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Network Working Group                                       T. ShowalterRequest for Comments: 5230Category: Standards Track                                  N. Freed, Ed.                                                        Sun Microsystems                                                            January 2008Sieve Email Filtering: Vacation 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 an extension to the Sieve email filtering   language for an autoresponder similar to that of the Unix "vacation"   command for replying to messages.  Various safety features are   included to prevent problems such as message loops.Showalter & Freed           Standards Track                     [Page 1]

RFC 5230               Sieve: Vacation Extension            January 2008Table of Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .32.  Conventions Used in This Document  . . . . . . . . . . . . . .33.  Capability Identifier  . . . . . . . . . . . . . . . . . . . .34.  Vacation Action  . . . . . . . . . . . . . . . . . . . . . . .34.1.  Days Parameter . . . . . . . . . . . . . . . . . . . . . .34.2.  Previous Response Tracking . . . . . . . . . . . . . . . .44.3.  Subject and From Parameters  . . . . . . . . . . . . . . .64.4.  MIME Parameter . . . . . . . . . . . . . . . . . . . . . .6     4.5.  Address Parameter and Limiting Replies to Personal           Messages . . . . . . . . . . . . . . . . . . . . . . . . .7     4.6.  Restricting Replies to Automated Processes and Mailing           Lists  . . . . . . . . . . . . . . . . . . . . . . . . . .84.7.  Interaction with Other Sieve Actions . . . . . . . . . . .84.8.  Examples . . . . . . . . . . . . . . . . . . . . . . . . .95.  Response Message Generation  . . . . . . . . . . . . . . . . .95.1.  SMTP MAIL FROM Address . . . . . . . . . . . . . . . . . .95.2.  Date . . . . . . . . . . . . . . . . . . . . . . . . . . .95.3.  Subject  . . . . . . . . . . . . . . . . . . . . . . . . .105.4.  From . . . . . . . . . . . . . . . . . . . . . . . . . . .105.5.  To . . . . . . . . . . . . . . . . . . . . . . . . . . . .105.6.  Auto-Submitted . . . . . . . . . . . . . . . . . . . . . .105.7.  Message Body . . . . . . . . . . . . . . . . . . . . . . .105.8.  In-Reply-To and References . . . . . . . . . . . . . . . .10   6.  Relationship to Recommendations for Automatic Responses to       Electronic Mail  . . . . . . . . . . . . . . . . . . . . . . .117.  Internationalization Considerations  . . . . . . . . . . . . .118.  Security Considerations  . . . . . . . . . . . . . . . . . . .129.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .1210. References . . . . . . . . . . . . . . . . . . . . . . . . . .1310.1. Normative References . . . . . . . . . . . . . . . . . . .1310.2. Informative References . . . . . . . . . . . . . . . . . .13Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . .15Showalter & Freed           Standards Track                     [Page 2]

RFC 5230               Sieve: Vacation Extension            January 20081.  Introduction   This document defines an extension to the Sieve language defined in   [RFC5228] for notification that messages to a particular recipient   will not be answered immediately.2.  Conventions Used in This Document   Conventions for notations are as in[RFC5228] section 1.1.   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", "REQUIRED",   and "MAY" in this document are to be interpreted as defined in   [RFC2119].3.  Capability Identifier   Sieve implementations that implement vacation have an identifier of   "vacation" for use with the capability mechanism.4.  Vacation Action   Usage:   vacation [":days" number] [":subject" string]                     [":from" string] [":addresses" string-list]                     [":mime"] [":handle" string] <reason: string>   The "vacation" action implements a vacation autoresponder similar to   the vacation command available under many versions of Unix.  Its   purpose is to provide correspondents with notification that the user   is away for an extended period of time and that they should not   expect quick responses.   "Vacation" is used to respond to a message with another message.   Vacation's messages are always addressed to the Return-Path address   (that is, the envelope from address) of the message being responded   to.4.1.  Days Parameter   The ":days" argument is used to specify the period in which addresses   are kept and are not responded to, and is always specified in days.   The minimum value used for this parameter is normally 1.  Sites MAY   define a different minimum value as long as the minimum is greater   than 0.  Sites MAY also define a maximum days value, which MUST be   greater than 7, and SHOULD be greater than 30.   If ":days" is omitted, the default value is either 7 or the minimum   value (as defined above), whichever is greater.Showalter & Freed           Standards Track                     [Page 3]

RFC 5230               Sieve: Vacation Extension            January 2008   If the parameter given to ":days" is less than the minimum value,   then the minimum value is used instead.   If ":days" exceeds the site-defined maximum, the site-defined maximum   is used instead.4.2.  Previous Response Tracking   "Vacation" keeps track of all the responses it has sent to each   address in some period (as specified by the :days optional argument).   If vacation has not previously sent the response to this address   within the given time period, it sends the "reason" argument to the   SMTP MAIL FROM address [RFC2821] of the message that is being   responded to.  (The SMTP MAIL FROM address should be available in the   Return-path: header field if Sieve processing occurs after final   delivery.)   Tracking is not just per address, but must also take the vacation   response itself into account.  A script writer might, for example,   have a vacation action that will send a general notice only once in   any two-week period.  However, even if a sender has received this   general notice, it may be important to send a specific notice when a   message about something timely or something specific has been   detected.   A particular vacation response can be identified in one of two ways.   The first way is via an explicit :handle argument, which attaches a   name to the response.  All vacation statements that use the same   handle will be considered the same response for tracking purposes.   The second way is via a synthesis of the :subject, :from, :mime, and   reason vacation command arguments.  All vacation actions that do not   contain an explicit handle and that use an identical combination of   these arguments are considered the same for tracking purposes.   For instance, if coyote@desert.example.org sends mail to   roadrunner@acme.example.com twice, once with the subject "Cyrus bug"   and once with the subject "come over for dinner", and   roadrunner@acme.example.com has the script shown below,   coyote@desert.example.org would receive two responses, one with the   first message, one with the second.   require "vacation";   if header :contains "subject" "cyrus" {       vacation "I'm out -- send mail to cyrus-bugs";   } else {       vacation "I'm out -- call me at +1 304 555 0123";   }Showalter & Freed           Standards Track                     [Page 4]

RFC 5230               Sieve: Vacation Extension            January 2008   In the above example, coyote@desert.example.org gets the second   message despite having gotten the first one because separate vacation   responses have been triggered.  This behavior is REQUIRED.   There is one important exception to this rule, however.  If the Sieve   variables extension [RFC5229] is used, the arguments MUST NOT have   undergone variable expansion prior to their use in response tracking.   This is so that examples like the following script will only generate   a single response to each incoming message with a different subject   line.   require ["vacation", "variables"];   if header :matches "subject" "*" {       vacation :subject "Automatic response to: ${1}"                "I'm away -- send mail to foo in my absence";   }   As noted above, the optional ":handle" parameter can be used to tell   the Sieve interpreter to treat two vacation actions with different   arguments as the same command for purposes of response tracking.  The   argument to ":handle" is a string that identifies the type of   response being sent.  For instance, if tweety@cage.example.org sends   mail to spike@doghouse.example.com twice, one with the subject   "lunch?" and once with the subject "dinner?", and   spike@doghouse.example.com has the script shown below,   tweety@cage.example.org will only receive a single response.  (Which   response is sent depends on the order in which the messages are   processed.)   require "vacation";   if header :contains "subject" "lunch" {       vacation :handle "ran-away" "I'm out and can't meet for lunch";   } else {       vacation :handle "ran-away" "I'm out";   }   NOTE: One way to implement the necessary mechanism here is to store a   hash of either the current handle and the recipient address or, if no   handle is provided, a hash of the vacation action parameters   specifying the message content and the recipient address.  If a   script is changed, implementations MAY reset the records of who has   been responded to and when they have been responded to.   IMPLEMENTATION NOTE: Care must be taken in constructing a hash of   vacation action parameters.  In particular, since most parameters are   optional, it is important not to let the same string used as the   value for different parameters produce the same hash value.  OneShowalter & Freed           Standards Track                     [Page 5]

RFC 5230               Sieve: Vacation Extension            January 2008   possible way to accomplish this is to apply the hash to a series of   counted or null terminated strings, one for each possible parameter   in particular order.   Implementations are free to limit the number of remembered responses;   however, the limit MUST NOT be less than 1000.  When limiting the   number of tracked responses, implementations SHOULD discard the   oldest ones first.4.3.  Subject and From Parameters   The ":subject" parameter specifies a subject line to attach to any   vacation response 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 generate an appropriate default   subject line as specified below if no :subject parameter is   specified.   A ":from" parameter may be used to specify an alternate address to   use in the From field of vacation messages.  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 specified in a ":from" parameter; it is   suggested that values that fail such a validity check simply be   ignored rather than cause the vacation action to fail.4.4.  MIME Parameter   The ":mime" parameter, if supplied, specifies that the reason string   is, in fact, a MIME entity as defined in[RFC2045] section 2.4,   including both MIME headers and content.   If the optional :mime parameter is not supplied, the reason string is   considered a UTF-8 string.Showalter & Freed           Standards Track                     [Page 6]

RFC 5230               Sieve: Vacation Extension            January 2008   require "vacation";   vacation :mime text:   Content-Type: multipart/alternative; boundary=foo   --foo   I'm at the beach relaxing.  Mmmm, surf...   --foo   Content-Type: text/html; charset=us-ascii   <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"    "http://www.w3.org/TR/REC-html40/strict.dtd">   <HTML><HEAD><TITLE>How to relax</TITLE>   <BASE HREF="http://home.example.com/pictures/"></HEAD>   <BODY><P>I'm at the <A HREF="beach.gif">beach</A> relaxing.   Mmmm, <A HREF="ocean.gif">surf</A>...   </BODY></HTML>   --foo--   .4.5.  Address Parameter and Limiting Replies to Personal Messages   "Vacation" MUST NOT respond to a message unless the recipient user's   email address is in a "To", "Cc", "Bcc", "Resent-To", "Resent-Cc", or   "Resent-Bcc" line of the original message.  An email address is   considered to belong to the recipient if it is one of:   1.  an email address known by the implementation to be associated       with the recipient,   2.  the final envelope recipient address if it's available to the       implementation, or   3.  an address specified by the script writer via the ":addresses"       argument described in the next paragraph.   Users can supply additional mail addresses that are theirs with the   ":addresses" argument, which takes a string-list listing additional   addresses that a user might have.  These addresses are considered to   belong to the recipient user in addition to the addresses known to   the implementation.Showalter & Freed           Standards Track                     [Page 7]

RFC 5230               Sieve: Vacation Extension            January 20084.6.  Restricting Replies to Automated Processes and Mailing Lists   Implementations MAY refuse to send a vacation response to a message   that contains any header or content that makes it appear that a   response would not be appropriate.   Implementations MUST have a list of addresses that "vacation" MUST   NOT send mail to.  However, the contents of this list are   implementation defined.  The purpose of this list is to stop mail   from going to addresses used by system daemons that would not care if   the user is actually reading her mail.   Implementations are encouraged, however, to include well-known   addresses like "MAILER-DAEMON", "LISTSERV", "majordomo", and other   addresses typically used only by automated systems.  Additionally,   addresses ending in "-request" or beginning in "owner-", i.e.,   reserved for mailing list software, are also suggested.   Implementors may take guidance from [RFC2142], but should be careful.   Some addresses, like "POSTMASTER", are generally actually managed by   people, and people do care if the user is going to be unavailable.   Implementations SHOULD NOT respond to any message that contains a   "List-Id" [RFC2919], "List-Help", "List-Subscribe", "List-   Unsubscribe", "List-Post", "List-Owner", or "List-Archive" [RFC2369]   header field.   Implementations SHOULD NOT respond to any message that has an "Auto-   submitted" header field with a value other than "no".  This header   field is described in [RFC3834].4.7.  Interaction with Other Sieve Actions   Vacation does not affect Sieve's implicit keep action.   Vacation can only be executed once per script.  A script MUST fail   with an appropriate error if it attempts to execute two or more   vacation actions.   Implementations MUST NOT consider vacation used with discard, keep,   fileinto, or redirect an error.  The vacation action is incompatible   with the Sieve reject and refuse actions [REJECT].Showalter & Freed           Standards Track                     [Page 8]

RFC 5230               Sieve: Vacation Extension            January 20084.8.  Examples   Here is a simple use of vacation.   require "vacation";   vacation :days 23 :addresses ["tjs@example.edu",                                 "ts4z@landru.example.edu"]   "I'm away until October 19.   If it's an emergency, call 911, I guess." ;   By mingling vacation with other rules, users can do something more   selective.   require "vacation";   if header :contains "from" "boss@example.edu" {       redirect "pleeb@isp.example.org";   } else {       vacation "Sorry, I'm away, I'll read your   message when I get around to it.";   }5.  Response Message Generation   This section details the requirements for the generated response   message.   It is worth noting that the input message and arguments may be in   UTF-8, and that implementations MUST deal with UTF-8 input, although   implementations MAY transcode to other character sets as regional   taste dictates.  When :mime is used, the reason argument also   contains MIME header information.  The headers must conform to MIME   conventions; in particular, 8bit text is not allowed.   Implementations SHOULD reject vacation :mime actions containing 8bit   header material.5.1.  SMTP MAIL FROM Address   The SMTP MAIL FROM address of the message envelope SHOULD be set to   <>.  NOTIFY=NEVER SHOULD also be set in the RCPT TO line during the   SMTP transaction if the NOTARY SMTP extension [RFC3461] is available.5.2.  Date   The Date field SHOULD be set to the date and time when the vacation   response was generated.  Note that this may not be the same as the   time the message was delivered to the user.Showalter & Freed           Standards Track                     [Page 9]

RFC 5230               Sieve: Vacation Extension            January 20085.3.  Subject   Users can specify the Subject of the reply with the ":subject"   parameter.  If the :subject parameter is not supplied, then the   subject is generated as follows: The subject is set to the characters   "Auto: " followed by the original subject.  An appropriate fixed   Subject, such as "Automated reply", SHOULD be used in the event that   :subject isn't specified and the original message doesn't contain a   Subject field.5.4.  From   Unless explicitly overridden with a :from parameter, the From field   SHOULD be set to the address of the owner of the Sieve script.5.5.  To   The To field SHOULD be set to the address of the recipient of the   response.5.6.  Auto-Submitted   An Auto-Submitted field with a value of "auto-replied" SHOULD be   included in the message header of any vacation message sent.5.7.  Message Body   The body of the message is taken from the reason string in the   vacation command.5.8.  In-Reply-To and References   Replies MUST have the In-Reply-To field set to the Message-ID of the   original message, and the References field SHOULD be updated with the   Message-ID of the original message.   If the original message lacks a Message-ID, an In-Reply-To need not   be generated, and References need not be changed.Section 3.6.4 of [RFC2822] provides a complete description of how   References fields should be generated.Showalter & Freed           Standards Track                    [Page 10]

RFC 5230               Sieve: Vacation Extension            January 20086.  Relationship to Recommendations for Automatic Responses to    Electronic Mail   The vacation extension implements a "Personal Responder" in the   terminology defined in [RFC3834].  Care has been taken in this   specification to comply with the recommendations of [RFC3834]   regarding how personal responders should behave.7.  Internationalization Considerations   Internationalization capabilities provided by the base Sieve language   are discussed in [RFC5228].  However, the vacation extension is the   first Sieve extension to be defined that is capable of creating   entirely new messages.  This section deals with internationalization   issues raised by the use of the vacation extension.   Vacation messages are normally written using the UTF-8 charset,   allowing text to be written in most of the world's languages.   Additionally, the :mime parameter allows specification of arbitrary   MIME content.  In particular, this makes it possible to use   multipart/alternative objects to specify vacation responses in   multiple languages simultaneously.   The Sieve language itself allows a vacation response to be selected   based on the content of the original message.  For example, the   Accept-Language or Content-Language header fields [RFC3282] could be   checked and used to select appropriate text:   require "vacation";   if header :contains ["accept-language", "content-language"] "en"   {       vacation "I am away this week.";   } else {       vacation "Estoy ausente esta semana.";   }   Note that this rather simplistic test of the field values fails to   take the structure of the fields into account and hence could be   fooled by some more complex field values.  A more elaborate test   could be used to deal with this problem.   The approach of explicitly coding language selection criteria in   scripts is preferred because in many cases language selection issues   are conflated with other selection issues.  For example, it may be   appropriate to use informal text in one language for vacation   responses sent to a fellow employee while using more formal text in a   different language in a response sent to a total stranger outside the   company:Showalter & Freed           Standards Track                    [Page 11]

RFC 5230               Sieve: Vacation Extension            January 2008   require "vacation";   if address :matches "from" "*@ourdivision.example.com"   {       vacation :subject "Gone fishing"                "Having lots of fun! Back in a day or two!";   } else {       vacation :subject "Je suis parti cette semaine"                "Je lirai votre message quand je retourne.";   }   IMPLEMENTATION NOTE: A graphical Sieve generation interface could in   principle be used to hide the complexity of specifying response   selection criteria from end users.  Figuring out the right set of   options to present in a graphical interface is likely a nontrivial   proposition, but this is more because of the need to employ a variety   of criteria to select different sorts of responses to send to   different classes of people than because of the issues involved in   selecting a response in an appropriate language.8.  Security Considerations   It is critical that implementations correctly implement the behavior   and restrictions described throughout this document.  Replies MUST   NOT be sent out in response to messages not sent directly to the   user, and replies MUST NOT be sent out more often than the :days   argument states unless the script changes.   If mail is forwarded from a site that uses subaddressing, it may be   impossible to list all recipient addresses with ":addresses".   Security issues associated with mail auto-responders are fully   discussed in the security considerations section of [RFC3834].  This   document is believed not to introduce any additional security   considerations in this general area.9.  IANA Considerations   The following template specifies the IANA registration of the   vacation Sieve extension specified in this document:   To: iana@iana.org   Subject: Registration of new Sieve extension   Capability name: vacation   Description:     adds an action for generating an auto-reply saying                    that the original message will not be read or                    answered immediately   RFC number:RFC 5230Showalter & Freed           Standards Track                    [Page 12]

RFC 5230               Sieve: Vacation Extension            January 2008   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.10.  References10.1.  Normative References   [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.   [RFC3461]  Moore, K., "Simple Mail Transfer Protocol (SMTP) Service              Extension for Delivery Status Notifications (DSNs)",RFC 3461, January 2003.   [RFC3834]  Moore, K., "Recommendations for Automatic Responses to              Electronic Mail",RFC 3834, August 2004.   [RFC5228]  Guenther, P., Ed. and T. Showalter, Ed., "Sieve: An Email              Filtering Language",RFC 5228, January 2008.   [RFC5229]  Homme, K., "Sieve Email Filtering: Variables Extension",RFC 5229, January 2008.10.2.  Informative References   [REJECT]   Stone, A., Elvey, M., and A. Melnikov, "Sieve Email              Filtering: Reject Extension", Work in Progress,              October 2007.   [RFC2142]  Crocker, D., "MAILBOX NAMES FOR COMMON SERVICES, ROLES AND              FUNCTIONS",RFC 2142, May 1997.   [RFC2369]  Neufeld, G. and J. Baer, "The Use of URLs as Meta-Syntax              for Core Mail List Commands and their Transport through              Message Header Fields",RFC 2369, July 1998.Showalter & Freed           Standards Track                    [Page 13]

RFC 5230               Sieve: Vacation Extension            January 2008   [RFC2821]  Klensin, J., "Simple Mail Transfer Protocol",RFC 2821,              April 2001.   [RFC2919]  Chandhok, R. and G. Wenger, "List-Id: A Structured Field              and Namespace for the Identification of Mailing Lists",RFC 2919, March 2001.   [RFC3282]  Alvestrand, H., "Content Language Headers",RFC 3282,              May 2002.Showalter & Freed           Standards Track                    [Page 14]

RFC 5230               Sieve: Vacation Extension            January 2008Appendix A.  Acknowledgements   This extension is obviously inspired by Eric Allman's vacation   program under Unix.  The authors owe a great deal to Carnegie Mellon   University, Cyrus Daboo, Lawrence Greenfield, Michael Haardt, Kjetil   Torgrim Homme, Arnt Gulbrandsen, Mark Mallett, Alexey Melnikov,   Jeffrey Hutzelman, Philip Guenther, and many others whose names have   been lost during the inexcusably long gestation period of this   document.Authors' Addresses   Tim Showalter   EMail: tjs@psaux.com   Ned Freed (editor)   Sun Microsystems   3401 Centrelake Drive, Suite 410   Ontario, CA  92761-1205   USA   Phone: +1 909 457 4293   EMail: ned.freed@mrochek.comShowalter & Freed           Standards Track                    [Page 15]

RFC 5230               Sieve: Vacation 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.Showalter & Freed           Standards Track                    [Page 16]