Network Working Group Internet Draft: Sieve -- IMAP flag Extension A. Melnikov Document: draft-melnikov-sieve-imapflags-06.txt Isode Limited Expires: July 2004 January 2004 Sieve -- IMAP flag Extension Status of this memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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." To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). The protocol discussed in this document is experimental and subject to change. Persons planning on either implementing or using this protocol are STRONGLY URGED to get in touch with the author before embarking on such a project. Copyright Copyright (C) The Internet Society 2000-2004. All Rights Reserved. Abstract Recent discussions have shown that it is desirable to set different [IMAP] flags on message delivery. This can be done, for example, by a Sieve interpreter that works as a part of a Mail Delivery Agent. This document describes an extension to the Sieve mail filtering language for setting [IMAP] flags. The extension allows to set both [IMAP] system flags and [IMAP] keywords. 0. Meta-information on this draft This information is intended to facilitate discussion. It will be removed when this document leaves the Internet-Draft stage. Editorial comments are marked with << and >>. 0.1. Discussion This draft defines an extension to the Sieve mail filtering language (RFC 3028) being discussed on the MTA Filters mailing list at <ietf-mta-filters@imc.org>. Subscription requests can be sent to <ietf-mta-filters-request@imc.org> (send an email message with the word "subscribe" in the body). More information on the mailing list along with a WWW archive of back messages is available at <http://www.imc.org/ietf-mta-filters/>. 0.2. Open issues 1. There is no way to specify which flags to set on implicit keep. Is this an issue? 2. Do we want to change the extension name, because of incompatible changes with 04 and because 03 was widely deployed? 0.3. Changes from the version submitted to the Sieve mailing list 1. Added addflag and removeflag actions 2. Changed the semantics of setflag (setflag is not additive any more) 3. Corrected section "Interaction with Other Sieve Actions". Removed incorrect reference to the forward action as to an action that prohibits setflag. 4. Added paragraph about the mutual order of "fileinto"/"keep" and "setflag"/"addflag"/"removeflag" actions. 0.4. Changes from the revision 00 1. Corrected Capability Identifier section (Section 2) 2. Corrected "Interaction with Other Sieve Actions" section (Section 4) 3. Examples were updated to be compatible with Sieve-07 draft 4. Added "mark" and "unmark" actions 0.5. Changes from the revision 01 1. Some language fixes based on Tony Hansen comments 2. Clarified that the extension allows to set both IMAP System Flags and Keywords 0.6. Changes from the revision 02 1. BugFix: all backslashes must be escaped 2. Added extended example and more detailed description of "addflag"/"removeflag" additivity. 3. Minor example bugfixes 0.7. Changes from the revision 03 1. Added second way to specify flags to be set (via optional tagged arguments). [Tim Showalter] 2. Rules for using Reject with imapflags relaxed. [Randall Gellens] 3. Removed ABNF section completely, added syntax description to action definition. [Tim Showalter] 4. Cleaned up the example. [Ken Murchison] 5. Added FM (Flag Manupulation) acronym. 6. Clarified "mark"/"unmark" bahavior. [Randall Gellens] 0.8. Changes from the revision 04 1. "Interaction with Other Sieve Actions" was simplified based on comments from Tim Showalter. Added sentence saying that imapflags doesn't change an implicit keep. 2. Several editorial comments from Tim Showalter. 0.9. Changes from the revision 05 1. Updated copyright, author address, section numbers and references. 2. Added dependency on Sieve "variables" extension. 3. Several editorial comments from Matthew Elvey. 4. Removed "mark" and "unmark" actions. 5. Removed "setflag" action. 6. Added "hasflag" test. 7. Dropped ":globalflags" 8. An invalid flag name doesn't cause a script execution failure anymore, as imapflags now depends on variables and a variable can have an arbitrary value. 1. Introduction This is an extension to the Sieve language defined by [SIEVE] for setting [IMAP] flags. It adds a new tagged argument to "keep" and "fileinto" that describes the list of flags that have to be set when the message is delivered to the specified mailbox. It also adds several actions to help manipulate list of flags and a test to check if a flag belongs to a list. This extension depends on the presence of "variables" extension [Variables]. Sieve interpreters that don't support integration with IMAP SHOULD ignore this extension. The capability string associated with extension defined in this document is "imap4flags". <<Extension name has been changed as revision 03 of this document is widely deployed in CMU Cyrus server>> 2. Conventions used. Conventions for notations are as in [SIEVE] section 1.1, including use of [KEYWORDS] and "Syntax:" label for the definition of action and tagged arguments syntax. 2.1. General requirements for flag handling The following notes apply to processing of Addflag and Removeflag actions, hasflag test and :flags tagged argument. A Sieve interpreter MUST ignore empty strings (i.e. "") in a list-of-flags parameter. The Sieve interpreter SHOULD check the list of flags for validity as described by [IMAP] ABNF. In particular non-ASCII characters are not allowed in flag names. However spaces MUST be always allowed and multiple spaces between flag names MUST be treated as a single space character. A string containing a space separated list of flags is equivalent to a string list consisting of the flags. The last requirement is to simplify amalgamation of multiple flag lists. If a flag validity check fails the flag should be silently dropped, but a warning message should be logged by the Sieve interpreter. 3. Actions All actions described in this specification (setflag, addflag, removeflag) operate on string variables that contain a set of [IMAP] flags. On variable substitution a set of flags is represented as a string containing space separated list of flag names. <<Should this cause an automatic duplicate elimination?>> The "addflag" action adds flags to an existing set. The "removeflag" action removes flags from an existing set. The "setflag" action replaces an existing set of flags with a new set. The "set" action defined in [Variables] can be used to replaces an existing set of flags with a new set as well. The :flags tagged argument is used to associate a set of flags referenced by a variable with the current message. 3.1. Setflag Action Syntax: setflag <variablename: string> <list-of-flags: string-list> Setflag is used for setting [IMAP] system flags or keywords. Setflag replaces any previously set flags. Example: if size :over 500K { setflag "flags" "\\Deleted"; } A more substantial example is: Example: if header :contains "from" "boss@frobnitzm.edu" { setflag "flagvar" "\\Flagged"; fileinto :flags "${flagvar}" "INBOX.From Boss"; } 3.2. Addflag action Syntax: addflag <variablename: string> <list-of-flags: string-list> Addflag is used to add flags to a list of [IMAP] flags. It doesn't replace any previously set flags. This means that multiple occurrences of addflag are treated additively. The order of the flags MAY NOT be preserved and duplicates are allowed. The following examples demonstrate requirements described in 2.1. The following two actions addflag "flagvar" "\\Deleted"; addflag "flagvar" "\\Answered"; produce the same result as the single action addflag "flagvar" ["\\Deleted", "\\Answered"]; or addflag "flagvar" "\\Deleted \\Answered"; or addflag "flagvar" "\\Answered \\Deleted"; 3.3. Removeflag Action Syntax: removeflag <variablename: string> <list-of-flags: string-list> Removeflag is used to remove flags from a list of [IMAP] flags. Removeflag clears flags previously set by "set"/"addflag". Calling removeflag with a flag that wasn't set before is not an error and is ignored. Note, that if an implementation doesn't perform automatic duplicate elimination, it MUST remove all occurences of the flags specified in the second parameter to removeflag. Empty strings in the list-of-flags MUST be ignored. Also note, that flag names are case-insensitive, as described in [IMAP]. Multiple removeflag actions are treated additively. Example: if header :contains "Disposition-Notification-To" "mel@example.com" { addflag "flagvar" "$MDNRequired"; } if header :contains "from" "imap@cac.washington.edu" { removeflag "flagvar" "$MDNRequired"; fileinto :flags "${flagvar}" "INBOX.imap-list"; } 4. Test hasflag Syntax: hasflag [MATCH-TYPE] <variable-list: string-list> <list-of-flags: string-list> The "hasflag" test evaluates to true if any of the variables matches any flag name. The type of match defaults to ":is". Flagname comparisons is always done with the "i;ascii-casemap" operator, i.e., case-insensitive comparisons, as defined in [IMAP]. Note, that if an implementation automatically performs flags reordering and/or duplicate elimination, it MUST perform it on both variable-list values and flag-list values. This is required so that, when the variable "MyFlags" has the value "A B", the following test hasflag :is "MyFlags" "b A" evaluates to true as expected. The above test can be also written as hasflag "MyFlags" ["b","A"] 5. Tagged argument :flags This specification adds a new optional tagged argument ":flags" that alter the behavior of actions "keep" and "fileinto". The :flags tagged argument specifies that the flags provided in the subsequent argument should be set when fileinto/keep deliver the message to the target mailbox/user's main mailbox. If the :flags tagged argument is not specified, "keep" or "fileinto" will not set any flag when they deliver the message to the mailbox. Syntax: ":flags" <list-of-flags: string-list> The copy of the message filed into mailbox will have only flags listed after ":flags". The Sieve interpreter MUST ignore all flags that it can't store permanently. This means that the interpreter must not treat failure to store any flag as a runtime failure to execute the Sieve script. For example, if the mailbox "INBOX.From Boss" can't store any flags, then fileinto :flags "\\Deleted" "INBOX.From Boss"; and fileinto "INBOX.From Boss"; are equivalent. This document doesn't dictate how the Sieve interpreter will set the [IMAP] flags. In particular, the Sieve interpreter may work as an IMAP client, or may have direct access to the mailstore. 6. Implementation Notes "Addflag <variable> <flaglist>" can be implemented as several actions "set <variable> "${variable} <flag>", where <flag> is a flag in flaglist. A script interpreter MAY reorder flags and remove duplicates from the list. A SIEVE script write MUST NOT assume that the order or duplicates will be preserved. << A "hasflag <variable> <flag>" test can be implemented as follows: anyof (string :is :comparator "i;ascii-casemap" "<variable>" "<flag>", /* a flag is in the middle */ string :matches :comparator "i;ascii-casemap" "<variable>" "* <flag> *", /* a flag is the first in the list */ string :matches :comparator "i;ascii-casemap" "<variable>" "<flag> *", /* a flag is the last in the list */ string :matches :comparator "i;ascii-casemap" "<variable>" "* <flag>") "Setflag <variable> [<flag1>,<flag2>,...]" can be implemented as follows: set <variable> "${<flag1>} ${<flag2>} ... ${<flagN>}" "Removeflag <variable> <flag>" can be implemented as (note that this version doesn't remove duplicated flags): if string :is :comparator "i;ascii-casemap" "<variable>" "<flag>" { set <variable> ""; } /* a flag is in the middle */ elsif string :matches :comparator "i;ascii-casemap" "<variable>" "* <flag> *" { set <variable> "${1}${2}"; } /* a flag is the first in the list */ elsif string :matches :comparator "i;ascii-casemap" "<variable>" "<flag> *" { set <variable> "${1}"; } /* a flag is the last in the list */ elsif string :matches :comparator "i;ascii-casemap" "<variable>" "* <flag>" { set <variable> "${1}"; } >> 7. Interaction with Other Sieve Actions This extension work only on the message that is currently being processed by Sieve, it doesn't affect another message generated as a side affect of any action. The extension decribed in this document doesn't change an implicit keep (see section 2.10.2 of [SIEVE]). 8. Other Considerations This extension intentionally doesn't allow setting [IMAP] flags on an arbitrary message in the [IMAP] message store. 9. Security Considerations Security considerations are discussed in the [IMAP] and [SIEVE]. It is belived that this extension doesn't introduce any additional security concerns. 10. Extended example # # Example Sieve Filter # Declare any optional features or extension used by the script # require ["fileinto", "imapflags", "variables"]; # # Move large messages to special mailbox # if size :over 1M { addflag "MyFlags" "Big"; if header :is "From" "boss@company.com" { # The message will be marked as "\Flagged Big" when filed into # mailbox "Big messages" addflag "MyFlags" "\\Flagged"; } fileinto :flags "${MyFlags}" "Big messages"; } if header :is "From" "grandma@example.net" { addflag "MyFlags" ["\\Answered", "$MDNSent"]; # If the message is bigger than 1Mb it will be marked as # "Big \Answered $MDNSent" when filed into mailbox "grandma". # If the message is shorter than 1Mb it will be marked as # "\Answered $MDNSent" fileinto :flags "${MyFlags}" "GrandMa"; # move to "GrandMa" folder } # # Handle messages from known mailing lists # Move messages from IETF filter discussion list to filter folder # if header :is "Sender" "owner-ietf-mta-filters@imc.org" { set "MyFlags" "\\Flagged $Work"; # Message will have both "\Flagged" and $Work flags keep :flags "${MyFlags}"; } # # Keep all messages to or from people in my company # elsif anyof address :domain :is ["From", "To"] "company.com" { keep :flags "${MyFlags}"; # keep in "Inbox" folder } # # Try and catch unsolicited email. If a message is not to me, # or it contains a subject known to be spam, file it away. # elsif anyof (not address :all :contains ["To", "Cc"] "me@company.com", header :matches "subject" ["*make*money*fast*", "*university*dipl*mas*"]) { remove "MyFlags" "\\Flagged"; # If message header does not contain my address, # it's from a list. fileinto :flags "${MyFlags}" "spam"; # move to "spam" folder } else { # Move all other (non-company) mail to "personal" # folder. fileinto :flags "${MyFlags}" "personal"; } 11. Acknowledgments This document has been revised in part based on comments and discussions which took place on and off the Sieve mailing list. The help of those who took the time to review the draft and make suggestions is appreciated, especially that of Tim Showalter, Barry Leiba, Randall Gellens, Ken Murchison, Cyrus Daboo, Matthew Elvey, Jutta Degener, Ned Freed, Marc Mutz, Nigel Swinson and Kjetil Torgrim Homme. Special thanks to Tony Hansen and David Lamb for helping me better explain the concept. 12. Author's Address Alexey Melnikov Isode Limited 5 Castle Business Village Hampton, Middlesex United Kingdom, TW12 2BX Email: alexey.melnikov@isode.com 13. Normative References [SIEVE] Showalter, T., "Sieve: A Mail Filtering Language", Mirapoint, RFC 3028, January 2001. [ABNF] Crocker, D., "Augmented BNF for Syntax Specifications: ABNF", Internet Mail Consortium, RFC 2234, November, 1997. [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", Harvard University, RFC 2119, March 1997. [IMAP] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", University of Washington, RFC 3501, March 2003. [Variables] Homme, K. T., "Sieve -- Variables Extension", University of Oslo, work in progress, draft-homme-sieve-variables-XX.txt 14. Full Copyright Statement Copyright (C) The Internet Society 2000-2004. All Rights Reserved. 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