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Network Working Group                                           N. FreedRequest for Comments: 5183                              Sun MicrosystemsCategory: Standards Track                                       May 2008Sieve Email Filtering: Environment ExtensionStatus of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Abstract   This document describes the "environment" extension to the Sieve   email filtering language.  The "environment" extension gives a Sieve   script access to information about the Sieve interpreter itself,   where it is running, and about any transport connection currently   involved in transferring the message.1.  Introduction   Sieve [RFC5228] is a language for filtering email messages at or   around the time of final delivery.  It is designed to be   implementable on either a mail client or mail server.  It is suitable   for running on a mail server where users may not be allowed to   execute arbitrary programs, such as on black box Internet Message   Access Protocol [RFC3501] servers, as it has no user-controlled loops   or the ability to run external programs.   Although Sieve is intended to be independent of access protocol, mail   architecture, and operating system, in some cases it is useful to   allow scripts to access information about their execution context.   The "environment" extension provides a new environment test that can   be used to implement scripts that behave differently when moved from   one system to another, when messages arrive from different remote   sources or when otherwise operated in different contexts.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 [RFC2119].Freed                       Standards Track                     [Page 1]

RFC 5183              Sieve Environment Extension               May 2008   The terms used to describe the various components of the Sieve   language are taken fromSection 1.1 of [RFC5228].   This document refers to the ABNF productions IPv4-address-literal,   IPv6-address-literal, and General-address-literal defined inSection4.1.3 of [RFC2821].   The location item makes use of standard terms for email service   components.  Additional information and background on these terms can   be found in [EMAIL-ARCH].3.  Capability Identifiers   The capability string associated with the extension defined in this   document is "environment".4.  Environment Test   Usage:   environment [COMPARATOR] [MATCH-TYPE]                        <name: string>                        <key-list: string-list>   The environment test retrieves the item of environment information   specified by the name string and matches it to the values specified   in the key-list argument.  The test succeeds if a match occurs.  The   type of match defaults to ":is" and the default comparator is   "i;ascii-casemap".   The current message is not a direct source of information for the   environment test; the item of information specified by the name   string is extracted from the script's operating environment and the   key-list argument comes from the script.   The environment test MUST fail unconditionally if the specified   information item does not exist.  A script MUST NOT fail with an   error if the item does not exist.  This allows scripts to be written   that handle nonexistent items gracefully.  In particular, the test:     if environment :contains "item" "" { ... }   only succeeds if "item" is known to the implementation, and always   succeeds if it is.   The "relational" extension [RFC5231] adds a match type called   ":count".  The count of an environment test is 0 if the environment   information returned is the empty string, or 1 otherwise.Freed                       Standards Track                     [Page 2]

RFC 5183              Sieve Environment Extension               May 2008   Environment items can be standardized or vendor-defined.  An IANA   registry is defined for both types of items.  Extensions designed for   interoperable use SHOULD be defined in standards track or   experimental RFCs.4.1.  Initial Standard Environment Items   The initial set of standardized environment items is as follows:    "domain"  => The primary DNS domain associated with the Sieve                 execution context, usually but not always a proper                 suffix of the host name.    "host"    => The fully-qualified domain name of the host where                 the Sieve script is executing.    "location"              => Sieve evaluation can be performed at various                 different points as messages are processed.  This item                 provides additional information about the type of                 service that is evaluating the script.  Possible values                 are "MTA", meaning the Sieve is being evaluated by a                 Message Transfer Agent, "MDA", meaning evaluation is                 being performed by a Mail Delivery Agent, "MUA",                 meaning evaluation is being performed by a Mail User                 Agent, and "MS", meaning evaluation is being performed                 by a Message Store.  Additional information and                 background on these terms can be found in                 [EMAIL-ARCH].    "name"    => The product name associated with the Sieve interpreter.    "phase"   => The point relative to final delivery where the                 Sieve script is being evaluated.  Possible values are                 "pre", "during", and "post", referring respectively to                 processing before, during, and after final delivery                 has taken place.    "remote-host"              => Host name of remote SMTP/LMTP/Submission client                 expressed as a Fully Qualified Domain Name (FQDN),                 if applicable and available.  The empty string will be                 returned if for some reason this information cannot be                 obtained for the current client.Freed                       Standards Track                     [Page 3]

RFC 5183              Sieve Environment Extension               May 2008    "remote-ip"              => IP address of remote SMTP/LMTP/Submission client, if                 applicable and available.  IPv4, IPv6, and other types                 of addresses are respectively represented in the                 formats defined by the IPv4-address-literal,                 IPv6-address-literal, and General-address-literal                 productions defined inSection 4.1.3 of [RFC2821].    "version" => The product version associated with the Sieve                 interpreter.  The meaning of the product version string                 is product-specific and should always be considered                 in the context of the product name given by the                 "name" item.   Implementations SHOULD support as many of the items on this initial   list as possible.  Additional standardized items can only be defined   in standards-track or experimental RFCs.4.2.  Vendor-defined Environment Items   Environment item names beginning with "vnd." represent vendor-defined   extensions.  Such extensions are not defined by Internet standards or   RFCs, but are still registered with IANA in order to prevent   conflicts.4.3.  IANA Registration of Environment Items   A registry of environment items is provided by IANA.  Item names may   be registered on a first-come, first-served basis.   Groups of items defined in a standards track or experimental RFC MAY   choose to use a common name prefix of the form "name.", where "name"   is a string that identifies the group of related items.   Items not defined in a standards track or experimental RFC MUST have   a name that begins with the "vnd." prefix, and this prefix is   followed by the name of the vendor or product, such as   "vnd.acme.rocket-sled-status".Freed                       Standards Track                     [Page 4]

RFC 5183              Sieve Environment Extension               May 20084.3.1.  Template for Environment Registrations   The following template is to be used for registering new Sieve   environment item names with IANA.      To: iana@iana.org      Subject: Registration of new Sieve environment item      Item name: [the string for use in the 'environment' test]      Description:     [a brief description of the semantics of the                        value the item returns]      RFC number:      [for extensions published as RFCs]      Contact address: [email and/or physical address to contact for                        additional information]   Multiple items and descriptions MAY be specified in a single   registration request.  Both standardized and vendor-defined items use   this form.5.  Security Considerations   The environment extension may be used to obtain information about the   system the Sieve implementation is running on.  This information in   turn may reveal details about service provider or enterprise   infrastructure.   An implementation can use any technique to determine the remote-host   environment item defined in this specification, and the   trustworthiness of the result will vary.  One common method will be   to perform a PTR DNS lookup on the client IP address.  This   information may come from an untrusted source.  For example, the   test:     if environment :matches "remote-host" "*.example.com" { ... }   is not a good way to test whether the message came from "outside"   because anyone who can create a PTR record can create one that refers   to whatever domain they choose.   All of the security considerations given in the base Sieve   specification also apply to this extension.Freed                       Standards Track                     [Page 5]

RFC 5183              Sieve Environment Extension               May 20086.  IANA Considerations   The following template specifies the IANA registration of the Sieve   extension specified in this document:      To: iana@iana.org      Subject: Registration of new Sieve extension      Capability name: environment      Description:     The "environment" extension provides a new                       environment test that can be used to implement                       scripts that behave differently when moved                       from one system to another or otherwise                       operated in different contexts.      RFC number:RFC 5183      Contact address: Sieve discussion list <ietf-mta-filters@imc.org>   This specification also defines a new IANA registry for Sieve   environment item names.  The specifics of this registry are given inSection 4.3.  The initial contents of the registry are given in the   following section.Freed                       Standards Track                     [Page 6]

RFC 5183              Sieve Environment Extension               May 20086.1.  Initial Environment Item Registrations   The following template specifies the initial IANA registrations for   the environment items defined in this document:      To: iana@iana.org      Subject: Registration of new Sieve environment items      Capability name: domain      Description:     The primary DNS domain associated with the Sieve                       execution context, usually but not always a                       proper suffix of the host name.      Capability name: host      Description:     The fully-qualified domain name of the host                       where the Sieve script is executing.      Capability name: location      Description:     Type of service executing the Sieve script.      Capability name: name      Description:     The product name associated with the Sieve                       interpreter.      Capability name: phase      Description:     Point relative to final delivery at which the                       Sieve script is being evaluated.      Capability name: remote-host      Description:     Host name of remote SMTP client, if applicable                       and available.      Capability name: remote-ip      Description:     IP address of remote SMTP client, if applicable                       and available.      Capability name: version      Description:     The product version associated with the Sieve                       interpreter.      RFC number:RFC 5183      Contact address: Sieve discussion list <ietf-mta-filters@imc.org>Freed                       Standards Track                     [Page 7]

RFC 5183              Sieve Environment Extension               May 20087.  References7.1.  Normative references   [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate                 Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2821]     Klensin, J., "Simple Mail Transfer Protocol",RFC 2821,                 April 2001.   [RFC5228]     Guenther, P. and T. Showalter, "Sieve: An Email                 Filtering Language",RFC 5228, January 2008.   [RFC5231]     Segmuller, W. and B. Leiba, "Sieve Email Filtering:                 Relational Extension",RFC 5231, January 2008.7.2.  Informative references   [EMAIL-ARCH]  Crocker, D.,"Internet Mail Architecture", Work                 in Progress, February 2008.   [RFC3501]     Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL -                 VERSION 4rev1",RFC 3501, March 2003.Freed                       Standards Track                     [Page 8]

RFC 5183              Sieve Environment Extension               May 2008Appendix A.  Acknowledgements   Brian Carpenter, Dave Crocker, Cyrus Daboo, Philip Guenther, Kjetil   Torgrim Homme, John Klensin, Mark Mallett, Alexey Melnikov, and   Dilyan Palauzo provided helpful suggestions and corrections.Author's Address   Ned Freed   Sun Microsystems   3401 Centrelake Drive, Suite 410   Ontario, CA  92761-1205   USA   Phone: +1 909 457 4293   EMail: ned.freed@mrochek.comFreed                       Standards Track                     [Page 9]

RFC 5183              Sieve Environment Extension               May 2008Full Copyright Statement   Copyright (C) The IETF Trust (2008).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 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 athttp://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.Freed                       Standards Track                    [Page 10]