draft-ietf-sieve-external-lists-00.txt   draft-ietf-sieve-external-lists-01.txt 
Sieve Working Group A. Melnikov Sieve Working Group A. Melnikov
Internet-Draft Isode Limited Internet-Draft Isode Limited
Intended status: Standards Track July 5, 2009 Intended status: Standards Track B. Leiba
Expires: January 6, 2010 Expires: March 1, 2010 Huawei Technologies
August 28, 2009
Sieve Extension: Externally Stored Lists Sieve Extension: Externally Stored Lists
draft-ietf-sieve-external-lists-00 draft-ietf-sieve-external-lists-01
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
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Abstract Abstract
Sieve scripting language can be used for implementing of The Sieve scripting language can be used to implement whitelisting,
whitelisting, blacklisting and personal distribution lists. blacklisting, and personal distribution lists. Currently, this
Currently this requires that all members of such lists be hardcoded requires that all members of such lists be hardcoded in the script
in the script itself. Whenever a member of such list is added or itself. Whenever a member of a list is added or deleted, the script
deleted, the script needs to be updated and possibly uploaded to a needs to be updated and possibly uploaded to a mail server.
mail server.
This document defines a Sieve extension for accessing externally This document defines a Sieve extension for accessing externally
stored mailing lists, i.e. list whose members are stored externally stored lists -- lists whose members are stored externally to the
to the script, for example in LDAP (RFC 4510), ACAP (RFC 2244) or a script, such as using LDAP (RFC 4510), ACAP (RFC 2244), or relational
relational database. databases.
ToDo ToDo
o Need a way to advertise supported URI schemas in ManageSieve and o Need a way to advertise supported URI schemas in ManageSieve and
ihave. ihave.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
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 match type for "address", "envelope", and "header"
'envelope' tests . . . . . . . . . . . . . . . . . . . . . . 3 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 . . . . . . . . . . 5
2.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . 5 3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . . . 6 6.1. Normative References . . . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . . . 7 6.2. Informative References . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
This document specified an extension to the Sieve language defined by This document specifies an extension to the Sieve language [Sieve]
[Sieve] for checking membership in an externally stored list or for for checking membership in an external list or for redirecting
sending messages to a list of recipients stored externally to the messages to an external list of recipients. An "external list" is a
Sieve script. list whose members are stored externally to the Sieve script, such as
using LDAP [LDAP], ACAP [ACAP], or relational databases.
This extension adds a new tagged argument to the "header" and This extension adds a new match type to the "address", "envelope",
"envelope" tests, and to the "redirect" action [Sieve]. and "header" tests, and a new tagged argument to the "redirect"
action.
1.1. Conventions used in this document 1.1. Conventions used in this document
Conventions for notations are as in [Sieve] section 1.1, including Conventions for notations are as in [Sieve] section 1.1, including
the use of [ABNF]. the use of [ABNF].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [Kwds]. document are to be interpreted as described in [Kwds].
2. Extlists extension 2. Extlists extension
2.1. Capability Identifier 2.1. Capability Identifier
The capability string associated with the extension defined in this The capability string associated with the extension defined in this
document is "extlists". document is "extlists".
2.2. :list tagged argument to the 'address', 'header' and 'envelope' 2.2. :list match type for "address", "envelope", and "header" tests
tests
Usage: address [COMPARATOR] [ADDRESS-PART] [MATCH-TYPE] [:list] ABNF:
<header-list: string-list>
<key-list: string-list>
Usage: header [COMPARATOR] [MATCH-TYPE] [:list] MATCH-TYPE =/ ":list"
<header-names: string-list>
<key-list: string-list>
Usage: envelope [COMPARATOR] [ADDRESS-PART] [MATCH-TYPE] [:list] The new ":list" match type changes the interpretation of the "key-
<envelope-part: string-list> list" parameter (the second parameter) to the
<key-list: string-list> "address"/"envelope"/"header" test. [[anchor4: This is not quite
right. Ned convinced me that this new match type can apply to other
tests as well.]] When the match type is ":list", the key-list
becomes a list of names of externally stored lists. The external
lists are queried, perhaps through a list-specific mechanism, and the
test evaluates to "true" if any of the specified values matches any
member of one or more of the lists.
The new ":list" tagged argument, if present, changes interpretation For example, testing ':header ["to", "cc"]' against a list would
of the "key-list" parameter to the 'address'/'header'/'envelope' test cause each "to" and "cc" value, ignoring leading and trailing
to become a list of names of externally stored lists. E.g. the whitespace, to be queried. When any value is found to belong to the
"header" test with the ":list" parameter evaluates to true if the list, the queries may stop and the test returns "true". If no value
value of any of the named headers, ignoring leading and trailing belongs to the list, the test returns "false".
whitespace, matches any member of one or more externally stored lists
of values with names specified in key-list. For some lists, the Sieve engine might directly retrieve the list and
make its own comparison. Other lists might not work that way -- they
might provide a way to ask if a value is in the list, but not permit
retrieval of the list itself. It is up to the Sieve implementation
to understand how to interact with any supported list. If the Sieve
engine is permanently unable to query the list (perhaps because the
list doesn't support the required operation), the test MUST result in
a runtime error in the Sieve script.
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.
2.3. :list tagged argument to the 'redirect' action 2.3. :list tagged argument to the "redirect" action
Usage: redirect :list <ext-list-name: string> Usage: redirect :list <ext-list-name: string>
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 addresses stored in the externally
list 'ext-list-name'. This variant of the redirect command can be stored list 'ext-list-name'. This variant of the redirect command
used to implement a personal distribution list. can be used to implement a personal distribution list.
Use of this feature requires that the list resolve to a list of email
addresses, and that the Sieve engine be able to enumerate those
addresses. [[anchor6: Alexey would like the option of allowing the
list handler to enumerate the addresses and do the redirect there.
(Ned seems to agree that this should be allowed.) Barry thinks
that's contrary to Sieve, which expects to queue the redirect action
for processing at a later stage, and that it would be a bad idea to
have the redirect happen in the list handler. The WG needs to
resolve this issue.]] In cases where, for example, a list contains
hashed email address values or an email address pattern ("sz*@
example.com", "*+ietf@example.net"), it will not be possible to
redirect to that list.
If the Sieve engine [[anchor7: or list handler?]] is permanently
unable to enumerate the list or the list does not resolve to email
addresses, the situation MUST result in a runtime error in the Sieve
script.
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
A name of an externally stored list is always an absolute URI. A name of an externally stored list is always an absolute URI [URI].
Implementations might find URL such as [LDAP], [CardDAV] URL), or Implementations might find URLs such as [LDAP], [CardDAV], or
[TAG-URI] to be useful for naming external lists. [TAG-URI] to be useful for naming external lists.
The "tag" URI scheme can be used to represent opaque, but user The "tag" URI scheme [TAG-URI] can be used to represent opaque, but
friendlier identifiers. Resolution of such identifiers is going to user friendlier identifiers. Resolution of such identifiers is going
be implementation specific and it can help in hiding the complexity to be implementation specific and it can help in hiding the
of an implementation from end users. For example, an implementation complexity of an implementation from end users. For example, an
can provide a web interface for managing lists of users stored in implementation can provide a web interface for managing lists of
LDAP. Requiring users to know generic LDAP URL syntax is not going users stored in LDAP. Requiring users to know generic LDAP URL
to be very practical, due to its complexity. However such syntax might not be very practical, due to its complexity. An
implementation can use a fixed tag URI prefix such as "tag: implementation can instead use a fixed tag URI prefix such as "tag:
example.com,<date>:" (where <date> can be, for example, a date example.com,<date>:" (where <date> can be, for example, a date
generated once on installation of the web interface and left generated once on installation of the web interface and left
untouched upon upgrades) instead and the prefix doesn't even need to untouched upon upgrades) and the prefix doesn't even need to be shown
be shown to end users. to end users.
2.5. Examples 2.5. Examples
Example 1: [[anchor8: Barry: This example looks wrong: the "envelope" test is
require ["extlists"]; probably not right. Should it really be using the :list test? It's
testing :detail, so I think it should just be a simple test, maybe '
:is "mylist" ' or some such. No? Alexey: I think this test is
correct. This is checking for known plus addresses (parts).]]
Example 1 uses the "envelope" option [Sieve] and the "subaddress"
extension [Subaddress]:
require ["extlists", "envelope", "subaddress"];
# Submission from list members is sent to all members # Submission from list members is sent to all members
if allof (envelope :detail :list "to" if allof (envelope :detail :list "to"
"tag:example.com,2009-05-28:mylist", "tag:example.com,2009-05-28:mylist",
header :contains :list "from" header :list "from"
"tag:example.com,2009-05-28:mylist") { "tag:example.com,2009-05-28:mylist") {
redirect :list "tag:example.com,2009-05-28:mylist"; redirect :list "tag:example.com,2009-05-28:mylist";
} }
3. Security Considerations 3. Security Considerations
Security considerations related to the "envelope"/"header" tests and Security considerations related to the "address"/"envelope"/"header"
"redirect" action discussed in [Sieve] also apply to this document. tests and "redirect" action discussed in [Sieve] also apply to this
document.
A failure to retrieve data due to the server storing the external A failure to retrieve data due to the server storing the external
list membership being down or otherwise inaccessible may alter the list membership being down or otherwise inaccessible may alter the
result of Sieve processing. So implementations SHOULD treat a result of Sieve processing. Implementations SHOULD treat a temporary
temporary failure to retrieve or verify external list membership in failure to retrieve or verify external list membership in the same
the same manner as a temporary failure to retrieve a Sieve script. manner as a temporary failure to retrieve a Sieve script. For
For example, if the Sieve script is stored in the Lightweight example, if the Sieve script is stored in the Lightweight Directory
Directory Access Protocol (LDAP) and the script can't be retrieved Access Protocol [LDAP] and the script can't be retrieved when a
when a message is processed, then the agent performing Sieve message is processed, then the agent performing Sieve processing can
processing can, for example, assume that the script doesn't exist or either assume that the script doesn't exist or delay message delivery
delay message delivery until the script can be retrieved until the script can be retrieved successfully. External list
successfully. External list memberships should be treated as if they memberships should be treated as if they are a part of the script
are a part of the script itself, so a temporary failure to retrieve itself, so a temporary failure to retrieve or query them should be
them should be handled in the same way as a temporary failure to handled in the same way as a temporary failure to retrieve the Sieve
retrieve the Sieve script itself. script itself.
Protocols/APIs used to retrieve/verify external list membership MUST Protocols/APIs used to retrieve/verify external list membership MUST
provide at least the same level of confidentiality as protocols/APIs provide an appropriate level of confidentiality and authentication.
used to retrieve Sieve scripts. For example, if Sieve scripts are Usually, that will be at least the same level of confidentiality as
retrieved using LDAP secured with Transport Layer Security (TLS) protocols/APIs used to retrieve Sieve scripts, but only the
encryption, then the protocol used to retrieve external list implementation (or deployment) will know what is appropriate.
membership must use a comparable mechanism for providing connection There's a difference, for example, between making an LDAP request on
confidentiality. In particular, the protocol used to retrieve a closed LAN that's only used for trusted servers (it may be that
external list membership must not be lacking encryption. neither encryption nor authentication is needed), on a firewalled LAN
internal to a company (it might be OK to skip encryption, depending
upon policy), and on the open Internet (encryption and authentication
are probably both required). It also matters whether the list being
accessed is private or public (no encryption or authentication may be
needed for public data, even on the Internet).
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 features that can be used to
minimize network traffic and load on the directory service. For minimize network traffic and load on the directory service. For
example LDAP allows for search filters. example, LDAP allows for search filters. Implementations SHOULD use
such features whenever they can.
Many organizations support external lists with thousands of Many organizations support external lists with thousands of
recipients. In order to avoid mailbombs, when redirecting a message recipients. In order to avoid mailbombs when redirecting a message
to an externally stored mailing list, implementations SHOULD enforce to an externally stored list, implementations SHOULD enforce limits
limits on the number of recipients and/or on domains to which such 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
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[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-ietf-vcarddav-carddav, July 2009.
[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.
[Subaddress]
Murchison, K., "Sieve Email Filtering: Subaddress
Extension", RFC 5233, January 2008.
[TAG-URI] Kindberg, T. and S. Hawke, "The 'tag' URI Scheme", [TAG-URI] Kindberg, T. and S. Hawke, "The 'tag' URI Scheme",
RFC 4151, October 2005. RFC 4151, October 2005.
Author's Address Authors' Addresses
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
Barry Leiba
Huawei Technologies
USA
Phone: +1 646 827 0648
Email: barryleiba@computer.org
URI: http://internetmessagingtechnology.org/
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