RFC 2298 - An Extensible Message Format for Message Disposition Notifications

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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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RFC 2298 Message Disposition Notifications March 1998
 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: 1995年9月20日 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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RFC 2298 Message Disposition Notifications March 1998
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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RFC 2298 Message Disposition Notifications March 1998
 (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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RFC 2298 Message Disposition Notifications March 1998
 [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.
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