Pigeonhole for Dovecot v2.2

Introduction
============

This package is part of the Pigeonhole project (http://pigeonhole.dovecot.org).
It adds support for the Sieve language (RFC 5228) and the ManageSieve protocol
(RFC 5804) to the Dovecot Secure IMAP Server. In the literal sense, a pigeonhole
is a a hole or recess inside a dovecot for pigeons to nest in. It is, however,
also the name for one of a series of small, open compartments in a cabinet used
for filing or sorting mail. As a verb, it describes the act of putting an item
into one of those pigeonholes. The name `Pigeonhole' therefore well describes an
important part of the functionality that this project adds to Dovecot: sorting
and filing e-mail messages.

The Sieve language is used to specify how e-mail needs to be processed. By
writing Sieve scripts, users can customize how messages are delivered, e.g.
whether they are forwarded or stored in special folders. Unwanted messages can
be discarded or rejected, and, when the user is not available, the Sieve
interpreter can send an automated reply. Above all, the Sieve language is meant
to be simple, extensible and system independent. And, unlike most other mail
filtering script languages, it does not allow users to execute arbitrary
programs. This is particularly useful to prevent virtual users from having full
access to the mail store. The intention of the language is to make it impossible
for users to do anything more complex (and dangerous) than write simple mail
filters.

Using the ManageSieve protocol, users can upload their Sieve scripts remotely,
without needing direct filesystem access through FTP or SCP. Additionally, a
ManageSieve server always makes sure that uploaded scripts are valid, preventing
compile failures at mail delivery.

This package provides Sieve support as a plugin to Dovecot's Local Delivery
Agent (LDA) and Dovecot's LMTP service. The ManageSieve protocol is provided is
an additional service, next to Dovecot's own POP3 and IMAP services.

Features
========

  * The Pigeonhole Sieve implementation aims to be admin- and user-friendly.
    Much like Dovecot itself, common error messages are made as easily
    understandable as possible. Any crash, no matter how it happened, is
    considered a bug that will be fixed. The compiler does not bail on the first
    error, but it looks for more script errors to make debugging more efficient.

  * The Pigeonhole Sieve implementation is, much like the Sieve language itself,
    highly extensible with new Sieve capabilities. This includes support for
    third-party plugins. It should eventually provide the necessary
    infrastructure for at least all currently known relevant (proposed) Sieve
    extensions. The goal is to keep the extension interface provided by the
    Sieve implementation as generic as possible, i.e. without explicit support
    for specific extensions. New similar extensions can then use the same
    interface methods without changes to the Sieve engine code. If an extension
    is not loaded using the require command, the compiler truly does not know of
    its existence.

  * The Pigeonhole Sieve plugin is backwards compatible with the old CMUSieve
    plugin, which provided Sieve support for older versions of Dovecot. All
    Sieve extensions supported by the old plugin are also supported by the
    Pigeonhole Sieve plugin, including those that are now considered to be
    deprecated.

  * The Pigeonhole Sieve implementation supports executing multiple Sieve
    scripts sequentially. Using this feature it is possible to execute
    administrator-controlled Sieve scripts before and after the user's personal
    Sieve script, guaranteeing that responses and message deliveries are never
    duplicated. This implementation is based on a draft specification
    (http://tools.ietf.org/html/draft-degener-sieve-multiscript-00), which
    defines the Sieve behavior when multiple scripts are executed sequentially
    on the same message.

  * The Pigeonhole Sieve implementation includes a test suite to automatically
    assess whether the compiled Sieve engine works correctly. The test suite is
    an extension to the Sieve language and is therefore easily extended with new
    tests. Currently, the test suite is mostly limited to testing script
    processing. The performed actions are not tested fully yet.

  * The Pigeonhole Sieve implementation supports the new and very useful
    variables extension, which allows maintaining state information throughout
    a Sieve script across subsequent rules.

  * The Pigeonhole Sieve plugin is distributed with a sieve-test tool that
    simplifies testing Sieve scripts and provides additional debugging
    facilities.

Sieve Implementation Status
===========================

The core of the language (as specified in RFC 5228) is fully supported. In
addition to that, this Sieve implementation features various extensions. The
following list outlines the implementation status of each supported extension:

  The language extensions defined in the base specification are fully supported:

    encoded-character (RFC 5228; page 10)
    fileinto (RFC 5228; page 23)
    envelope (RFC 5228; page 27)

  The following Sieve language extensions are also supported:

    copy (RFC 3894): fully supported.
    body (RFC 5173): almost fully supported, but the text body-transform
        implementation is simple.
    environment (RFC 5183): fully supported (v0.4.0+).
    variables (RFC 5229): fully supported.
    vacation (RFC 5230): fully supported.
      + vacation-seconds (RFC 6131): fully supported (v0.2.3+).
    relational (RFC 5231): fully supported.
    imap4flags (RFC 5232): fully supported.
    subaddress (RFC 5233): fully supported, but with limited configurability.
    spamtest and virustest (RFC 5235): fully supported (v0.1.16+).
    date (RFC 5260; Section 4): fully supported (v0.1.12+).
    editheader (RFC 5293): fully supported (v0.3.0+).
    reject (RFC 5429; Section 2.2): fully supported.
    enotify (RFC 5435): fully supported (v0.1.3+).
        mailto method (RFC 5436): fully supported (v0.1.3+).
        xmpp method (RFC 5437): is under development and will become available
          as a plugin.
    ihave (RFC 5463): fully supported (v0.2.4+).
    mailbox (RFC 5490; Section 3): fully supported (v0.1.10+), but ACL
        permissions are not verified for mailboxexists.
    include (RFC 6609): fully supported (v0.4.0+)
    regex (draft v08; not latest version): almost fully supported, but
        UTF-8 is not supported.

  The following deprecated extensions are supported for backwards
  compatibility:

    imapflags (obsolete draft): fully backwards compatible (v0.1.3+)
    notify (obsolete draft): fully backwards compatible (v0.1.15+)

    The availability of these deprecated extensions is disabled by default.

  The following Dovecot-specific Sieve extensions are available:

    vnd.dovecot.debug (v0.3.0+):
        Allows logging debug messages
    vnd.dovecot.duplicate (v0.3.1+):
        Allows detecting duplicate message deliveries based on message ID and
        other criteria.
    vnd.dovecot.pipe (v0.4.0+; sieve_extprograms plugin):
        Implements piping messages to a pre-defined set of external programs
    vnd.dovecot.filter (v0.4.0+; sieve_extprograms plugin):
        Implements filtering messages through a pre-defined set of external
        programs
    vnd.dovecot.execute (v0.4.0+; sieve_extprograms plugin):
        Implements executing a pre-defined set of external programs with the
        option to process string data through the external program 

  The following extensions are under development:

    ereject (RFC 5429; page 4): implemented, but currently equal to reject

  Many more extensions to the language exist. Not all of these extensions are
  useful for Dovecot in particular, but many of them are. Currently, the
  author has taken notice of the following extensions:

    index (RFC 5260; page 7): planned.
    foreverypart, mime, replace, enclose, and extracttext (RFC 5703): planned.

    These extensions will be added as soon as the necessary infrastructure is
    available.

Compiling and Configuring
=========================

Refer to INSTALL file.

Sieve Tools
===========

To test the sieve engine outside deliver, it is useful to try the commands that
exist in the src/sieve-tools/ directory of this package. After installation,
these are available at your $prefix/bin directory. The following commands are
installed:

sievec       - Compiles sieve scripts into a binary representation for later
               execution. Refer to the next section on manually compiling Sieve
               scripts.

sieve-test   - This is a universal Sieve test tool for testing the effect of a
               Sieve script on a particular message. It allows compiling,
               running and testing Sieve scripts. It can either be used to
               display the actions that would be performed on the provided test
               message or it can be used to test the actual delivery of the
               message and show the messages that would normally be sent through
               SMTP.

sieve-dump   - Dumps the content of a Sieve binary file for (development)
               debugging purposes.

sieve-filter - Allow running Sieve filters on messages already stored in a
               mailbox. 

When installed, man pages are also available for these commands. In this package
the man pages are present in doc/man and can be viewed before install using
e.g.:

man -l doc/man/sieve-test.1

Various example scripts are bundled in the directory 'examples'. These scripts
were downloaded from various locations. View the top comment in the scripts for
url and author information.

Compiling Sieve Scripts
=======================

When the LDA Sieve plugin executes a script for the first time (or after it has
been changed), it is compiled into into a binary form. The Pigeonhole Sieve
implementation uses the .svbin extension to store compiled Sieve scripts (e.g.
.dovecot.svbin). To store the binary, the plugin needs write access in the
directory in which the script is located.

A problem occurs when a global script is encountered by the plugin. For security
reasons, global script directories are not supposed to be writable by the user.
Therefore, the plugin cannot store the binary when the script is first compiled.
Note that this doesn't mean that the old compiled version of the script is used
when the binary cannot be written: it compiles and uses the current script
version. The only real problem is that the plugin will not be able to update
the binary on disk, meaning that the global script needs to be recompiled each
time it needs to be executed, i.e. for every incoming message, which is
inefficient.

To mitigate this problem, the administrator must manually pre-compile global
scripts using the sievec command line tool. For example:

sievec /var/lib/dovecot/sieve/global/

This is often necessary for scripts listed in the sieve_default, sieve_before
and sieve_after settings. For global scripts that are only included in other
scripts using the include extension, this step is not necessary, since included
scripts are incorporated into the binary produced for the main script located in
a user directory.

Compile and Runtime Logging
===========================

Log messages produced at runtime by the Sieve plugin are written to two
locations:

  * A log file is written in the same directory as the user's main private
    script (as specified by the sieve setting). This log file bears the name of
    that script file appended with ".log", e.g. .dovecot.sieve.log. If there are
    errors or warnings in the script, the messages are appended to that log file
    until it eventually grows too large. When that happens, the old log file is
    rotated to a ".log.0" file and an empty log file is started. Informational
    messages are not written to this log file and the log file is not created
    until messages are actually logged, i.e. when an error or warning is
    produced.

  * Messages that could be of interest to the system administrator are also
    written to the Dovecot LDA logging facility (usually syslog). This includes
    informational messages that indicate what actions are executed on incoming
    messages. Compile errors encountered in the user's private script are not
    logged here.

The ManageSieve service reports compile errors and warnings only back to the
user. System and configuration-related messages are written to the Dovecot
logging facility.

Known issues
============

Sieve
-----

Most open issues are outlined in the TODO file. The more generic ones are (re-)
listed here:

* Compile errors are sometimes a bit obscure and long. This needs work.
  Suggestions for improvement are welcome.

* The documentation needs work.

ManageSieve
-----------

* Although this ManageSieve server should comply with the draft specification of
  the ManageSieve protocol, quite a few clients don't. This is particularly true
  for the TLS support. However, now that Cyrus' Timsieved has changed its
  behavior towards protocol compliance, all those clients will follow
  eventually.

  Clients known to have TLS issues:
	- Thunderbird Sieve add-on: fixed as per version 0.1.5
	- AvelSieve: patch on the wiki:	http://wiki.dovecot.org/ManageSieve
	- KMail + kio_sieve: TLS broken for old versions. This issue is fixed at
	  least in kmail 1.9.9 / kde 3.5.9.

  Unfortunately, there is no reliable way to provide a workaround for this
  problem. We will have to wait for the authors of these clients to make the
  proper adjustments.

* Other client issues:

	- SmartSieve, WebSieve:
	  These clients are specifically written for Cyrus timsieved and fail on
	  multiple stages of the protocol when connected to Pigeonhole ManageSieve.

Authors
=======

Refer to AUTHORS file.

Contact Info
============

Stephan Bosch <stephan at rename-it dot nl>
IRC: Freenode, #dovecot, S[r]us
Web: http://pigeonhole.dovecot.org

Please use the Dovecot mailing list <dovecot at dovecot.org> for questions about
this package. You can post to the list without subscribing, the mail then waits
in a moderator queue for a while. See http://dovecot.org/mailinglists.html