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SIEVE Email Filtering Working T. Showalter
Group ??
Internet-Draft N. Freed, Ed.
Expires: October 3, 2005 Sun Microsystems
April 1, 2005
Sieve Email Filtering: Vacation Extension
draft-ietf-sieve-vacation-01
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
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Copyright Notice
Copyright (C) The Internet Society (2005).
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.
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Change History (to be removed prior to publication as an RFC)
Changes from draft-showalter-sieve-vacation-06.txt:
1. Updated to XML source.
2. Added :from parameter.
3. Added :handle parameter.
4. Added more detailed description of :subject parameter
5. Clarified some discussion text.
6. Fixed various minor typos.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Capability Identifier . . . . . . . . . . . . . . . . . . . . 4
3. Vacation Action . . . . . . . . . . . . . . . . . . . . . . . 4
3.1 Days Parameter . . . . . . . . . . . . . . . . . . . . . . 4
3.2 Previous Response Tracking . . . . . . . . . . . . . . . . 5
3.3 Subject and from parameters . . . . . . . . . . . . . . . 6
3.4 MIME Parameter . . . . . . . . . . . . . . . . . . . . . . 6
3.5 Address Parameter and Limiting Replies to Personal
Messages . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.6 Restricting Replies to Automated Processes and Mailing
Lists . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.7 Interaction with Other Sieve Actions . . . . . . . . . . . 7
3.8 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Response Message Generation . . . . . . . . . . . . . . . . . 8
4.1 SMTP MAIL FROM address . . . . . . . . . . . . . . . . . . 8
4.2 Subject Parameter . . . . . . . . . . . . . . . . . . . . 8
4.3 In-Reply-To and References . . . . . . . . . . . . . . . . 9
4.4 From . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.5 To . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.6 Auto-submitted . . . . . . . . . . . . . . . . . . . . . . 9
4.7 Message Body . . . . . . . . . . . . . . . . . . . . . . . 9
5. Relationship to Recommendations for Automatic Responses to
Electronic Mail . . . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1 Normative References . . . . . . . . . . . . . . . . . . . 10
8.2 Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 11
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . 12
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1. Introduction
This is an extension to the Sieve language defined by [RFC3028] for
notification that messages will not be immediately answered.
Conventions for notations are as in [RFC3028] section 1.1.
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", "CAN", and
"MAY" in this document are to be interpreted as defined in [RFC2119].
2. Capability Identifier
Sieve implementations that implement vacation have an identifier of
"vacation" for use with the capability mechanism.
3. Vacation Action
Syntax: 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.
3.1 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. 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.
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
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is used instead.
3.2 Previous Response Tracking
"Vacation" keeps track of all of 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 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.)
Vacation responses are not just per address, but are per address per
set of vacation command arguments. 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, once with the first message, once with the second.
Example: require "vacation";
if header :contains "subject" "cyrus" {
vacation "I'm out -- send mail to cyrus-bugs";
} else {
vacation "I'm out -- call me at 304 555 1212";
}
In the above example, coyote@desert.example.org gets the second
message despite having gotten the first one because separate vaca-
tion responses have been triggered. This behavior is REQUIRED.
The "per set of arguments" described above is intended to ensure that
a respondee gets all of the various possible responses, not merely
the first one. So, if the :subject or :mime parameters would result
in a different message, a different message MUST be sent by the
implementation.
The optional ":handle" parameter can be used to tell the sieve
interpreter to treat two vacation commands 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.
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Example: 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 that one way to implement the necessary mechanism here is to
store a hash of either the current handle and the recipient or, if no
handle is provided, a hash of the generated message content and the
recipient. If a script is changed, implementations MAY reset the
records of who has been responded to and when they have been
responded to.
Implementations are free to limit the number of remembered responses,
provided the limit is no less than 1000. When limiting the number of
tracked responses, implementations SHOULD discard the oldest ones
first.
3.3 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 non-ASCII characters are present.
Implementations SHOULD insert an apppropriate default subject line 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 security
restrictions on what addresses can specified in a ":from" parameter;
it is suggested that values which fail such a security check simply
be ignored rather than causing the vacation action to fail.
3.4 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 (see section 2.4.2.4 of
[RFC3028]).
If the optional :mime parameter is not supplied, the reason string is
considered to be a UTF-8 string.
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3.5 Address Parameter and Limiting Replies to Personal Messages
"Vacation" MUST NOT respond to a message unless the user's email
address is in a "To", "Cc", "Bcc", "Resent-To", "Resent-Cc", or
"Resent-Bcc" line of the original message. Implementations are
assumed to know the user's email address, but users may have
additional addresses beyond the control of the local mail system.
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 in
addition to the addresses that the implementation knows.
3.6 Restricting Replies to Automated Processes and Mailing Lists
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 with a header that
begins with "List-".
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].
3.7 Interaction with Other Sieve Actions
Vacation does not affect Sieve's implicit keep action.
Vacation can only be executed once per script. A script will fail if
two vacation actions are used.
Implementations MUST NOT consider vacation used with discard, keep,
fileinto, or redirect an error.
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3.8 Examples
Here is a simple use of vacation.
Example:
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.
Example: 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.";
}
4. 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.
4.1 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.
4.2 Subject Parameter
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
"Re: " followed by the original subject with all leading occurrence
of the characters "Re: " stripped off.
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4.3 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 must 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 bne changed.
4.4 From
Unless explicitly overridden with a :from parameter, the From field
SHOULD be set to the address of the owner of the Sieve script.
4.5 To
The To field SHOULD be set to the address of the recipient of the
response.
4.6 Auto-submitted
An Auto-Submitted field with a value of "auto-replied" SHOULD be
included in the message header of any vacation message sent.
4.7 Message Body
The body of the message is taken from the reason string in the
vacation command.
5. 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 [RFC3834] makes in
regards to how personal responders should behave.
6. Security Considerations
It is critical that implementations correctly implement the
limitations described above. 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.
Security issues associated with mail auto-responders are fully
discussed in the security consideration section of [RFC3834].
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7. 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
Capability keyword: vacation
Capability arguments: N/A
Standards Track/IESG-approved experimental RFC number: this RFC
Person and email address to contact for further information:
Tim Showalter
E-Mail: tjs@psaux.com
This information should be added to the list of Sieve extensions
given on http://www.iana.org/assignments/sieve-extensions.
8. References
8.1 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.
[RFC3028] Showalter, T., "Sieve: A Mail Filtering Language",
RFC 3028, January 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.
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8.2 Informative References
[RFC2142] Crocker, D., "MAILBOX NAMES FOR COMMON SERVICES, ROLES AND
FUNCTIONS", RFC 2142, May 1997.
Authors' Addresses
Tim Showalter
??
Email: tjs@psaux.com
Ned Freed (editor)
Sun Microsystems
Phone: +1 909 457 4293
Email: ned.freed@mrochek.com
Appendix A. Acknowledgements
This extension is obviously inspired by Eric Allman's vacation
program under Unix. The author owes a great deal to Carnegie Mellon
University, Cyrus Daboo, Lawrence Greenfield, and many others whose
names have been lost during the inexcusably long gestation period of
this document.
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