S. Bosch
                                                      September 29, 2016


          Sieve Email Filtering: Dovecot Environment Extension
                  spec-bosch-sieve-dovecot-environment

Abstract

   This document defines new vendor-defined items for the "environment"
   extension of the Sieve mail filtering language.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   1
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   1
   3.  Dovecot Environment Items . . . . . . . . . . . . . . . . . .   2
   4.  Variables Namespace env . . . . . . . . . . . . . . . . . . .   2
   5.  Sieve Capability Strings  . . . . . . . . . . . . . . . . . .   3
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   3
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   3

1.  Introduction

   This document describes an extension to the Sieve filtering language
   defined by RFC 5228 [SIEVE].  This vendor-defined extension builds
   upon the existing standard "environment" extension [ENVIRONMENT],
   which allows Sieve scripts to access information about their
   execution context, such as the name and version of the Sieve
   interpreter implementation.  The new "vnd.dovecot.environment"
   extension adds a few more environment items that can be accessed by
   Sieve scripts.  Additionally, it makes the environment items
   available directly as variables [VARIABLES].

   This extension is specific to the Pigeonhole Sieve implementation for
   the Dovecot Secure IMAP server.  It will therefore most likely not be
   supported by web interfaces and GUI-based Sieve editors.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [KEYWORDS].

   Conventions for notations are as in [SIEVE] Section 1.1, including
   use of the "Usage:" label for the definition of action and tagged
   arguments syntax.



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3.  Dovecot Environment Items

   The set of Dovecot-specific environment items is as follows:

   "vnd.dovecot.default-mailbox"
         The default mailbox that is used by the (implicit) keep action.
         Normally, this will always yield "INBOX", unless this is
         changed in the configuration.

   "vnd.dovecot.username"
         The username of the recipient for this particular message
         delivery.

   "vnd.dovecot.config.*"
         This environment item obtains its value from the mail server
         configuration.  The part of the environment item name after the
         "vnd.dovecot.config." prefix is used as an identifier of the
         configuration setting.  This will only be able to access
         settings within a limited namespace, e.g. settings with a
         particular identifier prefix.

4.  Variables Namespace env

   This document defines the variables namespace "env", in accordance
   with the "variables" extension document [VARIABLES], Section 3.  It
   makes environment items directly available as variables.  Since
   environment items are always read-only, variables in the "env"
   namespace can never be modified.

   Basically, the variable name for an environment item is composed of
   the "env." namespace prefix followed by the full name of the
   environment item.  This is also true when the environment item name
   contains "." characters; those have no special meaning within the
   "env" variables namespace.  However, since a variable name cannot
   contain "-" characters, any "-" character in the name of the
   environment item is mapped to an "_" character.  The environment item
   called "vnd.dovecot.default-mailbox" is therefore available as the
   variable "${env.vnd.dovecot.default_mailbox}".

   Example:

   require ["variables", "fileinto", "mailbox"];
   require "vnd.dovecot.environment";

   fileinto :create "User\${env.vnd.dovecot.username}";






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5.  Sieve Capability Strings

   A Sieve implementation that supports the Dovecot-specific environment
   items outlined in this document will advertise the capability string
   "vnd.dovecot.environment".  Note that "vnd.dovecot.environment"
   implies "environment", and a script with "vnd.dovecot.environment" in
   a "require" list can omit "environment" from that list.

6.  Security Considerations

   All of the security considerations given in the base Sieve
   specification [SIEVE] and the specification of the "environment"
   extension [ENVIRONMENT] also apply to this extension.  Some of the
   environment items added by this extension are somewhat more sensitive
   than the standard ones, so enabling this extension should be
   considered carefully.

7.  Normative References

   [ENVIRONMENT]
              Freed, N., "Sieve Email Filtering: Environment Extension",
              RFC 5183, DOI 10.17487/RFC5183, May 2008,
              <http://www.rfc-editor.org/info/rfc5183>.

   [KEYWORDS]
              Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [SIEVE]    Guenther, P. and T. Showalter, "Sieve: An Email Filtering
              Language", RFC 5228, January 2008.

   [VARIABLES]
              Homme, K., "Sieve Email Filtering: Variables Extension",
              RFC 5229, January 2008.

Author's Address

   Stephan Bosch
   Enschede
   NL

   Email: stephan@rename-it.nl









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