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Network Working Group T. Showalter Request for Comments: 5230 Category: Standards Track N. Freed, Ed.

                                                      Sun Microsystems
                                                          January 2008
             Sieve Email Filtering: Vacation Extension

Status 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.


 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 2008

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
 2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
 3.  Capability Identifier  . . . . . . . . . . . . . . . . . . . .  3
 4.  Vacation Action  . . . . . . . . . . . . . . . . . . . . . . .  3
   4.1.  Days Parameter . . . . . . . . . . . . . . . . . . . . . .  3
   4.2.  Previous Response Tracking . . . . . . . . . . . . . . . .  4
   4.3.  Subject and From Parameters  . . . . . . . . . . . . . . .  6
   4.4.  MIME Parameter . . . . . . . . . . . . . . . . . . . . . .  6
   4.5.  Address Parameter and Limiting Replies to Personal
         Messages . . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.6.  Restricting Replies to Automated Processes and Mailing
         Lists  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   4.7.  Interaction with Other Sieve Actions . . . . . . . . . . .  8
   4.8.  Examples . . . . . . . . . . . . . . . . . . . . . . . . .  9
 5.  Response Message Generation  . . . . . . . . . . . . . . . . .  9
   5.1.  SMTP MAIL FROM Address . . . . . . . . . . . . . . . . . .  9
   5.2.  Date . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   5.3.  Subject  . . . . . . . . . . . . . . . . . . . . . . . . . 10
   5.4.  From . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   5.5.  To . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   5.6.  Auto-Submitted . . . . . . . . . . . . . . . . . . . . . . 10
   5.7.  Message Body . . . . . . . . . . . . . . . . . . . . . . . 10
   5.8.  In-Reply-To and References . . . . . . . . . . . . . . . . 10
 6.  Relationship to Recommendations for Automatic Responses to
     Electronic Mail  . . . . . . . . . . . . . . . . . . . . . . . 11
 7.  Internationalization Considerations  . . . . . . . . . . . . . 11
 8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
 9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
   10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
   10.2. Informative References . . . . . . . . . . . . . . . . . . 13
 Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 15

Showalter & Freed Standards Track [Page 2] RFC 5230 Sieve: Vacation Extension January 2008

1. 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

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

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
 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
 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 sends mail to twice, once with the subject "Cyrus bug"
 and once with the subject "come over for dinner", and has the script shown below, 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, 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
 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 sends
 mail to twice, one with the subject
 "lunch?" and once with the subject "dinner?", and has the script shown below, will only receive a single response.  (Which
 response is sent depends on the order in which the messages are
 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.  One

Showalter & 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
 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
  1. -foo
 I'm at the beach relaxing.  Mmmm, surf...
  1. -foo

Content-Type: text/html; charset=us-ascii

 <HTML><HEAD><TITLE>How to relax</TITLE>
 <BODY><P>I'm at the <A HREF="beach.gif">beach</A> relaxing.
 Mmmm, <A HREF="ocean.gif">surf</A>...
  1. -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 2008

4.6. 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 2008

4.8. Examples

 Here is a simple use of vacation.
 require "vacation";
 vacation :days 23 :addresses ["",
 "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
 require "vacation";
 if header :contains "from" "" {
     redirect "";
 } 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
 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 2008

5.3. 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

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 2008

6. 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

Showalter & Freed Standards Track [Page 11] RFC 5230 Sieve: Vacation Extension January 2008

 require "vacation";
 if address :matches "from" "*"
     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:
 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 5230

Showalter & Freed Standards Track [Page 12] RFC 5230 Sieve: Vacation Extension January 2008

 Contact address: The Sieve discussion list <>
 This information has been added to the list of Sieve extensions given

10. References

10.1. 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.
            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 2008

Appendix 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

Authors' Addresses

 Tim Showalter
 Ned Freed (editor)
 Sun Microsystems
 3401 Centrelake Drive, Suite 410
 Ontario, CA  92761-1205
 Phone: +1 909 457 4293

Showalter & Freed Standards Track [Page 15] RFC 5230 Sieve: Vacation Extension January 2008

Full Copyright Statement

 Copyright (C) The IETF Trust (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.
 This document and the information contained herein are provided on an

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 Copies of IPR disclosures made to the IETF Secretariat and any
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Showalter & Freed Standards Track [Page 16]

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