Internet Engineering Task Force T. Hansen Internet-Draft AT&T Laboratories Intended status: Standards Track C. Daboo Expires:January 9,August 26, 2008 AppleComputer July 8, 2007Inc. February 23, 2008 Sieve Email Filtering: MIME part Tests, Iteration, Extraction, Replacement and Enclosuredraft-ietf-sieve-mime-loop-03draft-ietf-sieve-mime-loop-04 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 onJanuary 9,August 26, 2008. Copyright Notice Copyright (C) The IETF Trust(2007).(2008). AbstractTheThis document defines extensions to the Sieve email filtering languagehas no waytoexamine individualpermit analysis and manipulation of the MIME body partsor any way to manipulate those individual parts. However, being able to filter based on MIME content is important. This document defines extensions for these needs.of an email message. Note This document is being discussed on the MTA-FILTERS mailing list, ietf-mta-filters@imc.org. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 3. Sieve Loops . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Changes to Sieve tests . . . . . . . . . . . . . . . . . . . . 4 4.1. Test "header" . . . . . . . . . . . . . . . . . . . . . . 4 4.2. Test "address" . . . . . . . . . . . . . . . . . . . . . . 6 4.3. Test "exists" . . . . . . . . . . . . . . . . . . . . . . 7 5. Action Replace . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Action Enclose . . . . . . . . . . . . . . . . . . . . . . . . 8 7. Action extract_text . . . . . . . . . . . . . . . . . . . . . 9 8. Sieve Capability Strings . . . . . . . . . . . . . . . . . . . 9 9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 9.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 10 9.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 10 9.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . . . 11 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 11. Security Considerations . . . . . . . . . . . . . . . . . . . 12 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 12.1. for_every_part capability . . . . . . . . . . . . . . . . 13 12.2. mime capability . . . . . . . . . . . . . . . . . . . . . 13 12.3. replace capability . . . . . . . . . . . . . . . . . . . . 14 12.4. enclose capability . . . . . . . . . . . . . . . . . . . . 14 12.5. extract_text capability . . . . . . . . . . . . . . . . . 14 13. Change History (to be removed prior to publication as an RFC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1315 13.1. draft-ietf-sieve-mime-02 . . . . . . . . . . . . . . . . .1415 13.2. draft-ietf-sieve-mime-01 . . . . . . . . . . . . . . . . .1415 13.3. draft-ietf-sieve-mime-00 . . . . . . . . . . . . . . . . .1415 13.4. draft-hansen-sieve-loop-01 . . . . . . . . . . . . . . . .1416 13.5. draft-hansen-sieve-loop-02 . . . . . . . . . . . . . . . .1416 13.6. draft-hansen-sieve-loop-03 . . . . . . . . . . . . . . . .1516 13.7. draft-sieve-mime-loop-04 . . . . . . . . . . . . . . . . . 16 14. References . . . . . . . . . . . . . . . . . . . . . . . . . .1517 14.1. Normative References . . . . . . . . . . . . . . . . . . .1517 14.2. Informative References . . . . . . . . . . . . . . . . . .1617 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .1617 Intellectual Property and Copyright Statements . . . . . . . . . .1719 1. IntroductionSieve scripts are used to make decisions about the disposition of an email message. The base Sieve specification, [I-D.ietf-sieve-3028bis], defines operators for looking at the message headers, such as addresses and the subject. Other extensions provide access to the body of the message ([I-D.ietf-sieve-body]), or allow you to manipulate the header of the message ([I-D.ietf-sieve-editheader]). But none of these extensions take into account thatMIME messages ([RFC2045]) are often complex objects, consisting of many parts and sub-parts. This extension defines mechanisms for performing tests on MIME body parts, looping through the MIME body parts, extracting information from a MIME body part, changing the contents of a MIME body part, and enclosing the entire messagewithwithin a wrapper. 2. Conventions Used in This Document Conventions for notations are as in[I-D.ietf-sieve-3028bis][RFC5228] section 1.1. 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]. 3. Sieve Loops The base Sieve language has no looping mechanism. Given that messages may contain multiple parts, in order to support filters that apply to any and all parts, we introduce a new control command: "for_every_part", which is an iterator that walks though every MIME part of a message, including nested parts, depth first, and applies the commands in the specified block to each of them. The iterator will start with the first MIME part (as its current context) and will execute a command block (Sieve commands enclosed by{ ...}).{...}). Upon completion of this command block, the iterator advances to the next MIME part (as its current context) and executes the same command block again. The iterator can be terminated prematurely by a new Sieve command, "break". Usage: for_every_part block Usage: break; "for_every_part" commands can be nested inside other "for_every_part" commands. When this occurs, the nested "for_every_part" iterates over the MIME parts contained within the MIME partcurrentcurrently being targeted by the nearest enclosing "for_every_part" command. If that MIME part is a terminal MIME part (i.e. does not contain other MIME parts) then the nested "for_every_loop" is simply ignored. Sieve implementations MAY limit the number of nested loops that occur within one another, however they MUST support at least one nested loop inside another loop. 4. Changes to Sieve tests This specification extends the base Sieve "header", "address" and "exists" tests to support targeting those tests at a specific MIME part or at all MIME parts in the enclosing scope. 4.1. Test "header" The "header" test is extended with the addition of a new ":mime" taggedargument, which takes a number of other arguments.argument and its associated options. Usage: header [:mime] [:anychild] [MIMEOPTS] [COMPARATOR] [MATCH-TYPE] <header-names: string-list> <key-list: string-list> Usage: The definition of [MIMEOPTS] is: Syntax: ":type" / ":subtype" / ":contenttype" / ":param" <param-list: string-list> When the ":mime" tagged argument is present in the "header" test, it will parse the MIME header lines inathe message so that tests can be performed on specific elements.If theWhen used outside the context of a "for_every_part" iterator, and without an ":anychild" taggedargument is NOT specified: o Ifargument, the "header" test will examine only the outer top-level RFC2822 headers of the message. When usedwithininside the context of a "for_every_part" iterator, and without an ":anychild" tagged argument, the "header" test will examine the headers associated with the current MIME part context from the loop.o IfWhen used outside the context of a "for_every_part" iterator, and with an ":anychild" tagged argument, the "header" test will examineonly the outer, top-level, headersall MIME body parts and return true if any of them satisfies themessage. Iftest. When used inside the context of a "for_every_part" iterator, and with an ":anychild" taggedargument IS specified,argument, the "header" test will examine the current MIME part context and all it's nested MIME bodyparts and returnparts, returning true if any of them satisfies the test. The "header" test with the ":mime" tagged argument can test various aspects of certainstructedstructured MIME headers. These options are available: :type parses the header assuming it has the format of a "Content- Type:" MIME header field, and tests the value of the MIME type specified in the header. :subtype parses the header assuming it has the format of a "Content- Type:" MIME header field, and tests the value of the MIME subtype specified in the header. :contenttype parses the header assuming it has the format of a "Content-Type:" MIME header field, and tests the combined value of the MIME type and subtype specified in the header. :param parses the header looking for MIME parameters in the header. The supplied string-list lists the names of any parameters to be tested. If any one named parameter value matches the test string value, the test will return true. Example: require ["mime", "fileinto"]; if header :mime :type "Content-Type" "image" { fileinto "INBOX.images"; } In this example, any message that contains a MIME image type part at the top-level is saved to the mailbox "INBOX.images". Example: require ["mime", "fileinto"]; if header :mime :anychild :contenttype:comparator"Content-Type" "text/html" { fileinto "INBOX.html"; } In this example, any message that contains any MIME part with a content-type of "text/html" is saved to the mailbox "INBOX.html". Example: require ["mime", "for_every_part", "fileinto"]; for_every_part { if allof ( header :mime :param "filename":comparator:contains "Content-Disposition""important""important", header :mime :subtype "Content-Type" "pdf", size :over "100K") { fileinto "INBOX.important"; break; } } In this example, any message that containsanya MIME partwiththat has a content-disposition with a filename parameter containing the text"important""important", has a content-subtype of "pdf" and is bigger than 100 Kb is saved to the mailbox "INBOX.important". 4.2. Test "address" The "address" test is extended with the addition of a new ":mime" tagged argument, which takes a number of other arguments. Usage: address [:mime] [:anychild] [COMPARATOR] [ADDRESS-PART] [MATCH-TYPE] <header-list: string-list> <key-list: string-list> When the ":mime" tagged argument is present in the "address" test, it will parse the MIME header lines as if they were standard address header lines in a message so that tests can be performed on specific elements. The behavior of the ":anychild" tagged argument and the interaction with the "for_every_part" iterator is the same as for the extended "header" test Section 4.1. Example: require ["mime", "fileinto"]; if address :mime :is :all "content-from" "tim@example.com" { fileinto "INBOX.part-from-tim"; } In this example, any message that contains a MIME Content-From header at the top-level matching the text "tim@example.com" is saved to the mailbox "INBOX.part-from-time". 4.3. Test "exists" The "exists" test is extended with the addition of a new ":mime" tagged argument, which takes one other argument. Usage: exists [:mime] [:anychild] <header-names: string-list> When the ":mime" tagged argument is present in the "exists" test, the test is extended to check for the existence of MIME headers in MIME parts. The behavior of the ":anychild" tagged argument and the interaction with the "for_every_part" iterator is the same as for the extended "header" test Section 4.1. Example: require ["mime", "fileinto"]; if exists :mime :anychild "content-md5" { fileinto "INBOX.md5"; } In this example, any message that contains a MIME Content-MD5 header in any MIME part is saved to the mailbox "INBOX.md5". 5. Action Replace Usage: replace [:mime] [:subject string] [:from string] <replacement: string> The "replace" command is defined to allow a MIME part to be replaced with the text supplied in the command. When used in the context of a "for_every_part" iterator, the MIME part to be replaced is the "current" MIME part. If the current MIME context is a multipart MIME part, the entire multipart MIME part is replaced, which would alter the MIME structure of the message by eliminating all of the children of the multipart part. (Replacing a non-multipart MIME part within a "for_every_part" loop context does not alter the overall message structure.) If the MIME structure is altered, the change takes effect immediately: the "for_every_part" iterator that is executing does not go into the no-longer existing body parts, and subsequent "for_every_part" iterators would use the new message structure. When used outside the context of a "for_every_part" loop, the MIME part to be replaced is the entire message. If the :mime parameter is not specified, the replacement string is a text/plainpart.part in UTF-8. If the :mime parameter is specified, then the replacement string is, in fact, a MIME entity as defined in [RFC2045] section 2.4, including both MIME headers and content. If theoptional :mime parameter is not supplied, the reason string is considered to be a UTF-8 string. If theentire message is being replaced, a ":subject" parameter specifies a subject line to attach to the message that is generated. UTF-8 characters can be used in the string argument; implementations MUST convert the string to [RFC2047] encoded words if and only if non-ASCII characters are present. Implementations MUST preserve the previous Subject header as an Original-Subject header. If the entire message is being replaced, a ":from" parameter may be used to specify an alternate address to use in the From field of the message that is generated. The string must specify a valid [RFC2822] mailbox-list. Implementations SHOULD check the syntax and generate an error when a syntactically invalid ":from" parameter is specified. Implementations MAY also impose restrictions on what addresses can be specified in a ":from" parameter; it is suggested that values that fail such a validity check simply be ignored rather than causing the replace action to fail. Implementations MUST preserve the previous From header as an Original-From header. 6. Action Enclose Usage: enclose <:subject string> <:headers string-list> string A new Sieve action command is defined to allow an entire message to be enclosed as an attachment to a new message. After enclosure, subsequent actions affecting the message header or content use the newlycreatecreated message instead of the original message; this means that any use of a "replace" action or other similar actions should be executed before the "enclose" action. If multiple "enclose" actions are executed by a script, only the text specified on the last one is used when creating the enclosed message. This action does not affect messages that are forwarded via a "redirect" action. Specifically, the original message becomes a multipart/mixed message with two parts: a text/plain portion with the string argument as its body, and a message/rfc822 portion with the original message enclosed. The Content-Type: header field becomes multipart/mixed. The Subject: header is specified by the :subject argument. Any headers specified by :headers are copied from the old message into the new message. If not specified by :headers, Date: and From: headers should be synthesized to reflect the current date and the user running the Sieve action. 7. Action extract_text Usage: extract_text [MODIFIER] [":first" number] <varname: string> The extract_text action may be used within the context of a "for_every_part" loop. Servers MUST support transcoding of any textual body part into UTF-8 for use with this action. This requires decoding any transfer encoding as well as transcoding from the indicated character set into UTF-8. It stores at most :firstbytescharacters of the transcoded content of the current MIME body part in the variable identified by varname. If the :first parameter is not present, the whole content of the current MIME body part is stored. In either case the actually stored data MAY be truncated to conform toimplementation specificimplementation-specific limit on variable length and/or on MIME body part length.QUESTION: What do we do ifIf theContent-Transfer-Encodingtransfer encoding or character set isanything other than 7bit?unrecognized by the implementation or recognized but invalid, an empty string will result. If extract_text is used outside the context of a "for_every_part" loop, the action will set the variable identified by varname to the empty string. Modifiers are applied on the extracted text before it is stored in the variable. See[I-D.ietf-sieve-variables][RFC5229] for details. 8. Sieve Capability Strings A Sieve implementation that defines the "for_every_part" and "break" actions will advertise the capability string "for_every_part". A Sieve implementation that defines the ":mime" and ":anychild" tagged arguments to the "header", "address" and "exists"commandstests will advertise the capability string "mime". A Sieve implementation that defines the "replace" action will advertise the capability string "replace". A Sieve implementation that defines the "enclose" action will advertise the capability string "enclose". A Sieve implementation that defines the "extract_text" action will advertise the capability string "extract_text". Note that to be useful, the "extract_text" action also requires the "variables"[I-D.ietf-sieve-variables][RFC5229] and"mime""for_every_part" capabilities. 9. Examples 9.1. Example 1 A Sieve script to replace all the Windows executable attachments in a message would be: require [ "for_every_part", "mime", "replace" ]; for_every_part { if(anyof ( header :mime :contenttype :is "Content-Type" "application/exe", header :mime :param "filename" ["Content-Type", "Content-Disposition"] :matches "*.com" ) { replace "Executable attachment removed by user filter"; } } 9.2. Example 2 A Sieve script to warn the user about executable attachment types would be: require [ "for_every_part", "mime", "enclose" ]; for_every_part { if header :mime :param "filename" ["Content-Type", "Content-Disposition"] :matches ["*.com", "*.exe", "*.vbs", "*.scr", "*.pif", "*.hta", "*.bat", "*.zip" ] { # these attachment types are executable enclose :subject "Warning"":text WARNING! The enclosed message contains executable attachments. These attachments types may contain a computer virus program that can infect your computer andpotententlypotentially damage yourdatadata. Before clicking on these message attachments, you should verify with the sender that this message was sent by them and not a computer virus.";. break; } } 9.3. Example 3 A Sieve script to extract subject and text out of messages from thebossboss: require ["mime", "variables", "extract_text"]; if header :contains "from" "boss@example.org" { # :matches is used to get the value of the Subject header if header :matches "Subject" "*" { set "subject" "${1}"; } # extract the first 100bytescharacters of the first text/* part for_every_part { if header :mime :type :is "Content-Type" "text" { extract_text :first 100 "msgcontent"; break; } } # if it's not a 'for your information' message if not header :contains "subject" "FYI:" { # do something using ${subject} and ${msgcontent} # such as sending a notification using a # notificationextionextensions } } 10. Acknowledgements Comments from members of the MTA Filters Working Group, in particular Ned Freed,Nigel Swinson,Kjetil Torgrim Homme, MarkMallett andMallett, Alexey Melnikov, Aaron Stone and Nigel Swinson are gratefully acknowledged. 11. Security Considerations The "enclose" action creates an entirely new message, as compared to just redirecting or forwarding the existing message. Therefore, any site policies applicable to message submission should beenforced here.enforced. The looping specification specified here provides easier access to information about the message contents, which may also be achieved through other sieve tests. This is not believed to raise any additional security issues beyond those for the Sieve "envelope" and "body" [I-D.ietf-sieve-body] tests. The system MUST be sized and restricted in such a manner that even malicious use of mime part matching does not deny service to other users of the host system. Any change in a message content may interfere with digital signature mechanisms that include the body in the signed material. All of the security considerations given in the base Sieve specification also apply to these extensions. 12. IANA Considerations The Original-Subject: and Original-From: headers are to be registered in the Permanent Message Header Fields table. The followingtemplate specifiestemplates specify the IANAregistrationregistrations of the Sieve extensions specified in thisdocument:document. This information should be added to the list of sieve extensions given on http://www.iana.org/assignments/sieve-extensions. 12.1. for_every_part capability To: iana@iana.org Subject: Registration of new Sieveextensionsextension Capability name: for_every_part Description: adds the "for_every_part" and "break" actions for iterating through MIME parts of a message. RFC number: This RFC Contact address: The Sieve discussion list <ietf-mta-filters@imc.org>. 12.2. mime capability To: iana@iana.org Subject: Registration of new Sieve extension Capability name: mime Description: adds the ":mime" and ":anychild" tagged arguments to the "header", "address" and "exists"commands.tests. RFC number: This RFC Contact address: The Sieve discussion list <ietf-mta-filters@imc.org>. 12.3. replace capability To: iana@iana.org Subject: Registration of new Sieve extension Capability name:replacemime Description: adds the "replace" action for replacing a MIME body part of a message. RFC number: This RFC Contact address: The Sieve discussion list <ietf-mta-filters@imc.org>. 12.4. enclose capability To: iana@iana.org Subject: Registration of new Sieve extension Capability name:enclosemime Description: adds the "enclose" action for enclosing a message with a wrapper. RFC number: This RFC Contact address: The Sieve discussion list <ietf-mta-filters@imc.org>. 12.5. extract_text capability To: iana@iana.org Subject: Registration of new Sieve extension Capability name:extract_textmime Description: adds the "extract_text" action for extracting text from a MIME body part. RFC number: This RFCXXXXContact address: The Sieve discussion list <ietf-mta-filters@imc.org>.This information should be added to the list of sieve extensions given on http://www.iana.org/assignments/sieve-extensions.13. Change History (to be removed prior to publication as an RFC) 13.1. draft-ietf-sieve-mime-02 minor syntax glitches in examples Add clarification on "replace" affecting subsequent for_every_part loops? Add IANA considerations for Original-Subject: and Original-From:. Add note on "enclose" creating From: and Date: headers. 13.2. draft-ietf-sieve-mime-01 what happens when nested for_every_loop's a "mime" shorthand for testing the type/subtype, without requiring interactions with variables notifications notifications to calendar service address tests, exists tests mimeheader, mimeparameter tests 13.3. draft-ietf-sieve-mime-00 Changed title and text to emphasize MIME Tests. Changed for.every.part to for_every_part. Added :anychild to mime test. Default is to use the current context or outer envelope; specifying :anychild will look at all children. Added clarifications to replacing parts affecting the structure. Added :mime option to replace, ala draft-ietf-sieve-vacation-06. Various other minor nit fixes. 13.4. draft-hansen-sieve-loop-01 Merged with draft-daboo-sieve-mime-00.txt. 13.5. draft-hansen-sieve-loop-02 Update to 3028bis reference. Added 2119 conventions section. Terminology/title tweaks. Added informative references to body and editheader extensions. Added description of nested loops. Replaced mime test by extensions to header, address and exists tests. 13.6. draft-hansen-sieve-loop-03 after enclosure, subsequent actions affect newly created message synthesis of Date/From headers by the enclose action is no longer controversial Filled in Security Considerations Picked up extract_text action from draft-ietf-sieve-notify Expanded the IANA considerations section 13.7. draft-sieve-mime-loop-04 update reference for recent published rfcs extract-text now required to do decode transfer encoding and transcode to UTF-8 removed editheader reference since its not actually used several text changes as suggested by Nigel Swinson, including re- writes to abstract and introduction tweaked IANA registrations 14. References 14.1. Normative References[I-D.ietf-sieve-3028bis] Showalter, T. and P. Guenther, "Sieve: An Email Filtering Language", draft-ietf-sieve-3028bis-12 (work in progress), February 2007.[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text", RFC 2047, November 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April 2001. [RFC5228] Guenther, P. and T. Showalter, "Sieve: An Email Filtering Language", RFC 5228, January 2008. 14.2. Informative References [I-D.ietf-sieve-body] Guenther, P. and J. Degener, "Sieve Email Filtering: Body Extension",draft-ietf-sieve-body-06draft-ietf-sieve-body-07 (work in progress),FebruaryDecember 2007.[I-D.ietf-sieve-editheader] Guenther, P. and J. Degener,[RFC5229] Homme, K., "Sieve Email Filtering:EditheaderVariables Extension",draft-ietf-sieve-editheader-08 (work in progress), March 2007. [I-D.ietf-sieve-variables] Homme, K., "Sieve Extension: Variables", draft-ietf-sieve-variables-08 (work in progress), December 2005.RFC 5229, January 2008. Authors' Addresses Tony Hansen AT&T Laboratories 200 Laurel Ave. Middletown, NJ 07748 USA Email: tony+sieveloop@maillennium.att.com Cyrus Daboo AppleComputer,Inc. 1 Infinite Loop Cupertino, CA 95014 USA Email: cyrus@daboo.name URI: http://www.apple.com/ Full Copyright Statement Copyright (C) The IETF Trust(2007).(2008). 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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