Sieve working group R. George
Internet-Draft B. Leiba
Intended status: Informational Huawei Technologies
Expires: December 25, 2010 A. Melnikov
Isode Limited
June 23, 2010
Sieve Email Filtering: Use of Presence Information with Auto Responder
functionality
draft-ietf-sieve-autoreply-00
Abstract
This document describes how the Sieve email filtering language, along
with some extensions, can be used to create automatic replies to
incoming electronic mail messages based on the address book and
presence information of the recipient.
Status of this Memo
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the Trust Legal Provisions and are provided without warranty as
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. How To Create Auto Replies . . . . . . . . . . . . . . . . . . 3
3. Example Use Cases for Auto Replies . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
6. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
This document describes how the Sieve email filtering language
[RFC5228], along with some extensions [RFC5230] [RFC5435]
[I-D.ietf-sieve-external-lists] [I-D.ietf-sieve-notify-presence]
[I-D.ietf-sieve-vacation-seconds] can be used to generate automatic
replies to incoming electronic mail messages based on the presence
information of the recipient. This can be used, for example, to
inform the sender that messages will not be answered immediately
because the recipient is busy or away.
The auto-reply message can additionally be based on information about
the sender from the recipient's address book, sub-lists therefrom, or
other lists available to the recipient, so that different senders
might get different responses. The recipient can create separate
rules for friends, family members, colleagues, and so on.
This can be used in mail filtering software, email-based information
services, and other automatic responder situations. There are many
programs currently in use that automatically respond to email. Some
of them send many useless or unwanted responses, or send responses to
inappropriate addresses. The mechanism described herein will help to
avoid those problems (but see the discussion in Section 4).
Implementations need to take care of tracking previous messages
received from the same sender and they will start or stop sending
responses as the presence status of the recipient changes.
[[Barry's question: One thing this makes me think of is whether we
want the ability to extract information from an external list. For
instance, it'd be nice to be able to go into the recipient's address
book for the sender's real name, or for a personalized message for
the sender. Not all lists will support this; should it be possible,
for lists that do?]]
2. How To Create Auto Replies
When an email message arrives, the Sieve script can use the
notify_method_capability of the Notify extension [RFC5435] to check
the recipient's presence information. The Notify-presence extension
[I-D.ietf-sieve-notify-presence] makes additional presence, such as
"away" and "do not disturb" status, available. The script can use
the External-lists extension [I-D.ietf-sieve-external-lists] to look
the sender up in the recipient's address book or other list. If the
information retrieved warrants an auto-reply message, the message can
then be composed based on that information.
The Vacation extension [RFC5230] provides an easy way to send the
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auto-reply message to the sender, as it automatically keeps track of
the automatic replies and attempts to avoid excessive messages and
mail loops. The Vacation-seconds extension
[I-D.ietf-sieve-vacation-seconds] allows auto-replies to be sent this
way more frequently than once per day, when that's appropriate.
(Alternatively, the script can use the Notify extension,[RFC5435] and
it can use that to send a notification by a means other than email.)
Personal and Group Responders can refuse to generate responses except
to known correspondents or addresses otherwise known to the
recipient. Such responders can also generate different kinds of
responses for "trusted" vs "untrusted" addresses. This might be
useful, for instance, to avoid inappropriate disclosure of personal
or confidential information to arbitrary addresses.
3. Example Use Cases for Auto Replies
1. In this example, we check that the envelope "from" is in the
recipient's address book [I-D.ietf-sieve-external-lists] and that
the recipient's presence shows "extended
away".[I-D.ietf-sieve-notify-presence] If both of those are
true, the "vacation" action [RFC5230] is used to send an auto-
reply, making sure we don't reply to the same sender more than
once every half hour.[I-D.ietf-sieve-vacation-seconds] The
variables extension [RFC5229] is used to extract the value of the
recipient's natural-language presence status message, which will
be used in the response to the sender.
require ["extlists", "enotify", "variables", "vacation-seconds"];
if allof (
envelope :list "from" "tag:example.com,2009-05-28:AddrBook",
notify_method_capability "xmpp:me@example.com" "show" "xa"
) {
# :matches "*" is used here to extract the value
if notify_method_capability :matches
"xmpp:myjid@example.com" "status" "*" {
set "resp_msg" "${1}";
} else {
set "resp_msg" "Away for a while, without access to email.";
}
vacation :handle "ext-away" :seconds 1800 "${resp_msg}";
}
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2. In the next example, we'll check several lists or sublists, auto-
replying to everyone, but sending more detail about the
recipient's status to senders who are found in the recipient's
address book, and still more detail to those in the "family" and
"friends" lists.
require ["extlists", "enotify", "vacation-seconds"];
if envelope :list "from" ["tag:example.com,2009-05-28:family",
"tag:example.com,2009-05-28:friends"]
{
if notify_method_capability "xmpp:me@example.com" "show" "away"
{
vacation :handle "away" :seconds 600
"I'm away for now, but I'll be back soon.";
}
elsif notify_method_capability "xmpp:me@example.com" "show" "dnd"
{
vacation :handle "dnd" :seconds 1800
"I'm not to be disturbed. I'll check mail later.";
}
elsif notify_method_capability "xmpp:me@example.com" "show" "xa"
{
vacation :handle "ext-away" :seconds 3600
"I'm away for a while, without access to email.";
}
elsif notify_method_capability "xmpp:me@example.com" "busy" "yes"
{
vacation :handle "busy" :seconds 1800
"I'm very busy, but might check email now and then.";
}
}
elsif envelope :list "from" "tag:example.com,2009-05-28:AddrBook"
{
if notify_method_capability "xmpp:me@example.com" "show"
["away", "dnd", "xa"]
{
vacation :handle "away" :seconds 3600
"I'm not available to respond to email.";
}
}
else # the sender is not in the address book
{
vacation :handle "catchall" :days 1
"I got your message, and might read it eventually.";
}
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3. For this example, if the sender is a work colleague and the
recipient is on extended away status, then reply with a message
giving alternative contact information. The message might also
include details about the reason for the absence, or other
personal or confidential information that shouldn't be shared
with senders who aren't associated with the recipient's company.
require ["extlists", "enotify", "vacation"];
if envelope :list "from" "tag:example.com,2009-05-28:co-workers"
{
if notify_method_capability "xmpp:me@example.com" "show" "xa"
{
vacation :handle "bigtrip" :days 3
"I'm on an extended business trip to Texas for the Foo
project. Contact my backup, Susan <susan@example.com>,
or call my assistant on +1 666 555 1234 if you urgently
need to contact me.";
}
}
4. This example is used to send an acknowledgment to every message
received. A :seconds value of zero is used to reply to every
message, with no removal of duplicates to the same sender. This
requires that the Sieve engine allow an interval of zero; if it
does not, and it imposes a minimum value, not every message will
receive an auto-reply.
require ["extlists", "vacation-seconds"];
if not envelope :list "from" "tag:example.com,2009-05-28:staff"
{
vacation :handle "auto-resp" :seconds 0
"Your request has been received. A service
representative will contact you as soon as
possible, usually within one business day.";
}
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5. This example uses the same structure to automatically send a copy
of each incoming message to the recipient's backup, if the sender
is a customer contact or co-worker, or if the message's subject
includes the word "urgent".
require ["extlists", "enotify"];
if anyof (
envelope :list "from" ["tag:example.com,2009-05-28:customers",
"tag:example.com,2009-05-28:co-workers"],
header :contains "subject" "urgent"
) {
if notify_method_capability "xmpp:me@example.com" "show" "xa"
{
redirect "susan@example.com"; # send a copy to my backup
keep; # also keep a copy for myself
}
}
}
4. Security Considerations
See the referenced specifications, below for discussion of security
considerations for Sieve scripts in general, and for each of the
extensions in particular.
This document describes how to set up a system that creates automatic
replies in an intelligent way. Despite the "intelligence", errors in
scripts can result in too many auto-reply messages, especially when
the reply interval is minimal (using the "notify" action, or the
"vacation" action with a small value for ":seconds").
Despite the "intelligence", too, errors in scripts can result in
private information getting to senders inappropriately. In example 3
in Section 3, for instance, if the :list test checks the wrong list,
or none at all, information about the recipient's business trip might
be send to someone who has no need to know about it, and shouldn't.
Even without errors in scripts, a sender who recognizes that auto-
replies are dependent upon the recipient's presence can use that fact
to probe the presence information. One result of that can be that
the sender discerns changes in the recipient's presence that the
sender would normally not be allowed to see, making this an
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unintentional back door into the user's presence information.
Another result is that this can create a "covert channel", allowing
the recipient to send information to a sender by changing his
presence information, his address book, and/or his Sieve script
(though in this regard, the exposure is comparable to any other case
of shared presence information).
Finally, users of any auto-reply mechanism should really think about
whether automatic replies are necessary, and at what interval they
make sense when they are. Email is not Instant Messaging, and
senders generally expect that replies might take a while. Consider
whether it's truly important to tell people that you'll read their
mail in an hour or so, or whether that can just be taken as how email
works. There are times when this makes sense, but let's not use it
to exacerbate information overload.
5. IANA Considerations
There are no IANA actions required by this document.
6. Normative References
[I-D.ietf-sieve-notify-presence]
George, R. and B. Leiba, "Sieve Notification Using
Presence Information",
draft-ietf-sieve-notify-presence-00 (work in progress),
June 2010.
[I-D.ietf-sieve-vacation-seconds]
George, R. and B. Leiba, "Sieve Vacation Extension:
"Seconds" parameter", draft-ietf-sieve-vacation-seconds-00
(work in progress), June 2010.
[I-D.ietf-sieve-external-lists]
Melnikov, A. and B. Leiba, "Sieve Extension: Externally
Stored Lists", draft-ietf-sieve-external-lists-02 (work in
progress), May 2010.
[RFC5228] Guenther, P. and T. Showalter, "Sieve: An Email Filtering
Language", RFC 5228, January 2008.
[RFC5229] Homme, K., "Sieve Email Filtering: Variables Extension",
RFC 5229, January 2008.
[RFC5230] Showalter, T. and N. Freed, "Sieve Email Filtering:
Vacation Extension", RFC 5230, January 2008.
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[RFC5435] Melnikov, A., Leiba, B., Segmuller, W., and T. Martin,
"Sieve Email Filtering: Extension for Notifications",
RFC 5435, January 2009.
Authors' Addresses
Robins George
Huawei Technologies
Huawei Base, Bantian, Longgang District
Shenzhen, Guangdong 518129
P. R. China
Phone: +86-755-28788314
Email: robinsg@huawei.com
Barry Leiba
Huawei Technologies
Phone: +1 646 827 0648
Email: barryleiba@computer.org
URI: http://internetmessagingtechnology.org/
Alexey Melnikov
Isode Limited
5 Castle Business Village, 36 Station Road
Hampton, Middlesex TW12 2BX
UK
Email: Alexey.Melnikov@isode.com
URI: http://www.melnikov.ca/
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