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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.
Fajman Standards Track [Page 1]
RFC 2298 Message Disposition Notifications March 1998 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; Fajman Standards Track [Page 2]
RFC 2298 Message Disposition Notifications March 1998 (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 Fajman Standards Track [Page 3]
RFC 2298 Message Disposition Notifications March 1998 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. Fajman Standards Track [Page 4]
RFC 2298 Message Disposition Notifications March 1998 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]. Fajman Standards Track [Page 5]
RFC 2298 Message Disposition Notifications March 1998 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 Fajman Standards Track [Page 6]
RFC 2298 Message Disposition Notifications March 1998 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. Fajman Standards Track [Page 7]
RFC 2298 Message Disposition Notifications March 1998 (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 Fajman Standards Track [Page 8]
RFC 2298 Message Disposition Notifications March 1998 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: Fajman Standards Track [Page 9]
RFC 2298 Message Disposition Notifications March 1998 (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 Fajman Standards Track [Page 10]
RFC 2298 Message Disposition Notifications March 1998 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 Fajman Standards Track [Page 11]
RFC 2298 Message Disposition Notifications March 1998 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 Fajman Standards Track [Page 12]
RFC 2298 Message Disposition Notifications March 1998 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. Fajman Standards Track [Page 13]
RFC 2298 Message Disposition Notifications March 1998 "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. Fajman Standards Track [Page 14]
RFC 2298 Message Disposition Notifications March 1998 "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. Fajman Standards Track [Page 15]
RFC 2298 Message Disposition Notifications March 1998 "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 Fajman Standards Track [Page 16]
RFC 2298 Message Disposition Notifications March 1998 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: Fajman Standards Track [Page 17]
RFC 2298 Message Disposition Notifications March 1998 -- 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. Fajman Standards Track [Page 18]
RFC 2298 Message Disposition Notifications March 1998 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 Fajman Standards Track [Page 19]
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 Fajman Standards Track [Page 20]
RFC 2298 Message Disposition Notifications March 1998 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 Fajman Standards Track [Page 21]
RFC 2298 Message Disposition Notifications March 1998 [ '/' 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 Fajman Standards Track [Page 22]
RFC 2298 Message Disposition Notifications March 1998 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. Fajman Standards Track [Page 23]
RFC 2298 Message Disposition Notifications March 1998 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-- Fajman Standards Track [Page 24]
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: Fajman Standards Track [Page 25]
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. Fajman Standards Track [Page 26]
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 Fajman Standards Track [Page 27]
RFC 2298 Message Disposition Notifications March 1998 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]