blocks of
|
||
commands do not end with semicolons.
|
||
|
||
2.7. String Comparison
|
||
|
||
When matching one string against another, there are a number of ways
|
||
of performing the match operation. These are accomplished with three
|
||
types of matches: an exact match, a substring match, and a wildcard
|
||
glob-style match. These are described below.
|
||
|
||
In order to provide for matches between character sets and case
|
||
insensitivity, Sieve borrows ACAP's comparator registry.
|
||
|
||
However, when a string represents the name of a header, the
|
||
comparator is never user-specified. Header comparisons are always
|
||
done with the "i;ascii-casemap" operator, i.e., case-insensitive
|
||
comparisons, because this is the way things are defined in the
|
||
message specification [IMAIL].
|
||
|
||
2.7.1. Match Type
|
||
|
||
There are three match types describing the matching used in this
|
||
specification: ":is", ":contains", and ":matches". Match type
|
||
arguments are supplied to those commands which allow them to specify
|
||
what kind of match is to be performed.
|
||
|
||
These are used as tagged arguments to tests that perform string
|
||
comparison.
|
||
|
||
The ":contains" match type describes a substring match. If the value
|
||
argument contains the key argument as a substring, the match is true.
|
||
For instance, the string "frobnitzm" contains "frob" and "nit", but
|
||
not "fbm". The null key ("") is contained in all values.
|
||
|
||
The ":is" match type describes an absolute match; if the contents of
|
||
the first string are absolutely the same as the contents of the
|
||
second string, they match. Only the string "frobnitzm" is the string
|
||
"frobnitzm". The null key ":is" and only ":is" the null value.
|
||
|
||
The ":matches" version specifies a wildcard match using the
|
||
characters "*" and "?". "*" matches zero or more characters, and "?"
|
||
matches a single character. "?" and "*" may be escaped as "\\?" and
|
||
"\\*" in strings to match against themselves. The first backslash
|
||
escapes the second backslash; together, they escape the "*". This is
|
||
awkward, but it is commonplace in several programming languages that
|
||
use globs and regular expressions.
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 11]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
In order to specify what type of match is supposed to happen,
|
||
commands that support matching take optional tagged arguments
|
||
":matches", ":is", and ":contains". Commands default to using ":is"
|
||
matching if no match type argument is supplied. Note that these
|
||
modifiers may interact with comparators; in particular, some
|
||
comparators are not suitable for matching with ":contains" or
|
||
":matches". It is an error to use a comparator with ":contains" or
|
||
":matches" that is not compatible with it.
|
||
|
||
It is an error to give more than one of these arguments to a given
|
||
command.
|
||
|
||
For convenience, the "MATCH-TYPE" syntax element is defined here as
|
||
follows:
|
||
|
||
Syntax: ":is" / ":contains" / ":matches"
|
||
|
||
2.7.2. Comparisons Across Character Sets
|
||
|
||
All Sieve scripts are represented in UTF-8, but messages may involve
|
||
a number of character sets. In order for comparisons to work across
|
||
character sets, implementations SHOULD implement the following
|
||
behavior:
|
||
|
||
Implementations decode header charsets to UTF-8. Two strings are
|
||
considered equal if their UTF-8 representations are identical.
|
||
Implementations should decode charsets represented in the forms
|
||
specified by [MIME] for both message headers and bodies.
|
||
Implementations must be capable of decoding US-ASCII, ISO-8859-1,
|
||
the ASCII subset of ISO-8859-* character sets, and UTF-8.
|
||
|
||
If implementations fail to support the above behavior, they MUST
|
||
conform to the following:
|
||
|
||
No two strings can be considered equal if one contains octets
|
||
greater than 127.
|
||
|
||
2.7.3. Comparators
|
||
|
||
In order to allow for language-independent, case-independent matches,
|
||
the match type may be coupled with a comparator name. Comparators
|
||
are described for [ACAP]; a registry is defined for ACAP, and this
|
||
specification uses that registry.
|
||
|
||
ACAP defines multiple comparator types. Only equality types are used
|
||
in this specification.
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 12]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
All implementations MUST support the "i;octet" comparator (simply
|
||
compares octets) and the "i;ascii-casemap" comparator (which treats
|
||
uppercase and lowercase characters in the ASCII subset of UTF-8 as
|
||
the same). If left unspecified, the default is "i;ascii-casemap".
|
||
|
||
Some comparators may not be usable with substring matches; that is,
|
||
they may only work with ":is". It is an error to try and use a
|
||
comparator with ":matches" or ":contains" that is not compatible with
|
||
it.
|
||
|
||
A comparator is specified by the ":comparator" option with commands
|
||
that support matching. This option is followed by a string providing
|
||
the name of the comparator to be used. For convenience, the syntax
|
||
of a comparator is abbreviated to "COMPARATOR", and (repeated in
|
||
several tests) is as follows:
|
||
|
||
Syntax: ":comparator" <comparator-name: string>
|
||
|
||
So in this example,
|
||
|
||
Example: if header :contains :comparator "i;octet" "Subject"
|
||
"MAKE MONEY FAST" {
|
||
discard;
|
||
}
|
||
|
||
would discard any message with subjects like "You can MAKE MONEY
|
||
FAST", but not "You can Make Money Fast", since the comparator used
|
||
is case-sensitive.
|
||
|
||
Comparators other than i;octet and i;ascii-casemap must be declared
|
||
with require, as they are extensions. If a comparator declared with
|
||
require is not known, it is an error, and execution fails. If the
|
||
comparator is not declared with require, it is also an error, even if
|
||
the comparator is supported. (See 2.10.5.)
|
||
|
||
Both ":matches" and ":contains" match types are compatible with the
|
||
"i;octet" and "i;ascii-casemap" comparators and may be used with
|
||
them.
|
||
|
||
It is an error to give more than one of these arguments to a given
|
||
command.
|
||
|
||
2.7.4. Comparisons Against Addresses
|
||
|
||
Addresses are one of the most frequent things represented as strings.
|
||
These are structured, and being able to compare against the local-
|
||
part or the domain of an address is useful, so some tests that act
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 13]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
exclusively on addresses take an additional optional argument that
|
||
specifies what the test acts on.
|
||
|
||
These optional arguments are ":localpart", ":domain", and ":all",
|
||
which act on the local-part (left-side), the domain part (right-
|
||
side), and the whole address.
|
||
|
||
The kind of comparison done, such as whether or not the test done is
|
||
case-insensitive, is specified as a comparator argument to the test.
|
||
|
||
If an optional address-part is omitted, the default is ":all".
|
||
|
||
It is an error to give more than one of these arguments to a given
|
||
command.
|
||
|
||
For convenience, the "ADDRESS-PART" syntax element is defined here as
|
||
follows:
|
||
|
||
Syntax: ":localpart" / ":domain" / ":all"
|
||
|
||
2.8. Blocks
|
||
|
||
Blocks are sets of commands enclosed within curly braces. Blocks are
|
||
supplied to commands so that the commands can implement control
|
||
commands.
|
||
|
||
A control structure is a command that happens to take a test and a
|
||
block as one of its arguments; depending on the result of the test
|
||
supplied as another argument, it runs the code in the block some
|
||
number of times.
|
||
|
||
With the commands supplied in this memo, there are no loops. The
|
||
control structures supplied--if, elsif, and else--run a block either
|
||
once or not at all. So there are two arguments, the test and the
|
||
block.
|
||
|
||
2.9. Commands
|
||
|
||
Sieve scripts are sequences of commands. Commands can take any of
|
||
the tokens above as arguments, and arguments may be either tagged or
|
||
positional arguments. Not all commands take all arguments.
|
||
|
||
There are three kinds of commands: test commands, action commands,
|
||
and control commands.
|
||
|
||
The simplest is an action command. An action command is an
|
||
identifier followed by zero or more arguments, terminated by a
|
||
semicolon. Action commands do not take tests or blocks as arguments.
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 14]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
A control command is similar, but it takes a test as an argument, and
|
||
ends with a block instead of a semicolon.
|
||
|
||
A test command is used as part of a control command. It is used to
|
||
specify whether or not the block of code given to the control command
|
||
is executed.
|
||
|
||
2.10. Evaluation
|
||
|
||
2.10.1. Action Interaction
|
||
|
||
Some actions cannot be used with other actions because the result
|
||
would be absurd. These restrictions are noted throughout this memo.
|
||
|
||
Extension actions MUST state how they interact with actions defined
|
||
in this specification.
|
||
|
||
2.10.2. Implicit Keep
|
||
|
||
Previous experience with filtering systems suggests that cases tend
|
||
to be missed in scripts. To prevent errors, Sieve has an "implicit
|
||
keep".
|
||
|
||
An implicit keep is a keep action (see 4.4) performed in absence of
|
||
any action that cancels the implicit keep.
|
||
|
||
An implicit keep is performed if a message is not written to a
|
||
mailbox, redirected to a new address, or explicitly thrown out. That
|
||
is, if a fileinto, a keep, a redirect, or a discard is performed, an
|
||
implicit keep is not.
|
||
|
||
Some actions may be defined to not cancel the implicit keep. These
|
||
actions may not directly affect the delivery of a message, and are
|
||
used for their side effects. None of the actions specified in this
|
||
document meet that criteria, but extension actions will.
|
||
|
||
For instance, with any of the short messages offered above, the
|
||
following script produces no actions.
|
||
|
||
Example: if size :over 500K { discard; }
|
||
|
||
As a result, the implicit keep is taken.
|
||
|
||
2.10.3. Message Uniqueness in a Mailbox
|
||
|
||
Implementations SHOULD NOT deliver a message to the same folder more
|
||
than once, even if a script explicitly asks for a message to be
|
||
written to a mailbox twice.
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 15]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
The test for equality of two messages is implementation-defined.
|
||
|
||
If a script asks for a message to be written to a mailbox twice, it
|
||
MUST NOT be treated as an error.
|
||
|
||
2.10.4. Limits on Numbers of Actions
|
||
|
||
Site policy MAY limit numbers of actions taken and MAY impose
|
||
restrictions on which actions can be used together. In the event
|
||
that a script hits a policy limit on the number of actions taken for
|
||
a particular message, an error occurs.
|
||
|
||
Implementations MUST prohibit more than one reject.
|
||
|
||
Implementations MUST allow at least one keep or one fileinto. If
|
||
fileinto is not implemented, implementations MUST allow at least one
|
||
keep.
|
||
|
||
Implementations SHOULD prohibit reject when used with other actions.
|
||
|
||
2.10.5. Extensions and Optional Features
|
||
|
||
Because of the differing capabilities of many mail systems, several
|
||
features of this specification are optional. Before any of these
|
||
extensions can be executed, they must be declared with the "require"
|
||
action.
|
||
|
||
If an extension is not enabled with "require", implementations MUST
|
||
treat it as if they did not support it at all.
|
||
|
||
If a script does not understand an extension declared with require,
|
||
the script must not be used at all. Implementations MUST NOT execute
|
||
scripts which require unknown capability names.
|
||
|
||
Note: The reason for this restriction is that prior experiences with
|
||
languages such as LISP and Tcl suggest that this is a workable
|
||
way of noting that a given script uses an extension.
|
||
|
||
Experience with PostScript suggests that mechanisms that allow
|
||
a script to work around missing extensions are not used in
|
||
practice.
|
||
|
||
Extensions which define actions MUST state how they interact with
|
||
actions discussed in the base specification.
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 16]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
2.10.6. Errors
|
||
|
||
In any programming language, there are compile-time and run-time
|
||
errors.
|
||
|
||
Compile-time errors are ones in syntax that are detectable if a
|
||
syntax check is done.
|
||
|
||
Run-time errors are not detectable until the script is run. This
|
||
includes transient failures like disk full conditions, but also
|
||
includes issues like invalid combinations of actions.
|
||
|
||
When an error occurs in a Sieve script, all processing stops.
|
||
|
||
Implementations MAY choose to do a full parse, then evaluate the
|
||
script, then do all actions. Implementations might even go so far as
|
||
to ensure that execution is atomic (either all actions are executed
|
||
or none are executed).
|
||
|
||
Other implementations may choose to parse and run at the same time.
|
||
Such implementations are simpler, but have issues with partial
|
||
failure (some actions happen, others don't).
|
||
|
||
Implementations might even go so far as to ensure that scripts can
|
||
never execute an invalid set of actions (e.g., reject + fileinto)
|
||
before execution, although this could involve solving the Halting
|
||
Problem.
|
||
|
||
This specification allows any of these approaches. Solving the
|
||
Halting Problem is considered extra credit.
|
||
|
||
When an error happens, implementations MUST notify the user that an
|
||
error occurred, which actions (if any) were taken, and do an implicit
|
||
keep.
|
||
|
||
2.10.7. Limits on Execution
|
||
|
||
Implementations may limit certain constructs. However, this
|
||
specification places a lower bound on some of these limits.
|
||
|
||
Implementations MUST support fifteen levels of nested blocks.
|
||
|
||
Implementations MUST support fifteen levels of nested test lists.
|
||
|
||
3. Control Commands
|
||
|
||
Control structures are needed to allow for multiple and conditional
|
||
actions.
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 17]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
3.1. Control Structure If
|
||
|
||
There are three pieces to if: "if", "elsif", and "else". Each is
|
||
actually a separate command in terms of the grammar. However, an
|
||
elsif MUST only follow an if, and an else MUST follow only either an
|
||
if or an elsif. An error occurs if these conditions are not met.
|
||
|
||
Syntax: if <test1: test> <block1: block>
|
||
|
||
Syntax: elsif <test2: test> <block2: block>
|
||
|
||
Syntax: else <block>
|
||
|
||
The semantics are similar to those of any of the many other
|
||
programming languages these control commands appear in. When the
|
||
interpreter sees an "if", it evaluates the test associated with it.
|
||
If the test is true, it executes the block associated with it.
|
||
|
||
If the test of the "if" is false, it evaluates the test of the first
|
||
"elsif" (if any). If the test of "elsif" is true, it runs the
|
||
elsif's block. An elsif may be followed by an elsif, in which case,
|
||
the interpreter repeats this process until it runs out of elsifs.
|
||
|
||
When the interpreter runs out of elsifs, there may be an "else" case.
|
||
If there is, and none of the if or elsif tests were true, the
|
||
interpreter runs the else case.
|
||
|
||
This provides a way of performing exactly one of the blocks in the
|
||
chain.
|
||
|
||
In the following example, both Message A and B are dropped.
|
||
|
||
Example: require "fileinto";
|
||
if header :contains "from" "coyote" {
|
||
discard;
|
||
} elsif header :contains ["subject"] ["$$$"] {
|
||
discard;
|
||
} else {
|
||
fileinto "INBOX";
|
||
}
|
||
|
||
|
||
When the script below is run over message A, it redirects the message
|
||
to acm@example.edu; message B, to postmaster@example.edu; any other
|
||
message is redirected to field@example.edu.
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 18]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
Example: if header :contains ["From"] ["coyote"] {
|
||
redirect "acm@example.edu";
|
||
} elsif header :contains "Subject" "$$$" {
|
||
redirect "postmaster@example.edu";
|
||
} else {
|
||
redirect "field@example.edu";
|
||
}
|
||
|
||
Note that this definition prohibits the "... else if ..." sequence
|
||
used by C. This is intentional, because this construct produces a
|
||
shift-reduce conflict.
|
||
|
||
3.2. Control Structure Require
|
||
|
||
Syntax: require <capabilities: string-list>
|
||
|
||
The require action notes that a script makes use of a certain
|
||
extension. Such a declaration is required to use the extension, as
|
||
discussed in section 2.10.5. Multiple capabilities can be declared
|
||
with a single require.
|
||
|
||
The require command, if present, MUST be used before anything other
|
||
than a require can be used. An error occurs if a require appears
|
||
after a command other than require.
|
||
|
||
Example: require ["fileinto", "reject"];
|
||
|
||
Example: require "fileinto";
|
||
require "vacation";
|
||
|
||
3.3. Control Structure Stop
|
||
|
||
Syntax: stop
|
||
|
||
The "stop" action ends all processing. If no actions have been
|
||
executed, then the keep action is taken.
|
||
|
||
4. Action Commands
|
||
|
||
This document supplies five actions that may be taken on a message:
|
||
keep, fileinto, redirect, reject, and discard.
|
||
|
||
Implementations MUST support the "keep", "discard", and "redirect"
|
||
actions.
|
||
|
||
Implementations SHOULD support "reject" and "fileinto".
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 19]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
Implementations MAY limit the number of certain actions taken (see
|
||
section 2.10.4).
|
||
|
||
4.1. Action reject
|
||
|
||
Syntax: reject <reason: string>
|
||
|
||
The optional "reject" action refuses delivery of a message by sending
|
||
back an [MDN] to the sender. It resends the message to the sender,
|
||
wrapping it in a "reject" form, noting that it was rejected by the
|
||
recipient. In the following script, message A is rejected and
|
||
returned to the sender.
|
||
|
||
Example: if header :contains "from" "coyote@desert.example.org" {
|
||
reject "I am not taking mail from you, and I don't want
|
||
your birdseed, either!";
|
||
}
|
||
|
||
A reject message MUST take the form of a failure MDN as specified by
|
||
[MDN]. The human-readable portion of the message, the first
|
||
component of the MDN, contains the human readable message describing
|
||
the error, and it SHOULD contain additional text alerting the
|
||
original sender that mail was refused by a filter. This part of the
|
||
MDN might appear as follows:
|
||
|
||
------------------------------------------------------------
|
||
Message was refused by recipient's mail filtering program. Reason
|
||
given was as follows:
|
||
|
||
I am not taking mail from you, and I don't want your birdseed,
|
||
either!
|
||
------------------------------------------------------------
|
||
|
||
The MDN action-value field as defined in the MDN specification MUST
|
||
be "deleted" and MUST have the MDN-sent-automatically and automatic-
|
||
action modes set.
|
||
|
||
Because some implementations can not or will not implement the reject
|
||
command, it is optional. The capability string to be used with the
|
||
require command is "reject".
|
||
|
||
4.2. Action fileinto
|
||
|
||
Syntax: fileinto <folder: string>
|
||
|
||
The "fileinto" action delivers the message into the specified folder.
|
||
Implementations SHOULD support fileinto, but in some environments
|
||
this may be impossible.
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 20]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
The capability string for use with the require command is "fileinto".
|
||
|
||
In the following script, message A is filed into folder
|
||
"INBOX.harassment".
|
||
|
||
Example: require "fileinto";
|
||
if header :contains ["from"] "coyote" {
|
||
fileinto "INBOX.harassment";
|
||
}
|
||
|
||
4.3. Action redirect
|
||
|
||
Syntax: redirect <address: string>
|
||
|
||
The "redirect" action is used to send the message to another user at
|
||
a supplied address, as a mail forwarding feature does. The
|
||
"redirect" action makes no changes to the message body or existing
|
||
headers, but it may add new headers. The "redirect" modifies the
|
||
envelope recipient.
|
||
|
||
The redirect command performs an MTA-style "forward"--that is, what
|
||
you get from a .forward file using sendmail under UNIX. The address
|
||
on the SMTP envelope is replaced with the one on the redirect command
|
||
and the message is sent back out. (This is not an MUA-style forward,
|
||
which creates a new message with a different sender and message ID,
|
||
wrapping the old message in a new one.)
|
||
|
||
A simple script can be used for redirecting all mail:
|
||
|
||
Example: redirect "bart@example.edu";
|
||
|
||
Implementations SHOULD take measures to implement loop control,
|
||
possibly including adding headers to the message or counting received
|
||
headers. If an implementation detects a loop, it causes an error.
|
||
|
||
4.4. Action keep
|
||
|
||
Syntax: keep
|
||
|
||
The "keep" action is whatever action is taken in lieu of all other
|
||
actions, if no filtering happens at all; generally, this simply means
|
||
to file the message into the user's main mailbox. This command
|
||
provides a way to execute this action without needing to know the
|
||
name of the user's main mailbox, providing a way to call it without
|
||
needing to understand the user's setup, or the underlying mail
|
||
system.
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 21]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
For instance, in an implementation where the IMAP server is running
|
||
scripts on behalf of the user at time of delivery, a keep command is
|
||
equivalent to a fileinto "INBOX".
|
||
|
||
Example: if size :under 1M { keep; } else { discard; }
|
||
|
||
Note that the above script is identical to the one below.
|
||
|
||
Example: if not size :under 1M { discard; }
|
||
|
||
4.5. Action discard
|
||
|
||
Syntax: discard
|
||
|
||
Discard is used to silently throw away the message. It does so by
|
||
simply canceling the implicit keep. If discard is used with other
|
||
actions, the other actions still happen. Discard is compatible with
|
||
all other actions. (For instance fileinto+discard is equivalent to
|
||
fileinto.)
|
||
|
||
Discard MUST be silent; that is, it MUST NOT return a non-delivery
|
||
notification of any kind ([DSN], [MDN], or otherwise).
|
||
|
||
In the following script, any mail from "idiot@example.edu" is thrown
|
||
out.
|
||
|
||
Example: if header :contains ["from"] ["idiot@example.edu"] {
|
||
discard;
|
||
}
|
||
|
||
While an important part of this language, "discard" has the potential
|
||
to create serious problems for users: Students who leave themselves
|
||
logged in to an unattended machine in a public computer lab may find
|
||
their script changed to just "discard". In order to protect users in
|
||
this situation (along with similar situations), implementations MAY
|
||
keep messages destroyed by a script for an indefinite period, and MAY
|
||
disallow scripts that throw out all mail.
|
||
|
||
5. Test Commands
|
||
|
||
Tests are used in conditionals to decide which part(s) of the
|
||
conditional to execute.
|
||
|
||
Implementations MUST support these tests: "address", "allof",
|
||
"anyof", "exists", "false", "header", "not", "size", and "true".
|
||
|
||
Implementations SHOULD support the "envelope" test.
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 22]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
5.1. Test address
|
||
|
||
Syntax: address [ADDRESS-PART] [COMPARATOR] [MATCH-TYPE]
|
||
<header-list: string-list> <key-list: string-list>
|
||
|
||
The address test matches Internet addresses in structured headers
|
||
that contain addresses. It returns true if any header contains any
|
||
key in the specified part of the address, as modified by the
|
||
comparator and the match keyword.
|
||
|
||
Like envelope and header, this test returns true if any combination
|
||
of the header-list and key-list arguments match.
|
||
|
||
Internet email addresses [IMAIL] have the somewhat awkward
|
||
characteristic that the local-part to the left of the at-sign is
|
||
considered case sensitive, and the domain-part to the right of the
|
||
at-sign is case insensitive. The "address" command does not deal
|
||
with this itself, but provides the ADDRESS-PART argument for allowing
|
||
users to deal with it.
|
||
|
||
The address primitive never acts on the phrase part of an email
|
||
address, nor on comments within that address. It also never acts on
|
||
group names, although it does act on the addresses within the group
|
||
construct.
|
||
|
||
Implementations MUST restrict the address test to headers that
|
||
contain addresses, but MUST include at least From, To, Cc, Bcc,
|
||
Sender, Resent-From, Resent-To, and SHOULD include any other header
|
||
that utilizes an "address-list" structured header body.
|
||
|
||
Example: if address :is :all "from" "tim@example.com" {
|
||
discard;
|
||
|
||
5.2. Test allof
|
||
|
||
Syntax: allof <tests: test-list>
|
||
|
||
The allof test performs a logical AND on the tests supplied to it.
|
||
|
||
Example: allof (false, false) => false
|
||
allof (false, true) => false
|
||
allof (true, true) => true
|
||
|
||
The allof test takes as its argument a test-list.
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 23]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
5.3. Test anyof
|
||
|
||
Syntax: anyof <tests: test-list>
|
||
|
||
The anyof test performs a logical OR on the tests supplied to it.
|
||
|
||
Example: anyof (false, false) => false
|
||
anyof (false, true) => true
|
||
anyof (true, true) => true
|
||
|
||
5.4. Test envelope
|
||
|
||
Syntax: envelope [COMPARATOR] [ADDRESS-PART] [MATCH-TYPE]
|
||
<envelope-part: string-list> <key-list: string-list>
|
||
|
||
The "envelope" test is true if the specified part of the SMTP (or
|
||
equivalent) envelope matches the specified key.
|
||
|
||
If one of the envelope-part strings is (case insensitive) "from",
|
||
then matching occurs against the FROM address used in the SMTP MAIL
|
||
command.
|
||
|
||
If one of the envelope-part strings is (case insensitive) "to", then
|
||
matching occurs against the TO address used in the SMTP RCPT command
|
||
that resulted in this message getting delivered to this user. Note
|
||
that only the most recent TO is available, and only the one relevant
|
||
to this user.
|
||
|
||
The envelope-part is a string list and may contain more than one
|
||
parameter, in which case all of the strings specified in the key-list
|
||
are matched against all parts given in the envelope-part list.
|
||
|
||
Like address and header, this test returns true if any combination of
|
||
the envelope-part and key-list arguments is true.
|
||
|
||
All tests against envelopes MUST drop source routes.
|
||
|
||
If the SMTP transaction involved several RCPT commands, only the data
|
||
from the RCPT command that caused delivery to this user is available
|
||
in the "to" part of the envelope.
|
||
|
||
If a protocol other than SMTP is used for message transport,
|
||
implementations are expected to adapt this command appropriately.
|
||
|
||
The envelope command is optional. Implementations SHOULD support it,
|
||
but the necessary information may not be available in all cases.
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 24]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
Example: require "envelope";
|
||
if envelope :all :is "from" "tim@example.com" {
|
||
discard;
|
||
}
|
||
|
||
5.5. Test exists
|
||
|
||
Syntax: exists <header-names: string-list>
|
||
|
||
The "exists" test is true if the headers listed in the header-names
|
||
argument exist within the message. All of the headers must exist or
|
||
the test is false.
|
||
|
||
The following example throws out mail that doesn't have a From header
|
||
and a Date header.
|
||
|
||
Example: if not exists ["From","Date"] {
|
||
discard;
|
||
}
|
||
|
||
5.6. Test false
|
||
|
||
Syntax: false
|
||
|
||
The "false" test always evaluates to false.
|
||
|
||
5.7. Test header
|
||
|
||
Syntax: header [COMPARATOR] [MATCH-TYPE]
|
||
<header-names: string-list> <key-list: string-list>
|
||
|
||
The "header" test evaluates to true if any header name matches any
|
||
key. The type of match is specified by the optional match argument,
|
||
which defaults to ":is" if not specified, as specified in section
|
||
2.6.
|
||
|
||
Like address and envelope, this test returns true if any combination
|
||
of the string-list and key-list arguments match.
|
||
|
||
If a 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 header
|
||
|
||
X-Caffeine: C8H10N4O2
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 25]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
these tests on that header evaluate as follows:
|
||
|
||
header :is ["X-Caffeine"] [""] => false
|
||
header :contains ["X-Caffeine"] [""] => true
|
||
|
||
5.8. Test not
|
||
|
||
Syntax: not <test>
|
||
|
||
The "not" test takes some other test as an argument, and yields the
|
||
opposite result. "not false" evaluates to "true" and "not true"
|
||
evaluates to "false".
|
||
|
||
5.9. Test size
|
||
|
||
Syntax: size <":over" / ":under"> <limit: number>
|
||
|
||
The "size" test deals with the size of a message. It takes either a
|
||
tagged argument of ":over" or ":under", followed by a number
|
||
representing the size of the message.
|
||
|
||
If the argument is ":over", and the size of the message is greater
|
||
than the number provided, the test is true; otherwise, it is false.
|
||
|
||
If the argument is ":under", and the size of the message is less than
|
||
the number provided, the test is true; otherwise, it is false.
|
||
|
||
Exactly one of ":over" or ":under" must be specified, and anything
|
||
else is an error.
|
||
|
||
The size of a message is defined to be the number of octets from the
|
||
initial header until the last character in the message body.
|
||
|
||
Note that for a message that is exactly 4,000 octets, the message is
|
||
neither ":over" 4000 octets or ":under" 4000 octets.
|
||
|
||
5.10. Test true
|
||
|
||
Syntax: true
|
||
|
||
The "true" test always evaluates to true.
|
||
|
||
6. Extensibility
|
||
|
||
New control structures, actions, and tests can be added to the
|
||
language. Sites must make these features known to their users; this
|
||
document does not define a way to discover the list of extensions
|
||
supported by the server.
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 26]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
Any extensions to this language MUST define a capability string that
|
||
uniquely identifies that extension. If a new version of an extension
|
||
changes the functionality of a previously defined extension, it MUST
|
||
use a different name.
|
||
|
||
In a situation where there is a submission protocol and an extension
|
||
advertisement mechanism aware of the details of this language,
|
||
scripts submitted can be checked against the mail server to prevent
|
||
use of an extension that the server does not support.
|
||
|
||
Extensions MUST state how they interact with constraints defined in
|
||
section 2.10, e.g., whether they cancel the implicit keep, and which
|
||
actions they are compatible and incompatible with.
|
||
|
||
6.1. Capability String
|
||
|
||
Capability strings are typically short strings describing what
|
||
capabilities are supported by the server.
|
||
|
||
Capability strings 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. Extensions starting with "vnd." SHOULD be followed by the
|
||
name of the vendor and product, such as "vnd.acme.rocket-sled".
|
||
|
||
The following capability strings are defined by this document:
|
||
|
||
envelope The string "envelope" indicates that the implementation
|
||
supports the "envelope" command.
|
||
|
||
fileinto The string "fileinto" indicates that the implementation
|
||
supports the "fileinto" command.
|
||
|
||
reject The string "reject" indicates that the implementation
|
||
supports the "reject" command.
|
||
|
||
comparator- The string "comparator-elbonia" is provided if the
|
||
implementation supports the "elbonia" comparator.
|
||
Therefore, all implementations have at least the
|
||
"comparator-i;octet" and "comparator-i;ascii-casemap"
|
||
capabilities. However, these comparators may be used
|
||
without being declared with require.
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 27]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
6.2. IANA Considerations
|
||
|
||
In order to provide a standard set of extensions, a registry is
|
||
provided by IANA. Capability 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.
|
||
|
||
6.2.1. Template for Capability Registrations
|
||
|
||
The following template is to be used for registering new Sieve
|
||
extensions with IANA.
|
||
|
||
To: iana@iana.org
|
||
Subject: Registration of new Sieve extension
|
||
|
||
Capability name:
|
||
Capability keyword:
|
||
Capability arguments:
|
||
Standards Track/IESG-approved experimental RFC number:
|
||
Person and email address to contact for further information:
|
||
|
||
6.2.2. Initial Capability Registrations
|
||
|
||
The following are to be added to the IANA registry for Sieve
|
||
extensions as the initial contents of the capability registry.
|
||
|
||
Capability name: fileinto
|
||
Capability keyword: fileinto
|
||
Capability arguments: fileinto <folder: string>
|
||
Standards Track/IESG-approved experimental RFC number:
|
||
RFC 3028 (Sieve base spec)
|
||
Person and email address to contact for further information:
|
||
Tim Showalter
|
||
tjs@mirapoint.com
|
||
|
||
Capability name: reject
|
||
Capability keyword: reject
|
||
Capability arguments: reject <reason: string>
|
||
Standards Track/IESG-approved experimental RFC number:
|
||
RFC 3028 (Sieve base spec)
|
||
Person and email address to contact for further information:
|
||
Tim Showalter
|
||
tjs@mirapoint.com
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 28]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
Capability name: envelope
|
||
Capability keyword: envelope
|
||
Capability arguments:
|
||
envelope [COMPARATOR] [ADDRESS-PART] [MATCH-TYPE]
|
||
<envelope-part: string-list> <key-list: string-list>
|
||
Standards Track/IESG-approved experimental RFC number:
|
||
RFC 3028 (Sieve base spec)
|
||
Person and email address to contact for further information:
|
||
Tim Showalter
|
||
tjs@mirapoint.com
|
||
|
||
Capability name: comparator-*
|
||
Capability keyword:
|
||
comparator-* (anything starting with "comparator-")
|
||
Capability arguments: (none)
|
||
Standards Track/IESG-approved experimental RFC number:
|
||
RFC 3028, Sieve, by reference of
|
||
RFC 2244, Application Configuration Access Protocol
|
||
Person and email address to contact for further information:
|
||
Tim Showalter
|
||
tjs@mirapoint.com
|
||
|
||
6.3. Capability Transport
|
||
|
||
As the range of mail systems that this document is intended to apply
|
||
to is quite varied, a method of advertising which capabilities an
|
||
implementation supports is difficult due to the wide range of
|
||
possible implementations. Such a mechanism, however, should have
|
||
property that the implementation can advertise the complete set of
|
||
extensions that it supports.
|
||
|
||
7. Transmission
|
||
|
||
The MIME type for a Sieve script is "application/sieve".
|
||
|
||
The registration of this type for RFC 2048 requirements is as
|
||
follows:
|
||
|
||
Subject: Registration of MIME media type application/sieve
|
||
|
||
MIME media type name: application
|
||
MIME subtype name: sieve
|
||
Required parameters: none
|
||
Optional parameters: none
|
||
Encoding considerations: Most sieve scripts will be textual,
|
||
written in UTF-8. When non-7bit characters are used,
|
||
quoted-printable is appropriate for transport systems
|
||
that require 7bit encoding.
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 29]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
Security considerations: Discussed in section 10 of RFC 3028.
|
||
Interoperability considerations: Discussed in section 2.10.5
|
||
of RFC 3028.
|
||
Published specification: RFC 3028.
|
||
Applications which use this media type: sieve-enabled mail servers
|
||
Additional information:
|
||
Magic number(s):
|
||
File extension(s): .siv
|
||
Macintosh File Type Code(s):
|
||
Person & email address to contact for further information:
|
||
See the discussion list at ietf-mta-filters@imc.org.
|
||
Intended usage:
|
||
COMMON
|
||
Author/Change controller:
|
||
See Author information in RFC 3028.
|
||
|
||
8. Parsing
|
||
|
||
The Sieve grammar is separated into tokens and a separate grammar as
|
||
most programming languages are.
|
||
|
||
8.1. Lexical Tokens
|
||
|
||
Sieve scripts are encoded in UTF-8. The following assumes a valid
|
||
UTF-8 encoding; special characters in Sieve scripts are all ASCII.
|
||
|
||
The following are tokens in Sieve:
|
||
|
||
- identifiers
|
||
- tags
|
||
- numbers
|
||
- quoted strings
|
||
- multi-line strings
|
||
- other separators
|
||
|
||
Blanks, horizontal tabs, CRLFs, and comments ("white space") are
|
||
ignored except as they separate tokens. Some white space is required
|
||
to separate otherwise adjacent tokens and in specific places in the
|
||
multi-line strings.
|
||
|
||
The other separators are single individual characters, and are
|
||
mentioned explicitly in the grammar.
|
||
|
||
The lexical structure of sieve is defined in the following BNF (as
|
||
described in [ABNF]):
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 30]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
bracket-comment = "/*" *(CHAR-NOT-STAR / ("*" CHAR-NOT-SLASH)) "*/"
|
||
;; No */ allowed inside a comment.
|
||
;; (No * is allowed unless it is the last character,
|
||
;; or unless it is followed by a character that isn't a
|
||
;; slash.)
|
||
|
||
CHAR-NOT-DOT = (%x01-09 / %x0b-0c / %x0e-2d / %x2f-ff)
|
||
;; no dots, no CRLFs
|
||
|
||
CHAR-NOT-CRLF = (%x01-09 / %x0b-0c / %x0e-ff)
|
||
|
||
CHAR-NOT-SLASH = (%x00-57 / %x58-ff)
|
||
|
||
CHAR-NOT-STAR = (%x00-51 / %x53-ff)
|
||
|
||
comment = bracket-comment / hash-comment
|
||
|
||
hash-comment = ( "#" *CHAR-NOT-CRLF CRLF )
|
||
|
||
identifier = (ALPHA / "_") *(ALPHA DIGIT "_")
|
||
|
||
tag = ":" identifier
|
||
|
||
number = 1*DIGIT [QUANTIFIER]
|
||
|
||
QUANTIFIER = "K" / "M" / "G"
|
||
|
||
quoted-string = DQUOTE *CHAR DQUOTE
|
||
;; in general, \ CHAR inside a string maps to CHAR
|
||
;; so \" maps to " and \\ maps to \
|
||
;; note that newlines and other characters are all allowed
|
||
;; strings
|
||
|
||
multi-line = "text:" *(SP / HTAB) (hash-comment / CRLF)
|
||
*(multi-line-literal / multi-line-dotstuff)
|
||
"." CRLF
|
||
multi-line-literal = [CHAR-NOT-DOT *CHAR-NOT-CRLF] CRLF
|
||
multi-line-dotstuff = "." 1*CHAR-NOT-CRLF CRLF
|
||
;; A line containing only "." ends the multi-line.
|
||
;; Remove a leading '.' if followed by another '.'.
|
||
|
||
white-space = 1*(SP / CRLF / HTAB) / comment
|
||
|
||
8.2. Grammar
|
||
|
||
The following is the grammar of Sieve after it has been lexically
|
||
interpreted. No white space or comments appear below. The start
|
||
symbol is "start".
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 31]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
argument = string-list / number / tag
|
||
|
||
arguments = *argument [test / test-list]
|
||
|
||
block = "{" commands "}"
|
||
|
||
command = identifier arguments ( ";" / block )
|
||
|
||
commands = *command
|
||
|
||
start = commands
|
||
|
||
string = quoted-string / multi-line
|
||
|
||
string-list = "[" string *("," string) "]" / string ;; if
|
||
there is only a single string, the brackets are optional
|
||
|
||
test = identifier arguments
|
||
|
||
test-list = "(" test *("," test) ")"
|
||
|
||
9. Extended Example
|
||
|
||
The following is an extended example of a Sieve script. Note that it
|
||
does not make use of the implicit keep.
|
||
|
||
#
|
||
# Example Sieve Filter
|
||
# Declare any optional features or extension used by the script
|
||
#
|
||
require ["fileinto", "reject"];
|
||
|
||
#
|
||
# Reject any large messages (note that the four leading dots get
|
||
# "stuffed" to three)
|
||
#
|
||
if size :over 1M
|
||
{
|
||
reject text:
|
||
Please do not send me large attachments.
|
||
Put your file on a server and send me the URL.
|
||
Thank you.
|
||
.... Fred
|
||
.
|
||
;
|
||
stop;
|
||
}
|
||
#
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 32]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
# Handle messages from known mailing lists
|
||
# Move messages from IETF filter discussion list to filter folder
|
||
#
|
||
if header :is "Sender" "owner-ietf-mta-filters@imc.org"
|
||
{
|
||
fileinto "filter"; # move to "filter" folder
|
||
}
|
||
#
|
||
# Keep all messages to or from people in my company
|
||
#
|
||
elsif address :domain :is ["From", "To"] "example.com"
|
||
{
|
||
keep; # keep in "In" folder
|
||
}
|
||
|
||
#
|
||
# Try and catch unsolicited email. If a message is not to me,
|
||
# or it contains a subject known to be spam, file it away.
|
||
#
|
||
elsif anyof (not address :all :contains
|
||
["To", "Cc", "Bcc"] "me@example.com",
|
||
header :matches "subject"
|
||
["*make*money*fast*", "*university*dipl*mas*"])
|
||
{
|
||
# If message header does not contain my address,
|
||
# it's from a list.
|
||
fileinto "spam"; # move to "spam" folder
|
||
}
|
||
else
|
||
{
|
||
# Move all other (non-company) mail to "personal"
|
||
# folder.
|
||
fileinto "personal";
|
||
}
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 33]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
10. Security Considerations
|
||
|
||
Users must get their mail. It is imperative that whatever method
|
||
implementations use to store the user-defined filtering scripts be
|
||
secure.
|
||
|
||
It is equally important that implementations sanity-check the user's
|
||
scripts, and not allow users to create on-demand mailbombs. For
|
||
instance, an implementation that allows a user to reject or redirect
|
||
multiple times to a single message might also allow a user to create
|
||
a mailbomb triggered by mail from a specific user. Site- or
|
||
implementation-defined limits on actions are useful for this.
|
||
|
||
Several commands, such as "discard", "redirect", and "fileinto" allow
|
||
for actions to be taken that are potentially very dangerous.
|
||
|
||
Implementations SHOULD take measures to prevent languages from
|
||
looping.
|
||
|
||
11. Acknowledgments
|
||
|
||
I am very thankful to Chris Newman for his support and his ABNF
|
||
syntax checker, to John Myers and Steve Hole for outlining the
|
||
requirements for the original drafts, to Larry Greenfield for nagging
|
||
me about the grammar and finally fixing it, to Greg Sereda for
|
||
repeatedly fixing and providing examples, to Ned Freed for fixing
|
||
everything else, to Rob Earhart for an early implementation and a
|
||
great deal of help, and to Randall Gellens for endless amounts of
|
||
proofreading. I am grateful to Carnegie Mellon University where most
|
||
of the work on this document was done. I am also indebted to all of
|
||
the readers of the ietf-mta-filters@imc.org mailing list.
|
||
|
||
12. Author's Address
|
||
|
||
Tim Showalter
|
||
Mirapoint, Inc.
|
||
909 Hermosa Court
|
||
Sunnyvale, CA 94085
|
||
|
||
EMail: tjs@mirapoint.com
|
||
|
||
13. References
|
||
|
||
[ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax
|
||
Specifications: ABNF", RFC 2234, November 1997.
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 34]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
[ACAP] Newman, C. and J. G. Myers, "ACAP -- Application
|
||
Configuration Access Protocol", RFC 2244, November 1997.
|
||
|
||
[BINARY-SI] "Standard IEC 60027-2: Letter symbols to be used in
|
||
electrical technology - Part 2: Telecommunications and
|
||
electronics", January 1999.
|
||
|
||
[DSN] Moore, K. and G. Vaudreuil, "An Extensible Message Format
|
||
for Delivery Status Notifications", RFC 1894, January
|
||
1996.
|
||
|
||
[FLAMES] Borenstein, N, and C. Thyberg, "Power, Ease of Use, and
|
||
Cooperative Work in a Practical Multimedia Message
|
||
System", Int. J. of Man-Machine Studies, April, 1991.
|
||
Reprinted in Computer-Supported Cooperative Work and
|
||
Groupware, Saul Greenberg, editor, Harcourt Brace
|
||
Jovanovich, 1991. Reprinted in Readings in Groupware and
|
||
Computer-Supported Cooperative Work, Ronald Baecker,
|
||
editor, Morgan Kaufmann, 1993.
|
||
|
||
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
|
||
Requirement Levels", BCP 14, RFC 2119, March 1997.
|
||
|
||
[IMAP] Crispin, M., "Internet Message Access Protocol - version
|
||
4rev1", RFC 2060, December 1996.
|
||
|
||
[IMAIL] Crocker, D., "Standard for the Format of ARPA Internet
|
||
Text Messages", STD 11, RFC 822, August 1982.
|
||
|
||
[MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
|
||
Extensions (MIME) Part One: Format of Internet Message
|
||
Bodies", RFC 2045, November 1996.
|
||
|
||
[MDN] Fajman, R., "An Extensible Message Format for Message
|
||
Disposition Notifications", RFC 2298, March 1998.
|
||
|
||
[RFC1123] Braden, R., "Requirements for Internet Hosts --
|
||
Application and Support", STD 3, RFC 1123, November 1989.
|
||
|
||
[SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC
|
||
821, August 1982.
|
||
|
||
[UTF-8] Yergeau, F., "UTF-8, a transformation format of Unicode
|
||
and ISO 10646", RFC 2044, October 1996.
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 35]
|
||
|
||
RFC 3028 Sieve: A Mail Filtering Language January 2001
|
||
|
||
|
||
14. Full Copyright Statement
|
||
|
||
Copyright (C) The Internet Society (2001). All Rights Reserved.
|
||
|
||
This document and translations of it may be copied and furnished to
|
||
others, and derivative works that comment on or otherwise explain it
|
||
or assist in its implementation may be prepared, copied, published
|
||
and distributed, in whole or in part, without restriction of any
|
||
kind, provided that the above copyright notice and this paragraph are
|
||
included on all such copies and derivative works. However, this
|
||
document itself may not be modified in any way, such as by removing
|
||
the copyright notice or references to the Internet Society or other
|
||
Internet organizations, except as needed for the purpose of
|
||
developing Internet standards in which case the procedures for
|
||
copyrights defined in the Internet Standards process must be
|
||
followed, or as required to translate it into languages other than
|
||
English.
|
||
|
||
The limited permissions granted above are perpetual and will not be
|
||
revoked by the Internet Society or its successors or assigns.
|
||
|
||
This document and the information contained herein is provided on an
|
||
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
|
||
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
|
||
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
|
||
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
|
||
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
|
||
|
||
Acknowledgement
|
||
|
||
Funding for the RFC Editor function is currently provided by the
|
||
Internet Society.
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Showalter Standards Track [Page 36]
|
||
|