One document matched: draft-burger-vpim-cc-00.txt
Network Working Group E. Burger
Internet Draft Centigram Communications
Document: draft-burger-vpim-cc-00.txt E. Candell
Category: Standards Track Comverse Network Systems
Expires in six Months June 6, 2000
Critical Content of Internet Mail
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1].
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1.
Abstract
This document describes a mechanism for identifying the critical
content body parts of a multi-part Internet mail message.
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Table of Contents
1.ABSTRACT ...........................................................1
2.CONVENTIONS USED IN THIS DOCUMENT ..................................2
3.INTRODUCTION .......................................................2
4.CONTENT-NOTIFICATION ENTITY ........................................5
4.1. NOTIFY ..........................................................5
4.2. PARTIAL .........................................................5
4.3. IGNORE ..........................................................6
4.4. Other Values ....................................................6
4.5. Notification Precedence .........................................6
5.BACKWARD COMPATIBILITY CONSIDERATIONS ..............................6
6.SECURITY CONSIDERATIONS ............................................7
7.COLLECTED SYNTAX ...................................................7
8.REFERENCES .........................................................7
9.ACKNOWLEDGMENTS ....................................................8
10. AUTHOR'S ADDRESSES ...............................................8
2.
Conventions used in this document
This document refers generically to the sender of a message in the
masculine (he/him/his) and the recipient of the message in the
feminine (she/her/hers). This convention is purely for convenience
and makes no assumption about the gender of a message sender or
recipient.
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 in RFC-2119 [2].
FORMATTING NOTE: Notes, such at this one, provide additional
nonessential information that the reader may skip without missing
anything essential. The primary purpose of these non-essential
notes is to convey information about the rationale of this document,
or to place this document in the proper historical or evolutionary
context. Readers whose sole purpose is to construct a conformant
implementation may skip such information. However, it may be of use
to those who wish to understand why we made certain design choices.
3.
Introduction
This document describes the Critical Content identification for
multi-part Internet mail.
The need for a critical content identification mechanism comes about
because of the internetworking of Internet mail systems with legacy
messaging systems that do not fulfil all of the semantics of
Internet mail. Such legacy systems have a limited ability to render
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all parts of a given message. This document will use the case of an
Internet mail system exchanging electronic messages with a legacy
voice messaging system for illustrative purposes.
Electronic mail has historically been text-centric. Extensions such
as MIME [3] enable the desktop to send and receive multi-part,
multimedia messages. Popular multimedia data types include binary
word processing documents, binary business presentation graphics,
voice, and video.
Voice mail has historically been audio-centric. Many voice
messaging systems only render voice. Extensions such as fax enable
the voice mail system to send and receive fax images as well as
create multi-part voice and fax messages. A few voice mail systems
can render text using text-to-speech or text-to-fax technology.
Although theoretically possible, none can today render video.
An important aspect of the interchange between voice messaging
services and desktop e-mail client applications is that the
rendering capability of the voice messaging platform is often much
less than the rendering capability of a desktop e-mail client. In
the e-mail case, the sender has the expectation that the recipient
receives all components of a multimedia message. This is so even if
the recipient cannot render all body parts. In most cases, the
recipient can either find the appropriate rendering tool or tell the
sender that she cannot read the particular attachment.
This is an important issue. By definition, a MIME-enabled user
agent, conforming to [4] will present or make available all of the
body parts to the recipient. However, a voice mail system may not
be capable of storing non-voice objects. Moreover, the voice mail
system may not be capable of notifying the recipient that there were
undeliverable message parts.
The inability of the receiving system to render a body part is
usually a permanent failure. Retransmission of the message will not
improve the likelihood of a future successful delivery. Contrast
this to the case with normal data delivery. Traditional message
failures, such as a garbled message or disabled link will benefit
from retransmission.
This situation is fundamentally different from normal Internet mail.
In the Internet mail case, either the system delivered the message,
or it didn't. There is no concept of a system partially delivering
a message.
In addition, the sender would not mind if the system did not deliver
non-critical parts of a message. In fact, the sender's user agent
may be silently adding body parts to a message unbeknownst to the
sender. For example, take Microsoft Outlook as a user agent.
Outlook often will attach a TNEF section or other body parts. If the
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receiving system rejected the message because it could not render
TNEF, the sender would be understandably confused and upset.
Thus, there is a need for a method of indicating to a Mail Transfer
Agent (MTA) or User Agent (UA) that the sender considers parts of a
message to be critical. From the sender's perspective, he would not
consider the message delivered if the system did not deliver the
critical parts.
One method of indicating critical content of a message is to define
a profile. The profile defines discard rules based on knowledge of
the user population for silently deleting body parts. Citing the
example above, a voice profile can easily declare that MTAs or UAs
can silently delete TNEF data and yet consider the message
successfully delivered. This is, in fact, the approach originally
proposed for VPIMv3 [5].
Since one aspect of the issue is deciding when to notify the sender
that the system cannot deliver part of a message, one could use a
partial non-delivery notification mechanism [6] to indicate a
problem with delivering a given body part. However, this requires
the user request a MDN. Moreover, the sender will receive PNDN
failures for objects the sender may not be aware he is sending. An
example would be the TNEF part.
Summarizing the needs, we need a mechanism that will let the sender
or sender's UA mark body parts he considers critical to the message
that the system must deliver. The mechanism MUST NOT burden the
sender with failure notifications for non-critical body parts. The
mechanism MUST conform to the general notification status request
mechanism for positive or negative notification. When requested,
the mechanism MUST indicate to the sender when a receiving system
cannot deliver a critical body part.
In short, we need a method of indicating what sort of delivery
notification the sender requires on a per-body part basis.
This document describes a Critical Content marking mechanism that
satisfies these needs. Following the format for Internet message
bodies [3], this document introduces the Content-Notification body
part header. Values for this header are NOTIFY, PARTIAL, or IGNORE.
The receiving MTA or UA will generate a DSN or PNDN if it receives a
request for notification and the (non-)delivery status of the parts
marked NOTIFY meet the criteria for notification. Likewise, the
receiving UA will generate a MDN or MNDN if it receives a request
for notification and the (non-)delivery status of the parts marked
NOTIFY meet the criteria for notification.
<<<EDITOR'S NOTE: We don't have an ID for MNDN yet, but it will look
like PNDN. Stay tuned.>>>
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4.
Content-Notification Entity
The Content-Notification field is a MIME body part header inserted
by the sending UA to indicate to the receiving MTA or UA whether to
consider this body part when generating a (non-)delivery message.
If the value of the field is IGNORE, the receiving MTA or UA MUST
NOT generate a notification. If the value of the field is NOTIFY,
the receiving MTA or UA MUST generate a notification, based on the
normal notification request mechanisms. Normal notification request
mechanisms include the SMTP RCPT NOTIFY command [7] and the
Disposition-Notification-To header [8].
The terms "entity" and "body part" have the meanings defined in [3].
The next sections examine the actions taken by an MTA or UA given
the different values of Content-Notification.
NOTE: This implies that the MTA must examine the entire message on
receipt to determine whether it needs to generate a notification.
However, the MTA need not examine the message if it knows it can
store and forward all media types. Said differently, an Internet e-
mail MTA can, by default, handle any arbitrary MIME-encapsulated
type. Some voice mail systems, on the other hand, cannot even store
binary attachments, such as application/ms-word. The voice mail
MTA, in this example, would be scanning for non-renderable body
parts anyway.
4.1. NOTIFY
"Content-Notification: NOTIFY" signifies that this body part is
critical to the sender. The sender wishes to receive notification
reports for this body part.
If the receiving system cannot render or store a body part marked
NOTIFY, then the entire message has failed. In this case, the
receiving system MUST take the appropriate failure action.
NOTE: We say "appropriate action", because the sender may have
suppressed all notifications. In this case, the appropriate action
is to simply discard the message.
4.2. PARTIAL
"Content-Notification: PARTIAL" signifies that the sender wishes to
receive notification reports for this body part.
If the receiving system cannot render or store a body part marked
PARTIAL, the receiving system MUST take the appropriate failure
action. It is important to note that if the system is successful in
delivering other critical body parts, then the message delivery is
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successful. In this situation, the receiving system MUST return a
partial non-delivery notification [6].
4.3. IGNORE
"Content-Notification: IGNORE" signifies that the sender does not
care about notification reports for this body part.
If the receiving system cannot render or store a body part marked
IGNORE, the receiving system may silently delete the body part. The
receiving system MUST NOT return a delivery failure, unless parts
marked PARTIAL or NOTIFY have also failed.
4.4. Other Values
The receiving system MUST treat unrecognized values as PARTIAL.
This is to provide backward compatibility with future uses of the
Content-Notification entity.
<<<ALTERNATIVES:
IGNORE: If I don't recognize something, ignore it!
NOTIFY: Future values are more likely to involve some sort of
notification, rather than non-notification. However, if the
notifications are more sophisticated than NOTIFY, senders may be
miffed they didn't get the processing they expected.
Reject the Message: This would be too extreme! Yes, it would weed
out non-conformant sending UAs, but this would really piss off
users.
So far, we have one vote for IGNORE, as that would be compatible
with VPIMv2.
We have one vote for PARTIAL, as that would provide forward-
compatibility with future uses of Content-Notification.
We expect this to be a point of discussion on the list.
End of ALTERNATIVES>>>
4.5. Notification Precedence
<<<We'll fill-in this in the next draft.>>>
5.
Backward Compatibility Considerations
If there are no Content-Notification entities in the message, the
default value for Content-Notification is NOTIFY. The standard
notification mechanisms work for sending user agents (UA) that do
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not know about the content notification entity. All body parts are
critical, because they have the default marking of NOTIFY.
If there is at least one Content-Notification entity in the message,
the default value for unspecified body parts is IGNORE. The
philosophy is that UAs, especially manually constructed messages,
will explicitly mark the critical body parts.
NOTE: We could choose the default value for Content-Notification to
be IGNORE. This would make VPIMv2 automatically compliant with this
document, as VPIMv2 has provision to silently delete undeliverable
parts. However, VPIMv2 systems should not be receiving arbitrary e-
mail from the Internet. If they do, they should be compliant with
this series of documents. By defaulting to NOTIFY, this draft is
compliant with the rest of the Internet infrastructure.
6.
Security Considerations
We anticipate no new security issues beyond those already addressed
by the notification RFCs.
7.
Collected Syntax
The format of the collected syntax is in accordance with the ABNF of
[9]. Note that per RFC 2045, none of the strings are case
sensitive.
"Content-Notification" ":" notification-type CRLF
notification-type = "NOTIFY" / "PARTIAL" / "IGNORE"
8.
References
1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
2 Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
3 Freed, N. and Borenstein, N., "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, Innosoft and First Virtual, November 1996.
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4 Freed, N. and Borenstein, N., "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, Innosoft and
First Virtual, November 1996.
5 Vaudreuil, G. and Parsons, G., "Voice Profile for Internet Mail -
version 3", <draft-ema-vpimv3-00.txt>, Work in Progress, expired.
6 Burger, E., "Partial Non-Delivery Notification", Work in
Progress, draft-ema-burger-pndn-01.txt, March 2000.
7 Moore, K., "SMTP Service Extension for Delivery Status
Notifications", RFC 1981, University of Tennessee, January 1996.
8 Fajman, R., "An Extensible Message Format for Message Disposition
Notifications", RFC 2298, National Institutes of Health, March
1998.
9 Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, Internet Mail Consortium and
Demon Internet Ltd., November 1997.
9.
Acknowledgments
Coming soon!
10.
Author's Addresses
Eric Burger
Centigram Communications Corporation
Maryland Technology Center
1375 Piccard Dr., MS 150I
Rockville, MD 20850-4311
USA
Phone: +1 301/212-3320
Email: e.burger@ieee.org
Emily Candell
Comverse Network Systems
200 Quannapowitt Pkwy.
Wakefield, MA 01880
USA
Phone: +1 781/213-2324
Email: emily@comversens.com
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