Sieve Working Group A. Melnikov Internet-Draft Isode Limited Intended status: Standards Track July 6, 2007 Expires: January 7, 2008 Sieve Extension: Externally Stored Lists draft-melnikov-sieve-external-lists-01 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 7, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract Sieve scripting language can be used for implementing of whitelisting, blacklisting and personal distribution lists. Currently this requires that all members of such lists be hardcoded 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 mail server. This document defines a Sieve extension for accessing externally Melnikov Expires January 7, 2008 [Page 1] Internet-Draft Sieve Extension: Externally Stored Lists July 2007 stored mailing lists, i.e. list whose members are stored externally to the script, for example in LDAP (RFC 4510), ACAP (RFC 2244) or a relational database. ToDo o Need a way to advertise supported URI schemas in ManageSieve and ihave. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . . . 3 2. Extlists extension . . . . . . . . . . . . . . . . . . . . . 3 2.1. Capability Identifier . . . . . . . . . . . . . . . . . . . . 3 2.2. :list tagged argument to the 'address', 'header' and 'envelope' tests . . . . . . . . . . . . . . . . . . . . . . 3 2.3. :list tagged argument to the 'redirect' action . . . . . . . 4 2.4. Syntax of an externally stored list name . . . . . . . . . . 4 2.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Security Considerations . . . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.1. Normative References . . . . . . . . . . . . . . . . . . . . 6 6.2. Informative References . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . 6 Intellectual Property and Copyright Statements . . . . . . . 7 Melnikov Expires January 7, 2008 [Page 2] Internet-Draft Sieve Extension: Externally Stored Lists July 2007 1. Introduction This document specified an extension to the Sieve language defined by [Sieve] for checking membership in an externally stored list or for sending messages to a list of recipients stored externally to the Sieve script. This extension adds a new tagged argument to the "header" and "envelope" tests, and to the "redirect" action [Sieve]. 1.1. Conventions used in this document Conventions for notations are as in [Sieve] section 1.1, including the use of [ABNF]. 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 [Kwds]. 2. Extlists extension 2.1. Capability Identifier The capability string associated with the extension defined in this document is "extlists". 2.2. :list tagged argument to the 'address', 'header' and 'envelope' tests Usage: address [COMPARATOR] [ADDRESS-PART] [MATCH-TYPE] [:list] Usage: header [COMPARATOR] [MATCH-TYPE] [:list] Usage: envelope [COMPARATOR] [ADDRESS-PART] [MATCH-TYPE] [:list] The new ":list" tagged argument, if present, changes interpretation of the "key-list" parameter to the 'address'/'header'/'envelope' test to become a list of names of externally stored lists. E.g. the "header" test with the ":list" parameter evaluates to true if the value of any of the named headers, ignoring leading and trailing whitespace, matches any member of one or more externally stored lists Melnikov Expires January 7, 2008 [Page 3] Internet-Draft Sieve Extension: Externally Stored Lists July 2007 of values with names specified in key-list. See Section 2.4 for the detailed description of syntax used for naming externally stored lists. 2.3. :list tagged argument to the 'redirect' action Usage: redirect :list The "redirect" action with the ":list" argument is used to send the message to one or more email address stored in the externally stored list 'ext-list-name'. This variant of the redirect command can be used to implement a personal distribution list. See Section 2.4 for the detailed description of syntax used for naming externally stored lists. 2.4. Syntax of an externally stored list name [[anchor5: Specify ABNF. Dave Cridland has suggested to use a leading ':' for "opaque" identifiers.]] A name of an externally stored list is either an absolute URL (e.g. an [LDAP], [ACAP] or [CardDAV] URL) or an opaque identifier. Interpretation of opaque identifiers is left up to implementations. They can hide complexity of an implementation from end users. For example, an implementation can provide a web interface for managing lists of users stored in LDAP. Requiring users to know syntax for LDAP URLs is just not very practical. 2.5. Examples Example 1: require ["extlists"]; # Submission from list members is sent to all members if allof (envelope :detail :list "to" "mylist", header :contains :list "from" "mylist") { redirect :list "mylist"; } 3. Security Considerations Security considerations are discussed in [Sieve]. [[anchor6: Describe risks of external lists including thousands of Melnikov Expires January 7, 2008 [Page 4] Internet-Draft Sieve Extension: Externally Stored Lists July 2007 recipients.]] [[anchor7: Describe how to handle outages of servers providing access to an externally stored list.]] Implementations of this extensions should keep in mind that matching 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 to servers providing access to externally stored mailing lists. A naive implementation, such as the one that tries to retrieve content of the whole list to perform matching can make this worse. But note that many protocols that can be used for accessing externally stored lists support flexible searching facilities that can be used to minimize network traffic. For example LDAP allows for search filters. In order to avoid mailbombs, when redirecting a message to an externally stored mailing list, implementations SHOULD enforce limits on the number of recipients and/or on domains to which such recipients belong. 4. IANA Considerations The following template specifies the IANA registration of the notify Sieve extension specified in this document: To: iana@iana.org Subject: Registration of new Sieve extension Capability name: extlists Description: adds the ':list' tagged argument to 'address', 'header' and 'envelope' tests, and to the 'redirect' action. The ':list' argument changes address/header/envelope test to match values against values stored in one or more externally stored list. The ':list' argument to the redirect action changes the redirect action to forward the message to email addresses stored in the externally stored list. RFC number: this RFC Contact address: The Sieve discussion list This information should be added to the list of sieve extensions given on http://www.iana.org/assignments/sieve-extensions. 5. Acknowledgements Thanks to Alexandros Vellis, Barry Leiba, Nigel Swinson, Kjetil Torgrim Homme, Dave Cridland, Cyrus Daboo, Pete Resnick for ideas, comments and suggestions. Melnikov Expires January 7, 2008 [Page 5] Internet-Draft Sieve Extension: Externally Stored Lists July 2007 6. References 6.1. Normative References [ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 4234, October 2005. [Kwds] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [Sieve] Guenther, P. and T. Showalter, "Sieve: An Email Filtering Language", work in progress, draft-ietf-sieve-3028bis, August 2006. [URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. 6.2. Informative References [ACAP] Newman, C. and J. Myers, "ACAP -- Application Configuration Access Protocol", RFC 2244, November 1997. [CardDAV] Daboo, C., "vCard Extensions to WebDAV (CardDAV)", work in progress, draft-daboo-carddav, May 2007. [LDAP] Zeilenga, K., "Lightweight Directory Access Protocol (LDAP): Technical Specification Road Map", RFC 4510, June 2006. Author's Address Alexey Melnikov Isode Limited 5 Castle Business Village 36 Station Road Hampton, Middlesex TW12 2BX UK Email: Alexey.Melnikov@isode.com Melnikov Expires January 7, 2008 [Page 6] Internet-Draft Sieve Extension: Externally Stored Lists July 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Melnikov Expires January 7, 2008 [Page 7]