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Network Working Group                                           N. FreedRequest for Comments: 5260                              Sun MicrosystemsCategory: Standards Track                                      July 2008Sieve Email Filtering: Date and Index ExtensionsStatus 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 "date" and "index" extensions to the   Sieve email filtering language.  The "date" extension gives Sieve the   ability to test date and time values in various ways.  The "index"   extension provides a means to limit header and address tests to   specific instances of header fields when header fields are repeated.Table of Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .22.  Conventions Used in This Document  . . . . . . . . . . . . . .23.  Capability Identifiers . . . . . . . . . . . . . . . . . . . .34.  Date Test  . . . . . . . . . . . . . . . . . . . . . . . . . .34.1.  Zone and Originalzone Arguments  . . . . . . . . . . . . .44.2.  Date-part Argument . . . . . . . . . . . . . . . . . . . .44.3.  Comparator Interactions with Date-part Arguments . . . . .54.4.  Examples . . . . . . . . . . . . . . . . . . . . . . . . .65.  Currentdate Test . . . . . . . . . . . . . . . . . . . . . . .65.1.  Examples . . . . . . . . . . . . . . . . . . . . . . . . .66.  Index Extension  . . . . . . . . . . . . . . . . . . . . . . .76.1.  Example  . . . . . . . . . . . . . . . . . . . . . . . . .87.  Security Considerations  . . . . . . . . . . . . . . . . . . .88.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .99.  References . . . . . . . . . . . . . . . . . . . . . . . . . .99.1.  Normative References . . . . . . . . . . . . . . . . . . .99.2.  Informative References . . . . . . . . . . . . . . . . . .10Appendix A.  Julian Date Conversions . . . . . . . . . . . . . . .11Appendix B.  Acknowledgements  . . . . . . . . . . . . . . . . . .12Freed                       Standards Track                     [Page 1]

RFC 5260            Sieve Date and Index Extensions            July 20081.  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 meant to   be extensible, simple, and independent of access protocol, mail   architecture, and operating system.  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 does not have user-controlled loops or the   ability to run external programs.   The "date" extension provides a new date test to extract and match   date/time information from structured header fields.  The date test   is similar in concept to the address test specified in [RFC5228],   which performs similar operations on addresses in header fields.   The "date" extension also provides a currentdate test that operates   on the date and time when the Sieve script is executed.   Some header fields containing date/time information, e.g., Received:,   naturally occur more than once in a single header.  In such cases it   is useful to be able to restrict the date test to some subset of the   fields that are present.  For example, it may be useful to apply a   date test to the last (earliest) Received: field.  Additionally, it   may also be useful to apply similar restrictions to either the header   or address tests specified in [RFC5228].   For this reason, this specification also defines an "index"   extension.  This extension adds two additional tagged arguments   :index and :last to the header, address, and date tests.  If present,   these arguments specify which occurrence of the named header field is   to be tested.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 inRFC 2119 [RFC2119].   The terms used to describe the various components of the Sieve   language are taken fromSection 1.1 of [RFC5228].Section 2 of the   same document describes basic Sieve language syntax and semantics.   The date-time syntactic element defined using ABNF notation [RFC5234]   in [RFC3339] is also used here.Freed                       Standards Track                     [Page 2]

RFC 5260            Sieve Date and Index Extensions            July 20083.  Capability Identifiers   The capability strings associated with the two extensions defined in   this document are "date" and "index".4.  Date Test   Usage:   date [<":zone" <time-zone: string>> / ":originalzone"]                 [COMPARATOR] [MATCH-TYPE] <header-name: string>                 <date-part: string> <key-list: string-list>   The date test matches date/time information derived from headers   containing [RFC2822] date-time values.  The date/time information is   extracted from the header, shifted to the specified time zone, and   the value of the given date-part is determined.  The test returns   true if the resulting string matches any of the strings specified in   the key-list, as controlled by the comparator and match keywords.   The date test returns false unconditionally if the specified header   field does not exist, the field exists but does not contain a   syntactically valid date-time specification, the date-time isn't   valid according to the rules of the calendar system (e.g., January   32nd, February 29 in a non-leap year), or the resulting string fails   to match any key-list value.   The type of match defaults to ":is" and the default comparator is   "i;ascii-casemap".   Unlike the header and address tests, the date test can only be   applied to a single header field at a time.  If multiple header   fields with the same name are present, only the first field that is   found is used.  (Note, however, that this behavior can be modified   with the "index" extension defined below.)  These restrictions   simplify the test and keep the meaning clear.   The "relational" extension [RFC5231] adds a match type called   ":count".  The count of a date test is 1 if the specified field   exists and contains a valid date; 0, otherwise.   Implementations MUST support extraction ofRFC 2822 date-time   information that either makes up the entire header field (e.g., as it   does in a standard Date: header field) or appears at the end of a   header field following a semicolon (e.g., as it does in a standard   Received: header field).  Implementations MAY support extraction of   date and time information inRFC2822 or other formats that appears in   other positions in header field content.  In the case of a field   containing more than one date or time value, the last one that   appears SHOULD be used.Freed                       Standards Track                     [Page 3]

RFC 5260            Sieve Date and Index Extensions            July 20084.1.  Zone and Originalzone Arguments   The :originalzone argument specifies that the time zone offset   originally in the extracted date-time value should be retained.  The   :zone argument specifies a specific time zone offset that the date-   time value is to be shifted to prior to testing.  It is an error to   specify both :zone and :originalzone.   The value of time-zone MUST be an offset relative to UTC with the   following syntax:       time-zone  =  ( "+" / "-" ) 4DIGIT   The "+" or "-" indicates whether the time-of-day is ahead of (i.e.,   east of) or behind (i.e., west of) UTC.  The first two digits   indicate the number of hours difference from Universal Time, and the   last two digits indicate the number of minutes difference from   Universal Time.  Note that this agrees with theRFC 2822 format for   time zone offsets, not the ISO 8601 format.   If both the :zone and :originalzone arguments are omitted, the local   time zone MUST be used.4.2.  Date-part Argument   The date-part argument specifies a particular part of the resulting   date/time value to match against the key-list.  Possible case-   insensitive values are:     "year"      => the year, "0000" .. "9999".     "month"     => the month, "01" .. "12".     "day"       => the day, "01" .. "31".     "date"      => the date in "yyyy-mm-dd" format.     "julian"    => the Modified Julian Day, that is, the date                    expressed as an integer number of days since                    00:00 UTC on November 17, 1858 (using the Gregorian                    calendar).  This corresponds to the regular                    Julian Day minus 2400000.5.  Sample routines to                    convert to and from modified Julian dates are                    given inAppendix A.     "hour"      => the hour, "00" .. "23".     "minute"    => the minute, "00" .. "59".     "second"    => the second, "00" .. "60".     "time"      => the time in "hh:mm:ss" format.     "iso8601"   => the date and time in restricted ISO 8601 format.     "std11"     => the date and time in a format appropriate                    for use in a Date: header field [RFC2822].Freed                       Standards Track                     [Page 4]

RFC 5260            Sieve Date and Index Extensions            July 2008     "zone"      => the time zone in use.  If the user specified a                    time zone with ":zone", "zone" will                    contain that value.  If :originalzone is specified                    this value will be the original zone specified                    in the date-time value.  If neither argument is                    specified the value will be the server's default                    time zone in offset format "+hhmm" or "-hhmm".  An                    offset of 0 (Zulu) always has a positive sign.     "weekday"   => the day of the week expressed as an integer between                    "0" and "6". "0" is Sunday, "1" is Monday, etc.   The restricted ISO 8601 format is specified by the date-time ABNF   production given in[RFC3339], Section 5.6, with the added   restrictions that the letters "T" and "Z" MUST be in upper case, and   a time zone offset of zero MUST be represented by "Z" and not   "+00:00".4.3.  Comparator Interactions with Date-part Arguments   Not all comparators are suitable with all date-part arguments.  In   general, the date-parts can be compared and tested for equality with   either "i;ascii-casemap" (the default) or "i;octet", but there are   two exceptions:   julian  This is an integer, and may or may not have leading zeros.           As such, "i;ascii-numeric" is almost certainly the best           comparator to use with it.   std11   This is provided as a means to obtain date/time values in a           format appropriate for inclusion in email header fields.  The           wide range of possible syntaxes for a std11 date/time --           which implementations of this extension are free to use when           composing a std11 string -- makes this format a poor choice           for comparisons.  Nevertheless, if a comparison must be           performed, this is case-insensitive, and therefore "i;ascii-           casemap" needs to be used.   "year", "month", "day", "hour", "minute", "second" and "weekday" all   use fixed-width string representations of integers, and can therefore   be compared with "i;octet", "i;ascii-casemap", and "i;ascii-numeric"   with equivalent results.   "date" and "time" also use fixed-width string representations of   integers, and can therefore be compared with "i;octet" and "i;ascii-   casemap"; however, "i;ascii-numeric" can't be used with it, as   "i;ascii-numeric" doesn't allow for non-digit characters.Freed                       Standards Track                     [Page 5]

RFC 5260            Sieve Date and Index Extensions            July 20084.4.  Examples   The Date: field can be checked to test when the sender claims to have   created the message and act accordingly:     require ["date", "relational", "fileinto"];     if allof(header :is "from" "boss@example.com",              date :value "ge" :originalzone "date" "hour" "09",              date :value "lt" :originalzone "date" "hour" "17")     { fileinto "urgent"; }   Testing the initial Received: field can provide an indication of when   a message was actually received by the local system:     require ["date", "relational", "fileinto"];     if anyof(date :is "received" "weekday" "0",              date :is "received" "weekday" "6")     { fileinto "weekend"; }5.  Currentdate Test   Usage:   currentdate [":zone" <time-zone: string>]                        [COMPARATOR] [MATCH-TYPE]                        <date-part: string>                        <key-list: string-list>   The currentdate test is similar to the date test, except that it   operates on the current date/time rather than a value extracted from   the message header.  In particular, the ":zone" and date-part   arguments are the same as those in the date test.   All currentdate tests in a single Sieve script MUST refer to the same   point in time during execution of the script.   The :count value of a currentdate test is always 1.5.1.  Examples   The simplest use of currentdate is to have an action that only   operates at certain times.  For example, a user might want to have   messages redirected to their pager after business hours and on   weekends:Freed                       Standards Track                     [Page 6]

RFC 5260            Sieve Date and Index Extensions            July 2008     require ["date", "relational"];     if anyof(currentdate :is "weekday" "0",              currentdate :is "weekday" "6",              currentdate :value "lt" "hour" "09",              currentdate :value "ge" "hour" "17")     { redirect "pager@example.com"; }   Currentdate can be used to set up vacation [RFC5230] responses in   advance and to stop response generation automatically:     require ["date", "relational", "vacation"];     if allof(currentdate :value "ge" "date" "2007-06-30",              currentdate :value "le" "date" "2007-07-07")     { vacation :days 7  "I'm away during the first week in July."; }   Currentdate may also be used in conjunction with the variables   extension to pass time-dependent arguments to other tests and   actions.  The following Sieve places messages in a folder named   according to the current month and year:     require ["date", "variables", "fileinto"];     if currentdate :matches "month" "*" { set "month" "${1}"; }     if currentdate :matches "year"  "*" { set "year"  "${1}"; }     fileinto "${month}-${year}";   Finally, currentdate can be used in conjunction with the editheader   extension to insert a header-field containing date/time information:      require ["variables", "date", "editheader"];      if currentdate :matches "std11" "*"        {addheader "Processing-date" "${0}";}6.  Index Extension   The "index" extension, if specified, adds optional :index and :last   arguments to the header, address, and date tests as follows:   Syntax:   date [":index" <fieldno: number> [":last"]]                  [<":zone" <time-zone: string>> / ":originalzone"]                  [COMPARATOR] [MATCH-TYPE] <header-name: string>                  <date-part: string> <key-list: string-list>   Syntax:   header [":index" <fieldno: number> [":last"]]                    [COMPARATOR] [MATCH-TYPE]                    <header-names: string-list> <key-list: string-list>Freed                       Standards Track                     [Page 7]

RFC 5260            Sieve Date and Index Extensions            July 2008   Syntax:   address [":index" <fieldno: number> [":last"]]                     [ADDRESS-PART] [COMPARATOR] [MATCH-TYPE]                     <header-list: string-list> <key-list: string-list>   If :index <fieldno> is specified, the attempts to match a value are   limited to the header field fieldno (beginning at 1, the first named   header field).  If :last is also specified, the count is backwards; 1   denotes the last named header field, 2 the second to last, and so on.   Specifying :last without :index is an error.   :index only counts separate header fields, not multiple occurrences   within a single field.  In particular, :index cannot be used to test   a specific address in an address list contained within a single   header field.   Both header and address allow the specification of more than one   header field name.  If more than one header field name is specified,   all the named header fields are counted in the order specified by the   header-list.6.1.  Example   Mail delivery may involve multiple hops, resulting in the Received:   field containing information about when a message first entered the   local administrative domain being the second or subsequent field in   the message.  As long as the field offset is consistent, it can be   tested:     # Implement the Internet-Draft cutoff date check assuming the     # second Received: field specifies when the message first     # entered the local email infrastructure.     require ["date", "relational", "index"];     if date :value "gt" :index 2 :zone "-0500" "received"             "iso8601" "2007-02-26T09:00:00-05:00",     { redirect "aftercutoff@example.org"; }7.  Security Considerations   The facilities defined here, like the facilities in the base Sieve   specification, operate on message header information that can easily   be forged.  Note, however, that some fields are inherently more   reliable than others.  For example, the Date: field is typically   inserted by the message sender and can be altered at any point.  By   contrast, the uppermost Received: field is typically inserted by the   local mail system and is therefore difficult for the sender or an   intermediary to falsify.Freed                       Standards Track                     [Page 8]

RFC 5260            Sieve Date and Index Extensions            July 2008   Use of the currentdate test makes script behavior inherently less   predictable and harder to analyze.  This may have consequences for   systems that use script analysis to try and spot problematic scripts.   All of the security considerations given in the base Sieve   specification also apply to these extensions.8.  IANA Considerations   The following templates specify the IANA registrations of the two   Sieve extensions specified in this document:      To: iana@iana.org      Subject: Registration of new Sieve extensions      Capability name: date      Description:     The "date" extension gives Sieve the ability                       to test date and time values.      RFC number:RFC 5260      Contact address: Sieve discussion list <ietf-mta-filters@imc.org>      Capability name: index      Description:     The "index" extension provides a means to                       limit header and address tests to specific                       instances when more than one field of a                       given type is present.      RFC number:RFC 5260      Contact address: Sieve discussion list <ietf-mta-filters@imc.org>9.  References9.1.  Normative References   [CALGO199]  Tantzen, R., "Algorithm 199: Conversions Between Calendar               Date and Julian Day Number", Collected Algorithms from               CACM 199.   [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.   [RFC3339]   Klyne, G., Ed. and C. Newman, "Date and Time on the               Internet: Timestamps",RFC 3339, July 2002.   [RFC5228]   Guenther, P. and T. Showalter, "Sieve: An Email Filtering               Language",RFC 5228, January 2008.Freed                       Standards Track                     [Page 9]

RFC 5260            Sieve Date and Index Extensions            July 2008   [RFC5231]   Segmuller, W. and B. Leiba, "Sieve Email Filtering:               Relational Extension",RFC 5231, January 2008.   [RFC5234]   Crocker, D. and P. Overell, "Augmented BNF for Syntax               Specifications: ABNF", STD 68,RFC 5234, January 2008.9.2.  Informative References   [RFC3501]   Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION               4rev1",RFC 3501, March 2003.   [RFC5230]   Showalter, T. and N. Freed, "Sieve Email Filtering:               Vacation Extension",RFC 5230, January 2008.Freed                       Standards Track                    [Page 10]

RFC 5260            Sieve Date and Index Extensions            July 2008Appendix A.  Julian Date Conversions   The following C routines show how to translate day/month/year   information to and from modified Julian dates.  These routines are   straightforward translations of the Algol routines specified in CACM   Algorithm 199 [CALGO199].   Given the day, month, and year, jday returns the modified Julian   date.   int jday(int year, int month, int day)   {       int j, c, ya;       if (month > 2)           month -= 3;       else       {           month += 9;           year--;       }       c = year / 100;       ya = year - c * 100;       return (c * 146097 / 4 + ya * 1461 / 4 + (month * 153 + 2) / 5 +               day + 1721119);   }Freed                       Standards Track                    [Page 11]

RFC 5260            Sieve Date and Index Extensions            July 2008   Given j, the modified Julian date, jdate returns the day, month, and   year.   void jdate(int j, int *year, int *month, int *day)   {       int y, m, d;       j -= 1721119;       y = (j * 4 - 1) / 146097;       j = j * 4 - y * 146097 - 1;       d = j / 4;       j = (d * 4 + 3) / 1461;       d = d * 4 - j * 1461 + 3;       d = (d + 4) / 4;       m = (d * 5 - 3) / 153;       d = d * 5 - m * 153 - 3;       *day = (d + 5) / 5;       *year = y * 100 + j;       if (m < 10)           *month = m + 3;       else       {           *month = m - 9;           *year += 1;       }   }Appendix B.  Acknowledgements   Dave Cridland contributed the text describing the proper comparators   to use with different date-parts.  Cyrus Daboo, Frank Ellerman,   Alexey Melnikov, Chris Newman, Dilyan Palauzov, and Aaron Stone   provided helpful suggestions and corrections.Author's Address   Ned Freed   Sun Microsystems   800 Royal Oaks   Monrovia, CA  91016-6347   USA   Phone: +1 909 457 4293   EMail: ned.freed@mrochek.comFreed                       Standards Track                    [Page 12]

RFC 5260            Sieve Date and Index Extensions            July 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 13]