< draft-melnikov-sieve-external-lists-01.txt   draft-melnikov-sieve-external-lists-02.txt >
Sieve Working Group A. Melnikov Sieve Working Group A. Melnikov
Internet-Draft Isode Limited Internet-Draft Isode Limited
Intended status: Standards Track July 6, 2007 Intended status: Standards Track July 5, 2009
Expires: January 7, 2008 Expires: January 6, 2010
Sieve Extension: Externally Stored Lists Sieve Extension: Externally Stored Lists
draft-melnikov-sieve-external-lists-01 draft-melnikov-sieve-external-lists-02
Status of this Memo Status of this Memo
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Abstract Abstract
Sieve scripting language can be used for implementing of Sieve scripting language can be used for implementing of
whitelisting, blacklisting and personal distribution lists. whitelisting, blacklisting and personal distribution lists.
Currently this requires that all members of such lists be hardcoded Currently this requires that all members of such lists be hardcoded
in the script itself. Whenever a member of such list is added or in the script itself. Whenever a member of such list is added or
deleted, the script needs to be updated and possibly uploaded to a deleted, the script needs to be updated and possibly uploaded to a
mail server. mail server.
skipping to change at page 2, line 26 skipping to change at page 2, line 31
1.1. Conventions used in this document . . . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . . . 3
2. Extlists extension . . . . . . . . . . . . . . . . . . . . . 3 2. Extlists extension . . . . . . . . . . . . . . . . . . . . . 3
2.1. Capability Identifier . . . . . . . . . . . . . . . . . . . . 3 2.1. Capability Identifier . . . . . . . . . . . . . . . . . . . . 3
2.2. :list tagged argument to the 'address', 'header' and 2.2. :list tagged argument to the 'address', 'header' and
'envelope' tests . . . . . . . . . . . . . . . . . . . . . . 3 'envelope' tests . . . . . . . . . . . . . . . . . . . . . . 3
2.3. :list tagged argument to the 'redirect' action . . . . . . . 4 2.3. :list tagged argument to the 'redirect' action . . . . . . . 4
2.4. Syntax of an externally stored list name . . . . . . . . . . 4 2.4. Syntax of an externally stored list name . . . . . . . . . . 4
2.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4 3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . . . 6 6.1. Normative References . . . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . . . 6 6.2. Informative References . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . 7
1. Introduction 1. Introduction
This document specified an extension to the Sieve language defined by This document specified an extension to the Sieve language defined by
[Sieve] for checking membership in an externally stored list or for [Sieve] for checking membership in an externally stored list or for
sending messages to a list of recipients stored externally to the sending messages to a list of recipients stored externally to the
Sieve script. Sieve script.
This extension adds a new tagged argument to the "header" and This extension adds a new tagged argument to the "header" and
"envelope" tests, and to the "redirect" action [Sieve]. "envelope" tests, and to the "redirect" action [Sieve].
skipping to change at page 4, line 23 skipping to change at page 4, line 23
The "redirect" action with the ":list" argument is used to send the The "redirect" action with the ":list" argument is used to send the
message to one or more email address stored in the externally stored message to one or more email address stored in the externally stored
list 'ext-list-name'. This variant of the redirect command can be list 'ext-list-name'. This variant of the redirect command can be
used to implement a personal distribution list. used to implement a personal distribution list.
See Section 2.4 for the detailed description of syntax used for See Section 2.4 for the detailed description of syntax used for
naming externally stored lists. naming externally stored lists.
2.4. Syntax of an externally stored list name 2.4. Syntax of an externally stored list name
[[anchor5: Specify ABNF. Dave Cridland has suggested to use a A name of an externally stored list is always an absolute URI.
leading ':' for "opaque" identifiers.]] Implementations might find URL such as [LDAP], [CardDAV] URL), or
[TAG-URI] to be useful for naming external lists.
A name of an externally stored list is either an absolute URL (e.g. The "tag" URI scheme can be used to represent opaque, but user
an [LDAP], [ACAP] or [CardDAV] URL) or an opaque identifier. friendlier identifiers. Resolution of such identifiers is going to
Interpretation of opaque identifiers is left up to implementations. be implementation specific and it can help in hiding the complexity
They can hide complexity of an implementation from end users. For of an implementation from end users. For example, an implementation
example, an implementation can provide a web interface for managing can provide a web interface for managing lists of users stored in
lists of users stored in LDAP. Requiring users to know syntax for LDAP. Requiring users to know generic LDAP URL syntax is not going
LDAP URLs is just not very practical. to be very practical, due to its complexity. However such
implementation can use a fixed tag URI prefix such as "tag:
example.com,<date>:" (where <date> can be, for example, a date
generated once on installation of the web interface and left
untouched upon upgrades) instead and the prefix doesn't even need to
be shown to end users.
2.5. Examples 2.5. Examples
Example 1: Example 1:
require ["extlists"]; require ["extlists"];
# Submission from list members is sent to all members # Submission from list members is sent to all members
if allof (envelope :detail :list "to" "mylist", if allof (envelope :detail :list "to"
header :contains :list "from" "mylist") { "tag:example.com,2009-05-28:mylist",
redirect :list "mylist"; header :contains :list "from"
"tag:example.com,2009-05-28:mylist") {
redirect :list "tag:example.com,2009-05-28:mylist";
} }
3. Security Considerations 3. Security Considerations
Security considerations are discussed in [Sieve]. Security considerations related to the "envelope"/"header" tests and
"redirect" action discussed in [Sieve] also apply to this document.
[[anchor6: Describe risks of external lists including thousands of A failure to retrieve data due to the server storing the external
recipients.]] [[anchor7: Describe how to handle outages of servers list membership being down or otherwise inaccessible may alter the
providing access to an externally stored list.]] result of Sieve processing. So implementations SHOULD treat a
temporary failure to retrieve or verify external list membership in
the same manner as a temporary failure to retrieve a Sieve script.
For example, if the Sieve script is stored in the Lightweight
Directory Access Protocol (LDAP) and the script can't be retrieved
when a message is processed, then the agent performing Sieve
processing can, for example, assume that the script doesn't exist or
delay message delivery until the script can be retrieved
successfully. External list memberships should be treated as if they
are a part of the script itself, so a temporary failure to retrieve
them should be handled in the same way as a temporary failure to
retrieve the Sieve script itself.
Protocols/APIs used to retrieve/verify external list membership MUST
provide at least the same level of confidentiality as protocols/APIs
used to retrieve Sieve scripts. For example, if Sieve scripts are
retrieved using LDAP secured with Transport Layer Security (TLS)
encryption, then the protocol used to retrieve external list
membership must use a comparable mechanism for providing connection
confidentiality. In particular, the protocol used to retrieve
external list membership must not be lacking encryption.
Implementations of this extensions should keep in mind that matching Implementations of this extensions should keep in mind that matching
values against an externally stored list can be IO and/or CPU values against an externally stored list can be IO and/or CPU
intensive. This can be used to deny service to the mailserver and/or intensive. This can be used to deny service to the mailserver and/or
to servers providing access to externally stored mailing lists. A to servers providing access to externally stored mailing lists. A
naive implementation, such as the one that tries to retrieve content naive implementation, such as the one that tries to retrieve content
of the whole list to perform matching can make this worse. But note of the whole list to perform matching can make this worse. But note
that many protocols that can be used for accessing externally stored that many protocols that can be used for accessing externally stored
lists support flexible searching facilities that can be used to lists support flexible searching facilities that can be used to
minimize network traffic. For example LDAP allows for search minimize network traffic and load on the directory service. For
filters. example LDAP allows for search filters.
In order to avoid mailbombs, when redirecting a message to an Many organizations support external lists with thousands of
externally stored mailing list, implementations SHOULD enforce limits recipients. In order to avoid mailbombs, when redirecting a message
on the number of recipients and/or on domains to which such to an externally stored mailing list, implementations SHOULD enforce
limits on the number of recipients and/or on domains to which such
recipients belong. recipients belong.
4. IANA Considerations 4. IANA Considerations
The following template specifies the IANA registration of the notify The following template specifies the IANA registration of the notify
Sieve extension specified in this document: Sieve extension specified in this document:
To: iana@iana.org To: iana@iana.org
Subject: Registration of new Sieve extension Subject: Registration of new Sieve extension
Capability name: extlists Capability name: extlists
skipping to change at page 6, line 10 skipping to change at page 6, line 38
Thanks to Alexandros Vellis, Barry Leiba, Nigel Swinson, Kjetil Thanks to Alexandros Vellis, Barry Leiba, Nigel Swinson, Kjetil
Torgrim Homme, Dave Cridland, Cyrus Daboo, Pete Resnick for ideas, Torgrim Homme, Dave Cridland, Cyrus Daboo, Pete Resnick for ideas,
comments and suggestions. comments and suggestions.
6. References 6. References
6.1. Normative References 6.1. Normative References
[ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005. Specifications: ABNF", RFC 5234, January 2008.
[Kwds] Bradner, S., "Key words for use in RFCs to Indicate [Kwds] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997. Requirement Levels", RFC 2119, March 1997.
[Sieve] Guenther, P. and T. Showalter, "Sieve: An Email Filtering [Sieve] Guenther, P. and T. Showalter, "Sieve: An Email Filtering
Language", work in progress, draft-ietf-sieve-3028bis, Language", RFC 5228, January 2008.
August 2006.
[URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005. RFC 3986, January 2005.
6.2. Informative References 6.2. Informative References
[ACAP] Newman, C. and J. Myers, "ACAP -- Application [ACAP] Newman, C. and J. Myers, "ACAP -- Application
Configuration Access Protocol", RFC 2244, November 1997. Configuration Access Protocol", RFC 2244, November 1997.
[CardDAV] Daboo, C., "vCard Extensions to WebDAV (CardDAV)", work in [CardDAV] Daboo, C., "vCard Extensions to WebDAV (CardDAV)", work in
progress, draft-daboo-carddav, May 2007. progress, draft-daboo-carddav, May 2007.
[LDAP] Zeilenga, K., "Lightweight Directory Access Protocol [LDAP] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP): Technical Specification Road Map", RFC 4510, (LDAP): Technical Specification Road Map", RFC 4510,
June 2006. June 2006.
[TAG-URI] Kindberg, T. and S. Hawke, "The 'tag' URI Scheme",
RFC 4151, October 2005.
Author's Address Author's Address
Alexey Melnikov Alexey Melnikov
Isode Limited Isode Limited
5 Castle Business Village 5 Castle Business Village
36 Station Road 36 Station Road
Hampton, Middlesex TW12 2BX Hampton, Middlesex TW12 2BX
UK UK
Email: Alexey.Melnikov@isode.com Email: Alexey.Melnikov@isode.com
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