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Network Working Group R. Fajman
Request for Comments: 2298 National Institutes of Health
Category: Standards Track March 1998
An Extensible Message Format
for Message Disposition Notifications
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.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
Abstract
This memo defines a MIME content-type that may be used by a mail user
agent (UA) or electronic mail gateway to report the disposition of a
message after it has been sucessfully delivered to a recipient. This
content-type is intended to be machine-processable. Additional
message headers are also defined to permit Message Disposition
Notifications (MDNs) to be requested by the sender of a message. The
purpose is to extend Internet Mail to support functionality often
found in other messaging systems, such as X.400 and the proprietary
"LAN-based" systems, and often referred to as "read receipts,"
"acknowledgements," or "receipt notifications." The intention is to
do this while respecting the privacy concerns that have often been
expressed when such functions have been discussed in the past.
Because many messages are sent between the Internet and other
messaging systems (such as X.400 or the proprietary "LAN-based"
systems), the MDN protocol is designed to be useful in a multi-
protocol messaging environment. To this end, the protocol described
in this memo provides for the carriage of "foreign" addresses, in
addition to those normally used in Internet Mail. Additional
attributes may also be defined to support "tunneling" of foreign
notifications through Internet Mail.
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Table of Contents
1. Introduction ............................................ 2
2. Requesting Message Disposition Notifications ............ 3
3. Format of a Message Disposition Notification ............ 7
4. Timeline of events ...................................... 17
5. Conformance and Usage Requirements ...................... 18
6. Security Considerations ................................. 19
7. Collected Grammar ....................................... 20
8. Guidelines for Gatewaying MDNs .......................... 22
9. Example ................................................. 24
10. IANA Registration Forms ................................. 25
11. Acknowledgments ......................................... 26
12. References .............................................. 26
13. Author's Address ........................................ 27
14. Copyright ............................................... 28
1. Introduction
This memo defines a MIME content-type [5] for message disposition
notifications (MDNs). An MDN can be used to notify the sender of a
message of any of several conditions that may occur after successful
delivery, such as display of the message contents, printing of the
message, deletion (without display) of the message, or the
recipient's refusal to provide MDNs. The "message/disposition-
notification" content-type defined herein is intended for use within
the framework of the "multipart/report" content type defined in RFC
1892 [7].
This memo defines the format of the notifications and the RFC 822
headers used to request them.
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.
1.1 Purposes
The MDNs defined in this memo are expected to serve several purposes:
(a) Inform human beings of the disposition of messages after
succcessful delivery, in a manner which is largely independent
of human language;
(b) Allow mail user agents to keep track of the disposition of
messages sent, by associating returned MDNs with earlier message
transmissions;
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(c) Convey disposition notification requests and disposition
notifications between Internet Mail and "foreign" mail systems
via a gateway;
(d) Allow "foreign" notifications to be tunneled through a MIME-
capable message system and back into the original messaging
system that issued the original notification, or even to a third
messaging system;
(e) Allow language-independent, yet reasonably precise, indications
of the disposition of a message to be delivered.
1.2 Requirements
These purposes place the following constraints on the notification
protocol:
(a) It must be readable by humans, as well as being machine-
parsable.
(b) It must provide enough information to allow message senders (or
their user agents) to unambiguously associate an MDN with the
message that was sent and the original recipient address for
which the MDN is issued (if such information is available), even
if the message was forwarded to another recipient address.
(c) It must also be able to describe the disposition of a message
independent of any particular human language or of the
terminology of any particular mail system.
(d) The specification must be extensible in order to accomodate
future requirements.
2. Requesting Message Disposition Notifications
Message disposition notifications are requested by including a
Disposition-Notification-To header in the message. Further
information to be used by the recipient's UA in generating the MDN
may be provided by including Original-Recipient and/or Disposition-
Notification-Options headers in the message.
2.1 The Disposition-Notification-To Header
A request that the receiving user agent issue message disposition
notifications is made by placing a Disposition-Notification-To header
into the message. The syntax of the header, using the ABNF of RFC
822 [2], is
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mdn-request-header = "Disposition-Notification-To" ":" 1#mailbox
The mailbox token is as specified in RFC 822 [2].
The presence of a Disposition-Notification-To header in a message is
merely a request for an MDN. The recipients' user agents are always
free to silently ignore such a request. Alternatively, an explicit
denial of the request for information about the disposition of the
message may be sent using the "denied" disposition in an MDN.
An MDN MUST NOT itself have a Disposition-Notification-To header.
An MDN MUST NOT be generated in response to an MDN.
At most one MDN may be issued on behalf of each particular recipient
by their user agent. That is, once an MDN has been issued on behalf
of a recipient, no further MDNs may be issued on behalf of that
recipient, even if another disposition is performed on the message.
However, if a message is forwarded, an MDN may been issued for the
recipient doing the forwarding and the recipient of the forwarded
message may also cause an MDN to be generated.
While Internet standards normally do not specify the behavior of user
interfaces, it is strongly recommended that the user agent obtain the
user's consent before sending an MDN. This consent could be obtained
for each message through some sort of prompt or dialog box, or
globally through the user's setting of a preference. The user might
also indicate globally that MDNs are never to be sent or that a
"denied" MDN is always sent in response to a request for an MDN.
MDNs SHOULD NOT be sent automatically if the address in the
Disposition-Notification-To header differs from the address in the
Return-Path header (see RFC 822 [2]). In this case, confirmation
from the user SHOULD be obtained, if possible. If obtaining consent
is not possible (e.g., because the user is not online at the time),
then an MDN SHOULD NOT be sent.
Confirmation from the user SHOULD be obtained (or no MDN sent) if
there is no Return-Path header in the message, or if there is more
than one distinct address in the Disposition-Notification-To header.
The comparison of the addresses should be done using only the addr-
spec (local-part "@" domain) portion, excluding any phrase and route.
The comparison MUST be case-sensitive for the local-part and case-
insensitive for the domain part.
If the message contains more than one Return-Path header, the
implementation may pick one to use for the comparison, or treat the
situation as a failure of the comparison.
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The reason for not automatically sending an MDN if the comparison
fails or more than one address is specified is to reduce the
possibilities for mail loops and use of MDNs for mail bombing.
A message that contains a Disposition-Notification-To header SHOULD
also contain a Message-ID header as specified in RFC 822 [2]. This
will permit automatic correlation of MDNs with original messages by
user agents.
If it is desired to request message disposition notifications for
some recipients and not others, two copies of the message should be
sent, one with an Disposition-Notification-To header and one without.
Many of the other headers of the message (e.g., To, cc) will be the
same in both copies. The recipients in the respective message
envelopes determine for whom message disposition notifications are
requested and for whom they are not. If desired, the Message-ID
header may be the same in both copies of the message. Note that
there are other situations (e.g., bcc) in which it is necessary to
send multiple copies of a message with slightly different headers.
The combination of such situations and the need to request MDNs for a
subset of all recipients may result in more than two copies of a
message being sent, some with a Disposition- Notification-To header
and some without.
Messages posted to newsgroups SHOULD NOT have a Disposition-
Notification-To header.
2.2 The Disposition-Notification-Options Header
Future extensions to this specification may require that information
be supplied to the recipient's UA for additional control over how and
what MDNs are generated. The Disposition-Notification-Options header
provides an extensible mechanism for such information. The syntax of
this header, using the ABNF of RFC 822 [2], is
Disposition-Notification-Options =
"Disposition-Notification-Options" ":"
disposition-notification-parameters
disposition-notification-parameters = parameter *(";" parameter)
parameter = attribute "=" importance "," 1#value
importance = "required" / "optional"
The definitions of attribute and value are as in the definition of
the Content-Type header in RFC 2045 [4].
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An importance of "required" indicates that interpretation of the
parameter is necessary for proper generation of an MDN in response to
this request. If a UA does not understand the meaning of the
parameter, it MUST NOT generate an MDN with any disposition type
other than "failed" in response to the request. An importance of
"optional" indicates that a UA that does not understand the meaning
of this parameter MAY generate an MDN in response anyway, ignoring
the value of the parameter.
No parameters are defined in this specification. Parameters may be
defined in the future by later revisions or extensions to this
specification. Parameter attribute names beginning with "X-" will
never be defined as standard names; such names are reserved for
experimental use. MDN parameter names not beginning with "X-" MUST
be registered with the Internet Assigned Numbers Authority (IANA) and
described in a standards-track RFC or an experimental RFC approved by
the IESG. See Section 10 for a registration form.
If a required parameter is not understood or contains some sort of
error, the receiving UA SHOULD issue an MDN with a disposition type
of "failed" (see Section 3.2.6) and include a Failure field (see
Section 3.2.7) that further describes the problem. MDNs with the a
disposition type of "failed" and a "Failure" field MAY also be
generated when other types of errors are detected in the parameters
of the Disposition-Notification-Options header.
However, an MDN with a disposition type of "failed" MUST NOT be
generated if the user has indicated a preferance that MDNs are not to
be sent. If user consent would be required for an MDN of some other
disposition type to be sent, user consent SHOULD also be obtained
before sending an MDN with a disposition type of "failed".
2.3 The Original-Recipient Header
Since electronic mail addresses may be rewritten while the message is
in transit, it is useful for the original recipient address to be
made available by the delivering MTA. The delivering MTA may be able
to obtain this information from the ORCPT parameter of the SMTP RCPT
TO command, as defined in RFC 1891 [8]. If this information is
available, the delivering MTA SHOULD insert an Original-Recipient
header at the beginning of the message (along with the Return-Path
header). The delivering MTA MAY delete any other Original-Recipient
headers that occur in the message. The syntax of this header, using
the ABNF of RFC 822 [2], is as follows
original-recipient-header =
"Original-Recipient" ":" address-type ";" generic-address
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The address-type and generic-address token are as as specified in the
description of the Original-Recipient field in section 3.2.3.
The purpose of carrying the original recipient information and
returning it in the MDN is to permit automatic correlation of MDNs
with the original message on a per-recipient basis.
2.4 Use with the Message/Partial Content Type
The use of the headers Disposition-Notification-To, Disposition-
Notification-Options, and Original-Recipient with the MIME
Message/partial content type (RFC 2046 [5]) requires further
definition.
When a message is segmented into two or more message/partial
fragments, the three headers mentioned in the above paragraph SHOULD
be placed in the "inner" or "enclosed" message (using the terms of
RFC 2046 [5]). These headers SHOULD NOT be used in the headers of
any of the fragments themselves.
When the multiple message/partial fragments are reassembled, the
following applies. If these headers occur along with the other
headers of a message/partial fragment message, they pertain to an MDN
to be generated for the fragment. If these headers occur in the
headers of the "inner" or "enclosed" message (using the terms of RFC
2046 [5]), they pertain to an MDN to be generated for the reassembled
message. Section 5.2.2.1 of RFC 2046 [5]) is amended to specify
that, in addition to the headers specified there, the three headers
described in this specification are to be appended, in order, to the
headers of the reassembled message. Any occurances of the three
headers defined here in the headers of the initial enclosing message
must not be copied to the reassembled message.
3. Format of a Message Disposition Notification
A message disposition notification is a MIME message with a top-
level content-type of multipart/report (defined in RFC 1892 [7]).
When a multipart/report content is used to transmit an MDN:
(a) The report-type parameter of the multipart/report content is
"disposition-notification".
(b) The first component of the multipart/report contains a human-
readable explanation of the MDN, as described in RFC 1892 [7].
(c) The second component of the multipart/report is of content-type
message/disposition-notification, described in section 3.1 of
this document.
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(d) If the original message or a portion of the message is to be
returned to the sender, it appears as the third component of the
multipart/report. The decision of whether or not to return the
message or part of the message is up to the UA generating the
MDN. However, in the case of encrypted messages requesting
MDNs, encrypted message text MUST be returned, if it is returned
at all, only in its original encrypted form.
NOTE: For message dispostion notifications gatewayed from
foreign systems, the headers of the original message may not be
available. In this case the third component of the MDN may be
omitted, or it may contain "simulated" RFC 822 headers which
contain equivalent information. In particular, it is very
desirable to preserve the subject and date fields from the
original message.
The MDN MUST be addressed (in both the message header and the
transport envelope) to the address(es) from the Disposition-
Notification-To header from the original message for which the MDN is
being generated.
The From field of the message header of the MDN MUST contain the
address of the person for whom the message disposition notification
is being issued.
The envelope sender address (i.e., SMTP MAIL FROM) of the MDN MUST be
null (<>), specifying that no Delivery Status Notification messages
or other messages indicating successful or unsuccessful delivery are
to be sent in response to an MDN.
A message disposition notification MUST NOT itself request an MDN.
That is, it MUST NOT contain a Disposition-Notification-To header.
The Message-ID header (if present) for an MDN MUST be different from
the Message-ID of the message for which the MDN is being issued.
A particular MDN describes the disposition of exactly one message for
exactly one recipient. Multiple MDNs may be generated as a result of
one message submission, one per recipient. However, due to the
circumstances described in Section 2.1, MDNs may not be generated for
some recipients for which MDNs were requested.
3.1 The message/disposition-notification content-type
The message/disposition-notification content-type is defined as
follows:
MIME type name: message
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MIME subtype name: disposition-notification
Optional parameters: none
Encoding considerations: "7bit" encoding is sufficient and
MUST be used to maintain readability
when viewed by non-MIME mail
readers.
Security considerations: discussed in section 6 of this memo.
The message/disposition-notification report type for use in the
multipart/report is "disposition-notification".
The body of a message/disposition-notification consists of one or
more "fields" formatted according to the ABNF of RFC 822 header
"fields" (see [2]). Using the ABNF of RFC 822, the syntax of the
message/disposition-notification content is as follows:
disposition-notification-content = [ reporting-ua-field CRLF ]
[ mdn-gateway-field CRLF ]
[ original-recipient-field CRLF ]
final-recipient-field CRLF
[ original-message-id-field CRLF ]
disposition-field CRLF
*( failure-field CRLF )
*( error-field CRLF )
*( warning-field CRLF )
*( extension-field CRLF )
3.1.1 General conventions for fields
Since these fields are defined according to the rules of RFC 822 [2],
the same conventions for continuation lines and comments apply.
Notification fields may be continued onto multiple lines by beginning
each additional line with a SPACE or HTAB. Text which appears in
parentheses is considered a comment and not part of the contents of
that notification field. Field names are case-insensitive, so the
names of notification fields may be spelled in any combination of
upper and lower case letters. Comments in notification fields may
use the "encoded-word" construct defined in RFC 2047 [6].
3.1.2 "*-type" subfields
Several fields consist of a "-type" subfield, followed by a semi-
colon, followed by "*text". For these fields, the keyword used in
the address-type or MTA-type subfield indicates the expected format
of the address or MTA-name that follows.
The "-type" subfields are defined as follows:
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(a) An "address-type" specifies the format of a mailbox address.
For example, Internet Mail addresses use the "rfc822" address-
type.
address-type = atom
(b) An "MTA-name-type" specifies the format of a mail transfer
agent name. For example, for an SMTP server on an Internet
host, the MTA name is the domain name of that host, and the
"dns" MTA-name-type is used.
mta-name-type = atom
Values for address-type and mta-name-type are case-insensitive. Thus
address-type values of "RFC822" and "rfc822" are equivalent.
The Internet Assigned Numbers Authority (IANA) will maintain a
registry of address-type and mta-name-type values, along with
descriptions of the meanings of each, or a reference to a one or more
specifications that provide such descriptions. (The "rfc822"
address-type is defined in RFC 1891 [8].) Registration forms for
address-type and mta-name-type appear in RFC 1894 [9].
IANA will not accept registrations for any address-type name that
begins with "X-". These type names are reserved for experimental
use.
3.1.3 Lexical tokens imported from RFC 822
The following lexical tokens, defined in RFC 822 [2], are used in the
ABNF grammar for MDNs: atom, CRLF, mailbox, msg-id, text.
3.2 Message/disposition-notification Fields
3.2.1 The Reporting-UA field
reporting-ua-field = "Reporting-UA" ":" ua-name
[ ";" ua-product ]
ua-name = *text
ua-product = *text
The Reporting-UA field is defined as follows:
A MDN describes the disposition of a message after it has been
delivered to a recipient. In all cases, the Reporting-UA is the UA
that performed the disposition described in the MDN. This field is
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optional, but recommended. For Internet Mail user agents, it is
recommended that this field contain both the DNS name of the
particular instance of the UA that generated the MDN and the name of
the product. For example,
Reporting-UA: rogers-mac.dcrt.nih.gov; Foomail 97.1
If the reporting UA consists of more than one component (e.g., a base
program and plug-ins), this may be indicated by including a list of
product names.
3.2.2 The MDN-Gateway field
The MDN-Gateway field indicates the name of the gateway or MTA that
translated a foreign (non-Internet) message disposition notification
into this MDN. This field MUST appear in any MDN which was
translated by a gateway from a foreign system into MDN format, and
MUST NOT appear otherwise.
mdn-gateway-field = "MDN-Gateway" ":" mta-name-type ";" mta-name
mta-name = *text
For gateways into Internet Mail, the MTA-name-type will normally be
"smtp", and the mta-name will be the Internet domain name of the
gateway.
3.2.3 Original-Recipient field
The Original-Recipient field indicates the original recipient address
as specified by the sender of the message for which the MDN is being
issued. For Internet Mail messages the value of the
Original-Recipient field is obtained from the Original-Recipient
header from the message for which the MDN is being generated. If
there is no Original-Recipient header in the message, then the
Original-Recipient field MUST be omitted, unless the same information
is reliably available some other way. If there is an Original-
Recipient header in the original message (or original recipient
information is reliably available some other way), then the
Original-Recipient field must be supplied. If there is more than one
Original-Recipient header in the message, the UA may choose the one
to use or act as if no Original-Recipient header is present.
original-recipient-field =
"Original-Recipient" ":" address-type ";" generic-address
generic-address = *text
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The address-type field indicates the type of the original recipient
address. If the message originated within the Internet, the
address-type field field will normally be "rfc822", and the address
will be according to the syntax specified in RFC 822 [2]. The value
"unknown" should be used if the Reporting UA cannot determine the
type of the original recipient address from the message envelope.
This address is the same as that provided by the sender and can be
used to automatically correlate MDN reports with original messages on
a per recipient basis.
3.2.4 Final-Recipient field
The Final-Recipient field indicates the recipient for which the MDN
is being issued. This field MUST be present.
The syntax of the field is as follows:
final-recipient-field =
"Final-Recipient" ":" address-type ";" generic-address
The generic-address subfield of the Final-Recipient field MUST
contain the mailbox address of the recipient (from the From header of
the MDN) as it was when the MDN was generated by the UA.
The Final-Recipient address may differ from the address originally
provided by the sender, because it may have been transformed during
forwarding and gatewaying into an totally unrecognizable mess.
However, in the absence of the optional Original-Recipient field, the
Final-Recipient field and any returned content may be the only
information available with which to correlate the MDN with a
particular message recipient.
The address-type subfield indicates the type of address expected by
the reporting MTA in that context. Recipient addresses obtained via
SMTP will normally be of address-type "rfc822".
Since mailbox addresses (including those used in the Internet) may be
case sensitive, the case of alphabetic characters in the address MUST
be preserved.
3.2.5 Original-Message-ID field
The Original-Message-ID field indicates the message-ID of the message
for which the MDN is being issued. It is obtained from the Message-
ID header of the message for which the MDN is issued. This field
MUST be present if the original message contained a Message-ID
header. The syntax of the field is
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original-message-id-field = "Original-Message-ID" ":" msg-id
The msg-id token is as specified in RFC 822 [2].
3.2.6 Disposition field
The Disposition field indicates the action performed by the
Reporting-UA on behalf of the user. This field MUST be present.
The syntax for the Disposition field is:
disposition-field = "Disposition" ":" disposition-mode ";"
disposition-type
[ '/' disposition-modifier
*( "," dispostion-modifier ) ]
disposition-mode = action-mode "/" sending-mode
action-mode = "manual-action" / "automatic-action"
sending-mode = "MDN-sent-manually" / "MDN-sent-automatically"
disposition-type = "displayed"
/ "dispatched"
/ "processed"
/ "deleted"
/ "denied"
/ "failed"
disposition-modifier = ( "error" / "warning" )
/ ( "superseded" / "expired" /
"mailbox-terminated" )
/ disposition-modifier-extension
disposition-modifier-extension = atom
The disposition-mode, disposition-type and disposition-modifier may
be spelled in any combination of upper and lower case characters.
3.2.6.1 Disposition modes
The following disposition modes are defined:
"manual-action" The disposition described by the
disposition type was a result of an
explicit instruction by the user rather
than some sort of automatically performed
action.
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"automatic-action" The disposition described by the
disposition type was a result of an
automatic action, rather than an explicit
instruction by the user for this message.
"Manual-action" and "automatic-action" are
mutually exclusive. One or the other must
be specified.
"MDN-sent-manually" The user explicity gave permission for
this particular MDN to be sent.
"MDN-sent-automatically" The MDN was sent because the UA had
previously been configured to do so
automatically.
"MDN-sent-manually" and "MDN-sent-
automatically" are mutually exclusive.
One or the other must be specified.
3.2.6.2 Disposition types
The following disposition-types are defined:
"displayed" The message has been displayed by the UA to someone
reading the recipient's mailbox. There is
no guarantee that the content has been
read or understood.
"dispatched" The message has been sent somewhere in some manner
(e.g., printed, faxed, forwarded) without
necessarily having been previously
displayed to the user. The user may or
may not see the message later.
"processed" The message has been processed in some manner (i.e.,
by some sort of rules or server) without
being displayed to the user. The user may
or may not see the message later, or there
may not even be a human user associated
with the mailbox.
"deleted" The message has been deleted. The recipient may or
may not have seen the message. The
recipient might "undelete" the message at
a later time and read the message.
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"denied" The recipient does not wish the sender to be informed
of the message's disposition. A UA may
also siliently ignore message disposition
requests in this situation.
"failed" A failure occurred that prevented the proper
generation of an MDN. More information
about the cause of the failure may be
contained in a Failure field. The
"failed" disposition type is not to be
used for the situation in which there is
is some problem in processing the message
other than interpreting the request for an
MDN. The "processed" or other disposition
type with appropriate disposition
modifiers is to be used in such
situations.
3.2.6.3 Disposition modifiers
The following disposition modifiers are defined:
"error" An error of some sort occurred
that prevented successful
processing of the message.
Further information is contained
in an Error field.
"warning" The message was successfully
processed but some sort of
exceptional condition occurred.
Further information is contained
in a Warning field.
"superseded" The message has been
automatically rendered obsolete by
another message received. The
recipient may still access and
read the message later.
"expired" The message has reached its
expiration date and has been
automatically removed from the
recipient's mailbox.
"mailbox-terminated" The recipient's mailbox has been
terminated and all message in it
automatically removed.
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"Obsoleted", "expired", and
"terminated" are to be used with
the "deleted" disposition type and
the "autoaction" and "autosent"
disposition modifiers.
disposition-modifier-extension Additional disposition modifiers
may be defined in the future by
later revisions or extensions to
this specification. Disposition
value names beginning with "X-"
will never be defined as standard
values; such names are reserved
for experimental use. MDN
disposition value names NOT
beginning with "X-" MUST be
registered with the Internet
Assigned Numbers Authority (IANA)
and described in a standards-
track RFC or an experimental RFC
approved by the IESG. See Section
10 for a registration form. MDNs
with disposition modifier names
not understood by the receiving UA
MAY be silently ignored or placed
in the user's mailbox without
special inter- pretation. They
MUST not cause any error message
to be sent to the sender of the
MDN.
If an UA developer does not wish
to register the meanings of such
disposition modifier extensions,
"X-" modifiers may be used for
this purpose. To avoid name
collisions, the name of the UA
implementation should follow the
"X-", (e.g. "X-Foomail-fratzed").
It is not required that a UA be able to generate all of the possible
values of the Disposition field.
One and only one MDN may be issued on behalf of each particular
recipient by their user agent. That is, once an MDN has been issued
on behalf of a recipient, no further MDNs may be issued on behalf of
that recipient, even if another disposition is performed on the
message. However, if a message is forwarded, a "dispatched" MDN may
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been issued for the recipient doing the forwarding and the recipient
of the forwarded message may also cause an MDN to be generated.
3.2.7 Failure, Error and Warning fields
The Failure, Error and Warning fields are used to supply additional
information in the form of text messages when the "failure"
disposition type, "error" disposition modifier, and/or the "warning"
disposition modifer appear. The syntax is
failure-field = "Failure" ":" *text
error-field = "Error" ":" *text
warning-field = "Warning" ":" *text
3.3 Extension fields
Additional MDN fields may be defined in the future by later revisions
or extensions to this specification. Extension-field names beginning
with "X-" will never be defined as standard fields; such names are
reserved for experimental use. MDN field names NOT beginning with
"X-" MUST be registered with the Internet Assigned Numbers Authority
(IANA) and described in a standards-track RFC or an experimental RFC
approved by the IESG. See Section 10 for a registration form.
Extension MDN fields may be defined for the following reasons:
(a) To allow additional information from foreign disposition
reports to be tunneled through Internet MDNs. The names of such
MDN fields should begin with an indication of the foreign
environment name (e.g. X400-Physical-Forwarding-Address).
(b) To allow transmission of diagnostic information which is
specific to a particular user agent (UA). The names of such MDN
fields should begin with an indication of the UA implementation
which produced the MDN. (e.g. Foomail-information).
If an application developer does not wish to register the meanings of
such extension fields, "X-" fields may be used for this purpose. To
avoid name collisions, the name of the application implementation
should follow the "X-", (e.g. "X-Foomail-Log-ID" or "X-EDI-info").
4. Timeline of events
The following timeline shows when various events in the processing of
a message and generation of MDNs take place:
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-- User composes message
-- User tells UA to send message
-- UA passes message to MTA (original recipient information
passed along)
-- MTA sends message to next MTA
-- Final MTA receives message
-- Final MTA delivers message to UA (possibily generating DSN)
-- UA performs automatic processing and generates corresponding
MDNs ("dispatched", "processed", "deleted", "denied" or "failed"
disposition type with "automatic-action" and "MDN-sent-
automatically" disposition modes)
-- UA displays list of messages to user
-- User selects a message and requests that some action be
performed on it.
-- UA performs requested action and, with user's permission,
sends appropriate MDN ("displayed", "dispatched", "processed",
"deleted", "denied" or "failed" disposition type with "manual-
action" and "MDN-sent-manually" or "MDN-sent-automatically"
disposition mode).
-- User possibly performs other actions on message, but no
further MDNs are generated.
5. Conformance and Usage Requirements
A UA or gateway conforms to this specification if it generates MDNs
according to the protocol defined in this memo. It is not necessary
to be able to generate all of the possible values of the Disposition
field.
UAs and gateways MUST NOT generate the Original-Recipient field of an
MDN unless the mail protocols provide the address originally
specified by the sender at the time of submission. Ordinary SMTP
does not make that guarantee, but the SMTP extension defined in RFC
1891 [8] permits such information to be carried in the envelope if it
is available. The Original-Recipient header defined in this document
provides a way for the MTA to pass the original recipient address to
the UA.
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Each sender-specified recipient address may result in more than one
MDN. If an MDN is requested for a recipient that is forwarded to
multiple recipients of an "alias" (as defined in RFC 1891 [8],
section 6.2.7.3), each of the recipients may issue an MDN.
Successful distribution of a message to a mailing list exploder
SHOULD be considered final disposition of the message. A mailing
list exploder may issue an MDN with a disposition type of "processed"
and disposition modes of "automatic-action" and "MDN- sent-
automatically" indicating that the message has been forwarded to the
list. In this case, the request for MDNs is not propogated to the
members of the list.
Alternaively, the mailing list exploder may issue no MDN and
propogate the request for MDNs to all members of the list. The
latter behavior is not recommended for any but small, closely knit
lists, as it might cause large numbers of MDNs to be generated and
may cause confidential subscribers to the list to be revealed. It is
also permissible for the mailing list exploder to direct MDNs to
itself, correlate them, and produce a report to the original sender
of the message.
This specification places no restrictions on the processing of MDNs
received by user agents or mailing lists.
6. Security Considerations
The following security considerations apply when using MDNs:
6.1 Forgery
MDNs may be forged as easily as ordinary Internet electronic mail.
User agents and automatic mail handling facilities (such as mail
distribution list exploders) that wish to make automatic use of MDNs
should take appropriate precautions to minimize the potential damage
from denial-of-service attacks.
Security threats related to forged MDNs include the sending of:
(a) A falsified disposition notification when the indicated
disposition of the message has not actually ocurred,
(b) Unsolicited MDNs
6.2 Confidentiality
Another dimension of security is confidentiality. There may be cases
in which a message recipient does not wish the disposition of
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messages addressed to him to be known or is concerned that the
sending of MDNs may reveal other confidential information (e.g., when
the message was read). In this situation, it is acceptable for the
UA to issue "denied" MDNs or to silently ignore requests for MDNs.
If the Disposition-Notification-To header is passed on unmodified
when a message is distributed to the subscribers of a mailing list,
the subscribers to the list may be revealed to the sender of the
original message by the generation of MDNs.
Headers of the original message returned in part 3 of the
multipart/report could reveal confidential information about host
names and/or network topology inside a firewall.
An unencrypted MDN could reveal confidential information about an
encrypted message, especially if all or part of the original message
is returned in part 3 of the multipart/report. Encrypted MDNs are
not defined in this specification.
In general, any optional MDN field may be omitted if the Reporting UA
site or user determines that inclusion of the field would impose too
great a compromise of site confidentiality. The need for such
confidentiality must be balanced against the utility of the omitted
information in MDNs.
6.3 Non-Repudiation
Within the framework of today's Internet Mail, the MDNs defined in
this document provide valuable information to the mail user; however,
MDNs can not be relied upon as a guarantee that a message was or was
not not seen by the recipient. Even if MDNs are not actively forged,
they may be lost in transit. The MDN issuing mechanism may be
bypassed in some manner by the recipient.
7. Collected Grammar
NOTE: The following lexical tokens are defined in RFC 822: atom,
CRLF, mailbox, msg-id, text. The definitions of attribute and value
are as in the definition of the Content-Type header in RFC 2045 [4].
Message headers:
mdn-request-header = "Disposition-Notification-To" ":" 1#mailbox
Disposition-Notification-Options =
"Disposition-Notification-Options" ":"
disposition-notification-parameters
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disposition-notification-parameters = parameter *(";" parameter)
parameter = attribute "=" importance "," 1#value
importance = "required" / "optional"
original-recipient-header =
"Original-Recipient" ":" address-type ";" generic-address
Report content:
disposition-notification-content = [ reporting-ua-field CRLF ]
[ mdn-gateway-field CRLF ]
[ original-recipient-field CRLF ]
final-recipient-field CRLF
[ original-message-id-field CRLF ]
disposition-field CRLF
*( failure-field CRLF )
*( error-field CRLF )
*( warning-field CRLF )
*( extension-field CRLF )
address-type = atom
mta-name-type = atom
reporting-ua-field = "Reporting-UA" ":" ua-name
[ ";" ua-product ]
ua-name = *text
ua-product = *text
mdn-gateway-field = "MDN-Gateway" ":" mta-name-type ";" mta-name
mta-name = *text
original-recipient-field =
"Original-Recipient" ":" address-type ";" generic-address
generic-address = *text
final-recipient-field =
"Final-Recipient" ":" address-type ";" generic-address
disposition-field = "Disposition" ":" disposition-mode ";"
disposition-type
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[ '/' disposition-modifier
*( "," dispostion-modifier ) ]
disposition-mode = action-mode "/" sending-mode
action-mode = "manual-action" / "automatic-action"
sending-mode = "MDN-sent-manually" / "MDN-sent-automatically"
disposition-type = "displayed"
/ "dispatched"
/ "processed"
/ "deleted"
/ "denied"
/ "failed"
disposition-modifier = ( "error" / "warning" )
/ ( "superseded" / "expired" /
"mailbox-terminated" )
/ disposition-modifier-extension
disposition-modifier-extension = atom
original-message-id-field = "Original-Message-ID" ":" msg-id
failure-field = "Failure" ":" *text
error-field = "Error" ":" *text
warning-field = "Warning" ":" *text
extension-field = extension-field-name ":" *text
extension-field-name = atom
8. Guidelines for Gatewaying MDNs
NOTE: This section provides non-binding recommendations for the
construction of mail gateways that wish to provide semi-transparent
disposition notifications between the Internet and another electronic
mail system. Specific MDN gateway requirements for a particular pair
of mail systems may be defined by other documents.
8.1 Gatewaying from other mail systems to MDNs
A mail gateway may issue an MDN to convey the contents of a "foreign"
disposition notification over Internet Mail. When there are
appropriate mappings from the foreign notification elements to MDN
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fields, the information may be transmitted in those MDN fields.
Additional information (such as might be needed to tunnel the foreign
notification through the Internet) may be defined in extension MDN
fields. (Such fields should be given names that identify the foreign
mail protocol, e.g. X400-* for X.400 protocol elements)
The gateway must attempt to supply reasonable values for the
Reporting-UA, Final-Recipient, and Disposition fields. These will
normally be obtained by translating the values from the foreign
notification into their Internet-style equivalents. However, some
loss of information is to be expected.
The sender-specified recipient address, and the original message-id,
if present in the foreign notification, should be preserved in the
Original-Recipient and Original-Message-ID fields.
The gateway should also attempt to preserve the "final" recipient
address from the foreign system. Whenever possible, foreign protocol
elements should be encoded as meaningful printable ASCII strings.
For MDNs produced from foreign disposition notifications, the name of
the gateway MUST appear in the MDN-Gateway field of the MDN.
8.2 Gatewaying from MDNs to other mail systems
It may be possible to gateway MDNs from the Internet into a foreign
mail system. The primary purpose of such gatewaying is to convey
disposition information in a form that is usable by the destination
system. A secondary purpose is to allow "tunneling" of MDNs through
foreign mail systems, in case the MDN may be gatewayed back into the
Internet.
In general, the recipient of the MDN (i.e., the sender of the
original message) will want to know, for each recipient: the closest
available approximation to the original recipient address, and the
disposition (displayed, printed, etc.).
If possible, the gateway should attempt to preserve the Original-
Recipient address and Original-Message-ID (if present), in the
resulting foreign disposition report.
If it is possible to tunnel an MDN through the destination
environment, the gateway specification may define a means of
preserving the MDN information in the disposition reports used by
that environment.
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9. Example
NOTE: This example is provided as illustration only, and is not
considered part of the MDN protocol specification. If the example
conflicts with the protocol definition above, the example is wrong.
Likewise, the use of *-type subfield names or extension fields in
this example is not to be construed as a definition for those type
names or extension fields.
9.1 This is an MDN issued after a message has been displayed to the user
of an Internet Mail user agent.
Date: Wed, 20 Sep 1995 00:19:00 (EDT) -0400
From: Joe Recipient <Joe_Recipient@mega.edu>
Message-Id: <199509200019.12345@mega.edu>
Subject: Disposition notification
To: Jane Sender <Jane_Sender@huge.com>
MIME-Version: 1.0
Content-Type: multipart/report; report-type=disposition-notification;
boundary="RAA14128.773615765/mega.edu"
--RAA14128.773615765/mega.edu
The message sent on 1995 Sep 19 at 13:30:00 (EDT) -0400 to Joe
Recipient <Joe_Recipient@mega.edu> with subject "First draft of
report" has been displayed. This is no guarantee that the message
has been read or understood.
--RAA14128.773615765/mega.edu
content-type: message/disposition-notification
Reporting-UA: joes-pc.cs.mega.edu; Foomail 97.1
Original-Recipient: rfc822;Joe_Recipient@mega.edu
Final-Recipient: rfc822;Joe_Recipient@mega.edu
Original-Message-ID: <199509192301.23456@huge.com>
Disposition: manual-action/MDN-sent-manually; displayed
--RAA14128.773615765/mega.edu
content-type: message/rfc822
[original message goes here]
--RAA14128.773615765/mega.edu--
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10. IANA Registration Forms
The forms below are for use when registering a new parameter name for
the Disposition-Notification-Options header, a new disposition
modifier name, or a new MDN extension field. Each piece of
information required by a registration form may be satisfied either
by providing the information on the form itself, or by including a
reference to a published, publicly available specification that
includes the necessary information. IANA MAY reject registrations
because of incomplete registration forms, imprecise specifications,
or inappropriate names.
To register, complete the applicable form below and send it via
electronic mail to <IANA@IANA.ORG>.
10.1 IANA registration form for Disposition-Notification-Options header
parameter names
A registration for a Disposition-Notification-Options header
parameter name MUST include the following information:
(a) The proposed parameter name.
(b) The syntax for parameter values, specified using BNF, ABNF,
regular expressions, or other non-ambiguous language.
(c) If parameter values are not composed entirely of graphic
characters from the US-ASCII repertoire, a specification for how they
are to be encoded as graphic US-ASCII characters in a Disposition-
Notification-Options header.
(d) A reference to a standards track RFC or experimental RFC approved
by the IESG that describes the semantics of the parameter values.
10.2 IANA registration form for disposition modifer names
A registration for a disposition-modifier name MUST include the
following information:
(a) The proposed disposition-modifier name.
(b) A reference to a standards track RFC or experimental RFC approved
by the IESG that describes the semantics of the disposition modifier.
10.3 IANA registration form for MDN extension field names
A registration for an MDN extension field name MUST include the
following information:
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(a) The proposed extension field name.
(b) The syntax for extension values, specified using BNF, ABNF,
regular expressions, or other non-ambiguous language.
(c) If extension field values are not composed entirely of graphic
characters from the US-ASCII repertoire, a specification for how they
are to be encoded as graphic US-ASCII characters in a Disposition-
Notification-Options header.
(d) A reference to a standards track RFC or experimental RFC approved
by the IESG that describes the semantics of the extension field.
11. Acknowledgments
This document is based on the Delivery Status Notifications document,
RFC 1894 [9], by Keith Moore and Greg Vaudreuil. Contributions were
made by members of the IETF Receipt Working Group, including Harald
Alverstrand, Ian Bell, Urs Eppenberger, Claus Andri Faerber, Ned
Freed, Jim Galvin, Carl Hage, Mike Lake, Keith Moore, Paul Overell,
Pete Resnick, Chuck Shih.
12. References
[1] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
August 1982.
[2] Crocker, D., "Standard for the Format of ARPA Internet Text
Messages", STD 11, RFC 822, August 1982.
[3] Braden, R. (ed.), "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123, October 1989.
[4] Freed, N., and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[5] Freed, N., and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November
1996.
[6] Moore, K., "Multipurpose Internet Mail Extensions (MIME) Part
Three: Message Header Extensions for Non-Ascii Text", RFC
2047, November 1996.
[7] Vaudreuil, G., "The Multipart/Report Content Type for the
Reporting of Mail System Administrative Messages", RFC 1892,
January 1996.
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[8] Moore, K., "SMTP Service Extension for Delivery Status
Notifications", RFC 1891, January 1996.
[9] Moore, K., and G. Vaudreuil, "An Extensible Format for
Delivery Status Notifications, RFC 1894, January 1996.
[10] Bradner, S., "Key Words for Use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
13. Author's Address
Roger Fajman
National Institutes of Health
Building 12A, Room 3063
12 South Drive MSC 5659
Bethesda, Maryland 20892-5659
USA
EMail: raf@cu.nih.gov
Phone: +1 301 402 4265
Fax: +1 301 480 6241
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14. Full Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS 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.
Fajman Standards Track [Page 28]