Movatterモバイル変換

Network Working Group                                       A.  MelnikovRequest for Comments: 5232                                 Isode LimitedCategory: Standards Track                                   January 2008Sieve Email Filtering: Imap4flags 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   Recent discussions have shown that it is desirable to set different   IMAP (RFC 3501) 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 setting of   both IMAP system flags and IMAP keywords.Table of Contents1. Introduction ....................................................21.1. Conventions Used ...........................................22. General Requirements for Flag Handling ..........................33. Actions .........................................................33.1. Action setflag .............................................43.2. Action addflag .............................................43.3. Action removeflag ..........................................54. Test hasflag ....................................................65. Tagged Argument :flags ..........................................76. Interaction with Other Sieve Actions ............................87. Security Considerations .........................................88. IANA Considerations .............................................89. Extended Example ................................................810. Acknowledgments ...............................................1011. Normative References ..........................................10Melnikov                    Standards Track                     [Page 1]

RFC 5232              Sieve: Imap4flags Extension           January 20081.  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   whether a flag belongs to a list.   From the user's perspective, this extension provides several   capabilities.  First, it allows manipulation of sets of IMAP flags.   Second, it gives the ability to associate a set of IMAP flags with a   message that is delivered to a mailstore using the keep/fileinto   actions.  Third, it maintains an internal variable.  The internal   variable contains the default flags that will be associated with a   message that is delivered using the keep, implicit keep, or fileinto   actions, when the :flags tagged argument is not specified.  When the   Sieve [VARIABLES] extension is also supported by the Sieve engine, it   enables support for multiple variables containing sets of IMAP flags.   The capability string associated with the extension defined in this   document is "imap4flags".  All conformant implementations MUST   implement all Sieve actions (setflag, addflag, removeflag), the   "hasflag" test, and the ":flags" tagged argument described in this   document.   The "imap4flags" extension can be used with or without the   "variables" extension [VARIABLES].  When the "variables" extension is   enabled in a script using <require "variables">, the script can use   explicit variable names in setflag/addflag/removeflag actions and the   hasflag test.  See alsoSection 3 for more details.  When the   "variables" extension is not enabled, the explicit variable name   parameter to setflag/addflag/removeflag/hasflag MUST NOT be used and   MUST cause an error according to [SIEVE].1.1.  Conventions Used   Conventions for notations are as in [SIEVE], Section 1.1, including   use of "Usage:" label for the definition of action and tagged   arguments syntax.   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 inRFC 2119.Melnikov                    Standards Track                     [Page 2]

RFC 5232              Sieve: Imap4flags Extension           January 20082.  General Requirements for Flag Handling   The following notes apply to processing of addflag/removeflag/setflag   actions, the "hasflag" test and the ":flags" tagged argument.   A Sieve interpreter MUST ignore empty strings (i.e., "") in a list-   of-flags parameter.   A string containing a space-separated list of flag names is   equivalent to a string list consisting of the flags.  This   requirement is to simplify amalgamation of multiple flag lists.   The Sieve interpreter SHOULD check the list of flags for validity as   described by [IMAP] ABNF.  In particular, according to [IMAP], non-   ASCII characters are not allowed in flag names.  However, spaces MUST   always be allowed as delimiters in strings representing a list of   flags.  In such strings, multiple spaces between flag names MUST be   treated as a single space character, and leading and trailing spaces   MUST be ignored.   If a flag validity check fails, the flag MUST be ignored.   Note that it is not possible to use this extension to set or clear   the \Recent flag or any other special system flag that is not   settable in [IMAP].  Any such flags MUST be ignored if included in a   flag list.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 a space-separated list of flag names.   Any setflag/addflag/removeflag action MAY alter the flag list in any   way that leaves its semantics as a set of case-insensitive words   unaltered.  For example, it may reorder the flags, alter the case of   the letters in them, or add or remove duplicates or extraneous   spaces.  Scripts MUST NOT make assumptions about the ordering of   flags in lists or the preservation of their case.   Note that the parameter specifying a variable name to   setflag/addflag/removeflag actions and the hasflag test is optional.   If the parameter is not specified, the actions operate on the   internal variable, which has the empty value when the script starts   execution.  If the SIEVE interpreter doesn't support the "variables"   extension [VARIABLES], the presence of the variable name parameter   will cause a runtime error [SIEVE].Melnikov                    Standards Track                     [Page 3]

RFC 5232              Sieve: Imap4flags Extension           January 2008   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 replace an existing set of   flags with a new set as well.  However, it should be noted that the   "set" action can't perform any flag reordering, duplicate   elimination, etc.   The :flags tagged argument to "keep" and "fileinto" actions is used   to associate a set of flags with the current message.  If the :flags   tagged argument is not specified with those two actions, the current   value of the internal variable is used instead.  The value of the   internal variable also applies to the implicit keep.   Note that when keep/fileinto is used multiple times in a script and   duplicate message elimination is performed (as described inSection2.10.3 of [SIEVE]), the last flag list value MUST win.3.1.  Action setflag   Usage:   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 "\\Deleted";             }   A more substantial example is the following:   Example:        if header :contains "from" "boss@frobnitzm.example.edu" {            setflag "flagvar" "\\Flagged";            fileinto :flags "${flagvar}" "INBOX.From Boss";        }3.2.  Action addflag   Usage:   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.Melnikov                    Standards Track                     [Page 4]

RFC 5232              Sieve: Imap4flags Extension           January 2008   The following examples demonstrate requirements described inSection2.1.  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.  Action removeflag   Usage:   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 occurrences 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" "$MDNRequired";        }        if header :contains "from" "imap@cac.washington.example.edu" {            removeflag "flagvar" "$MDNRequired";            fileinto :flags "${flagvar}" "INBOX.imap-list";        }Melnikov                    Standards Track                     [Page 5]

RFC 5232              Sieve: Imap4flags Extension           January 20084.  Test hasflag   Usage: hasflag [MATCH-TYPE] [COMPARATOR]          [<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".  If the list of   variables is omitted, value of the internal variable is used instead.   The default comparator is "i;ascii-casemap", which is the same case-   insensitive comparison as defined for IMAP flags by [IMAP].   The "relational" extension [RELATIONAL] adds a match type called   ":count".  The :count of a variable returns the number of distinct   flags in it.  The count of a list of variables is the sum of the   counts of the member variables.   Example:     If the internal variable has the value "A B", the following test      hasflag :is "b A"     evaluates to true.  The above test can also be written as      hasflag ["b","A"]   Example:     If the variable "MyVar" has value "NonJunk Junk gnus-forward     $Forwarded NotJunk JunkRecorded $Junk $NotJunk", the following     tests evaluate to true:      hasflag :contains "MyVar" "Junk"      hasflag :contains "MyVar" "forward"      hasflag :contains "MyVar" ["label", "forward"]      hasflag :contains "MyVar" ["junk", "forward"]     Note that the last of these tests can be rewritten     as      hasflag :contains "MyVar" "junk forward"     or      hasflag :contains "MyVar" "forward junk"     However, the last two forms are not recommended.Melnikov                    Standards Track                     [Page 6]

RFC 5232              Sieve: Imap4flags Extension           January 2008     And the following tests will evaluate to false:      hasflag :contains "MyVar" "label"      hasflag :contains "MyVar" ["label1", "label2"]   Example:     If the variable "MyFlags" has the value "A B", the following test       hasflag :count "ge" :comparator "i;ascii-numeric"               "MyFlags" "2"     evaluates to true, as the variable contains 2 distinct flags.5.  Tagged Argument :flags   This specification adds a new optional tagged argument ":flags" that   alters 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 delivers the   message to the target mailbox/user's main mailbox.  If the :flags   tagged argument is not specified, "keep" or "fileinto" will use the   current value of the internal variable when delivering the message to   the target mailbox.   Usage:   ":flags" <list-of-flags: string-list>   The copy of the message filed into the mailbox will have only flags   listed after the :flags tagged argument.   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.Melnikov                    Standards Track                     [Page 7]

RFC 5232              Sieve: Imap4flags Extension           January 20086.  Interaction with Other Sieve Actions   This extension works only on the message that is currently being   processed by Sieve; it doesn't affect another message generated as a   side effect of any action or any other message already in the   mailstore.   The extension described in this document doesn't change the implicit   keep (see Section 2.10.2 of [SIEVE]).7.  Security Considerations   Security considerations are discussed in [IMAP], [SIEVE], and   [VARIABLES].   This extension intentionally doesn't allow setting [IMAP] flags on an   arbitrary message in the [IMAP] message store.   It is believed that this extension doesn't introduce any additional   security concerns.8.  IANA Considerations   The following template specifies the IANA registration of the   variables Sieve extension specified in this document:   To: iana@iana.org   Subject: Registration of new Sieve extension   Capability name: imap4flags   Description:     Adds actions and tests for manipulating IMAP flags   RFC number:RFC 5232   Contact address: The Sieve discussion list <ietf-mta-filters@imc.org>   This information has been added to the list of Sieve extensions given   onhttp://www.iana.org/assignments/sieve-extensions.9.  Extended Example   #   # Example Sieve Filter   # Declare any optional features or extension used by the script   #   require ["fileinto", "imap4flags", "variables"];   #   # Move large messages to a special mailbox   #Melnikov                    Standards Track                     [Page 8]

RFC 5232              Sieve: Imap4flags Extension           January 2008   if size :over 1M           {           addflag "MyFlags" "Big";           if header :is "From" "boss@company.example.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";           }   #   # Handle messages from known mailing lists   # Move messages from IETF filter discussion list to filter folder   #   if header :is "Sender" "owner-ietf-mta-filters@example.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.example.com"           {           keep :flags "${MyFlags}"; # keep in "Inbox" folder           }   # Try to 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.example.com",                header :matches "subject"                  ["*make*money*fast*", "*university*dipl*mas*"])Melnikov                    Standards Track                     [Page 9]

RFC 5232              Sieve: Imap4flags Extension           January 2008           {           remove "MyFlags" "\\Flagged";           fileinto :flags "${MyFlags}" "spam";           }   else           {           # Move all other external mail to "personal"           # folder.           fileinto :flags "${MyFlags}" "personal";           }10.  Acknowledgments   This document has been revised in part based on comments and   discussions that took place on and off the Sieve mailing list.   The help of those who took the time to review the document 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, Kjetil Torgrim   Homme, Mark E.  Mallett, Dave Cridland, Arnt Gulbrandsen, Philip   Guenther, Rob Austein, Sam Hartman, Eric Gray, and Cullen Jennings.   Special thanks to Tony Hansen and David Lamb for helping me better   explain the concept.11.  Normative References   [SIEVE]      Guenther, P., Ed., and T. Showalter, Ed., "Sieve: An                Email Filtering Language",RFC 5228, January 2008.   [IMAP]       Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION                4rev1",RFC 3501, March 2003.   [VARIABLES]  Homme, K., "Sieve Email Filtering: Variables Extension",RFC 5229, January 2008.   [RELATIONAL] Segmuller, W. and B. Leiba "Sieve Email Filtering:                Relational Extension",RFC 5231, January 2008.Melnikov                    Standards Track                    [Page 10]

RFC 5232              Sieve: Imap4flags Extension           January 2008Author's Address   Alexey Melnikov   Isode Limited   5 Castle Business Village   Hampton, Middlesex   United Kingdom, TW12 2BX   EMail: alexey.melnikov@isode.comMelnikov                    Standards Track                    [Page 11]

RFC 5232              Sieve: Imap4flags Extension           January 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.Melnikov                    Standards Track                    [Page 12]