Network Working Group K. Moore Request for Comments: 1894 University of Tennessee Category: Standards Track G. Vaudreuil Octel Network Services January 1996
Because many messages are sent between the Internet and other messaging systems (such as X.400 or the so-called "LAN-based" systems), the DSN 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 and error codes, in addition to those normally used in Internet mail. Additional attributes may also be defined to support "tunneling" of foreign notifications through Internet mail.
Any questions, comments, and reports of defects or ambiguities in this specification may be sent to the mailing list for the NOTARY working group of the IETF, using the address firstname.lastname@example.org. Requests to subscribe to the mailing list should be addressed to email@example.com. Implementors of this specification are encouraged to subscribe to the mailing list, so that they will quickly be informed of any problems which might hinder interoperability.
NOTE: This document is a Proposed Standard. If and when this protocol is submitted for Draft Standard status, any normative text (phrases containing SHOULD, SHOULD NOT, MUST, MUST NOT, or MAY) in this document will be re-evaluated in light of implementation experience, and are thus subject to change.
This memo defines only the format of the notifications. An extension to the Simple Message Transfer Protocol (SMTP) [RFC 821] to fully support such notifications is the subject of a separate memo [RFC 1891].
Several DSN fields are defined in terms of the view from a particular MTA in the transmission. The MTAs are assigned the following names:
If the delivery attempts described occurred in a "foreign" (non- Internet) mail system, and the DSN was produced by translating the foreign notice into DSN format, the Reporting MTA will still identify the "foreign" MTA where the delivery attempts occurred.
Figure 1 illustrates the relationship between the various MTAs.
+-----+ +--------+ +---------+ +---------+ +------+ | | | | |Received-| | | | | | | => |Original| => ... => | From | => |Reporting| ===> |Remote| | user| | MTA | | MTA | | MTA | <No! | MTA | |agent| +--------+ +---------+ +----v----+ +------+ | | | | | <-------------------------------------------+ +-----+ (DSN returned to sender by Reporting MTA) Figure 1. Original, Received-From, Reporting and Remote MTAsEach of these MTAs may provide information which is useful in a DSN:
Similarly, the DSN might contain an "envelope identifier" that was known to both the sender's user agent and the Original MTA at the time of message submission, and which, if included in the DSN, can be used by the sender to keep track of which messages were or were not delivered.
Extension fields may also be added by the Reporting MTA as needed to provide additional information for use in a trouble ticket or to preserve information for tunneling of foreign delivery reports through Internet DSNs.
The Original, Reporting, and Remote MTAs may exist in very different environments and use dissimilar transport protocols, MTA names, address formats, and delivery status codes. DSNs therefore do not assume any particular format for mailbox addresses, MTA names, or transport-specific status codes. Instead, the various DSN fields that carry such quantities consist of a "type" subfield followed by a subfield whose contents are ordinary text characters, and the format of which is indicated by the "type" subfield. This allows a DSN to convey these quantities regardless of format.
The DSN MUST be addressed (in both the message header and the transport envelope) to the return address from the transport envelope which accompanied the original message for which the DSN was generated. (For a message that arrived via SMTP, the envelope return address appears in the MAIL FROM command.)
The From field of the message header of the DSN SHOULD contain the address of a human who is responsible for maintaining the mail system at the Reporting MTA site (e.g. Postmaster), so that a reply to the DSN will reach that person. Exception: if a DSN is translated from a foreign delivery report, and the gateway performing the translation cannot determine the appropriate address, the From field of the DSN MAY be the address of a human who is responsible for maintaining the gateway.
The envelope sender address of the DSN SHOULD be chosen to ensure that no delivery status reports will be issued in response to the DSN itself, and MUST be chosen so that DSNs will not generate mail loops. Whenever an SMTP transaction is used to send a DSN, the MAIL FROM command MUST use a NULL return address, i.e. "MAIL FROM:<>".
A particular DSN describes the delivery status for exactly one message. However, an MTA MAY report on the delivery status for several recipients of the same message in a single DSN. Due to the nature of the mail transport system (where responsibility for delivery of a message to its recipients may be split among several MTAs, and delivery to any particular recipient may be delayed), multiple DSNs may be still be issued in response to a single message submission.
MIME type name: message MIME subtype name: delivery-status 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 4 of this memo.The message/delivery-status report type for use in the multipart/report is "delivery-status".
The body of a message/delivery-status consists of one or more "fields" formatted according to the ABNF of RFC 822 header "fields" (see RFC 822). The per-message fields appear first, followed by a blank line. Following the per-message fields are one or more groups of per-recipient fields. Each group of per-recipient fields is preceded by a blank line. Using the ABNF of RFC 822, the syntax of the message/delivery-status content is as follows:
delivery-status-content = per-message-fields 1*( CRLF per-recipient-fields )The per-message fields are described in section 2.2. The per- recipient fields are described in section 2.3.
A number of DSN fields are defined to have a portion of a field body of "xtext". "xtext" is used to allow encoding sequences of octets which contain values outside the range [1-127 decimal] of traditional ASCII characters, and also to allow comments to be inserted in the data. Any octet may be encoded as "+" followed by two upper case hexadecimal digits. (The "+" character MUST be encoded as "+2B".) With certain exceptions, octets that correspond to ASCII characters may be represented as themselves. SPACE and HTAB characters are ignored. Comments may be included by enclosing them in parenthesis. Except within comments, encoded-words such as defined in RFC 1522 may NOT be used in xtext.
"xtext" is formally defined as follows:
xtext = *( xchar / hexchar / linear-white-space / comment ) xchar = any ASCII CHAR between "!" (33) and "~" (126) inclusive, except for "+", "\" and "("."hexchar"s are intended to encode octets that cannot be represented as plain text, either because they are reserved, or because they are non-printable. However, any octet value may be represented by a "hexchar".
hexchar = ASCII "+" immediately followed by two upper case hexadecimal digitsWhen encoding an octet sequence as xtext:
The "-type" subfields are defined as follows:
address-type = atom
diagnostic-type = atom
mta-name-type = atom
The Internet Assigned Numbers Authority (IANA) will maintain a registry of address-types, diagnostic-types, and MTA-name-types, along with descriptions of the meanings and acceptable values of each, or a reference to a one or more specifications that provide such descriptions. (The "rfc822" address-type, "smtp" diagnostic- type, and "dns" MTA-name-type are defined in RFC 1891.) Registration forms for address-type, diagnostic-type, and MTA-name-type appear in section 8 of this document.
IANA will not accept registrations for any address-type, diagnostic- type, or MTA-name-type name that begins with "X-". These type names are reserved for experimental use.
per-message-fields = [ original-envelope-id-field CRLF ] reporting-mta-field CRLF [ dsn-gateway-field CRLF ] [ received-from-mta-field CRLF ] [ arrival-date-field CRLF ] *( extension-field CRLF )
If such an envelope identifier was present in the envelope which accompanied the message when it arrived at the Reporting MTA, it SHOULD be supplied in the Original-Envelope-Id field of any DSNs issued as a result of an attempt to deliver the message. Except when a DSN is issued by the sender's MTA, an MTA MUST NOT supply this field unless there is an envelope-identifier field in the envelope which accompanied this message on its arrival at the Reporting MTA.
The Original-Envelope-Id field is defined as follows:
original-envelope-id-field = "Original-Envelope-Id" ":" envelope-id envelope-id = *textThere may be at most one Original-Envelope-Id field per DSN.
The envelope-id is CASE-SENSITIVE. The DSN MUST preserve the original case and spelling of the envelope-id.
NOTE: The Original-Envelope-Id is NOT the same as the Message-Id from the message header. The Message-Id identifies the content of the message, while the Original-Envelope-Id identifies the transaction in which the message is sent.
reporting-mta-field = "Reporting-MTA" ":" mta-name-type ";" mta-name mta-name = *textThe Reporting-MTA field is defined as follows:
A DSN describes the results of attempts to deliver, relay, or gateway a message to one or more recipients. In all cases, the Reporting-MTA is the MTA which attempted to perform the delivery, relay, or gateway operation described in the DSN. This field is required.
Note that if an SMTP client attempts to relay a message to an SMTP server and receives an error reply to a RCPT command, the client is responsible for generating the DSN, and the client's domain name will appear in the Reporting-MTA field. (The server's domain name will appear in the Remote-MTA field.)
Note that the Reporting-MTA is not necessarily the MTA which actually issued the DSN. For example, if an attempt to deliver a message outside of the Internet resulted in a nondelivery notification which was gatewayed back into Internet mail, the Reporting-MTA field of the resulting DSN would be that of the MTA that originally reported the delivery failure, not that of the gateway which converted the foreign notification into a DSN. See Figure 2.
sender's environment recipient's environment ............................ .......................................... : : (1) : : (2) +-----+ +--------+ +--------+ +---------+ +---------+ +------+ | | | | | | |Received-| | | | | | |=>|Original|=>| |->| From |->|Reporting|-->|Remote| | user| | MTA | | | | MTA | | MTA |<No| MTA | |agent| +--------+ |Gateway | +---------+ +----v----+ +------+ | | | | | | | <============| |<-------------------+ +-----+ | |(4) (3) +--------+ : : ...........................: :.........................................Figure 2. DSNs in the presence of gateways
Because the exact spelling of an MTA name may be significant in a particular environment, MTA names are CASE-SENSITIVE.
dsn-gateway-field = "DSN-Gateway" ":" mta-name-type ";" mta-nameFor 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.
received-from-mta-field = "Received-From-MTA" ":" mta-name-type ";" mta-nameIf the message was received from an Internet host via SMTP, the contents of the mta-name subfield SHOULD be the Internet domain name supplied in the HELO or EHLO command, and the network address used by the SMTP client SHOULD be included as a comment enclosed in parentheses. (In this case, the MTA-name-type will be "smtp".)
The mta-name portion of the Received-From-MTA field is formatted according to the conventions indicated by the MTA-name-type subfield.
Since case is significant in some mail systems, the exact spelling, including case, of the MTA name SHOULD be preserved.
arrival-date-field = "Arrival-Date" ":" date-timeThe date and time are expressed in RFC 822 'date-time' format, as modified by RFC 1123. Numeric timezones ([+/-]HHMM format) MUST be used.
The syntax for the group of per-recipient fields is as follows:
per-recipient-fields = [ original-recipient-field CRLF ] final-recipient-field CRLF action-field CRLF status-field CRLF [ remote-mta-field CRLF ] [ diagnostic-code-field CRLF ] [ last-attempt-date-field CRLF ] [ will-retry-until-field CRLF ] *( extension-field CRLF )
original-recipient-field = "Original-Recipient" ":" address-type ";" generic-address generic-address = *textThe 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. The value "unknown" should be used if the Reporting MTA cannot determine the type of the original recipient address from the message envelope.
This field is optional. It should be included only if the sender- specified recipient address was present in the message envelope, such as by the SMTP extensions defined in RFC 1891. This address is the same as that provided by the sender and can be used to automatically correlate DSN reports and message transactions.
The syntax of the field is as follows:
final-recipient-field = "Final-Recipient" ":" address-type ";" generic-addressThe generic-address subfield of the Final-Recipient field MUST contain the mailbox address of the recipient (from the transport envelope) as it was when the message was accepted for delivery by the Reporting MTA.
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 DSN with a particular message submission.
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".
NOTE: The Reporting MTA is not expected to ensure that the address actually conforms to the syntax conventions of the address-type. Instead, it MUST report exactly the address received in the envelope, unless that address contains characters such as CR or LF which may not appear in a DSN field.
Since mailbox addresses (including those used in the Internet) may be case sensitive, the case of alphabetic characters in the address MUST be preserved.
The syntax for the action-field is:
action-field = "Action" ":" action-value action-value = "failed" / "delayed" / "delivered" / "relayed" / "expanded"The action-value may be spelled in any combination of upper and lower case characters.
Using the terms "mailing list" and "alias" as defined in
NOTE ON ACTION VS. STATUS CODES: Although the 'action' field might seem to be redundant with the 'status' field, this is not the case. In particular, a "temporary failure" ("4") status code could be used with an action-value of either "delayed" or "failed". For example, assume that an SMTP client repeatedly tries to relay a message to the mail exchanger for a recipient, but fails because a query to a domain name server timed out. After a few hours, it might issue a "delayed" DSN to inform the sender that the message had not yet been delivered. After a few days, the MTA might abandon its attempt to deliver the message and return a "failed" DSN. The status code (which would begin with a "4" to indicate "temporary failure") would be the same for both DSNs.
Another example for which the action and status codes may appear contradictory: If an MTA or mail gateway cannot deliver a message because doing so would entail conversions resulting in an unacceptable loss of information, it would issue a DSN with the 'action' field of "failure" and a status code of 'XXX'. If the message had instead been relayed, but with some loss of information, it might generate a DSN with the same XXX status-code, but with an action field of "relayed".
The syntax of the status field is:
status-field = "Status" ":" status-code status-code = DIGIT "." 1*3DIGIT "." 1*3DIGIT ; White-space characters and comments are NOT allowed within a ; status-code, though a comment enclosed in parentheses MAY follow ; the last numeric subfield of the status-code. Each numeric ; subfield within the status-code MUST be expressed without ; leading zero digits.Status codes thus consist of three numerical fields separated by ".". The first sub-field indicates whether the delivery attempt was successful (2 = success, 4 = persistent temporary failure, 5 = permanent failure). The second sub-field indicates the probable source of any delivery anomalies, and the third sub-field denotes a precise error condition, if known.
The initial set of status-codes is defined in RFC 1893 .
remote-mta-field = "Remote-MTA" ":" mta-name-type ";" mta-nameNOTE: The Remote-MTA field preserves the "while talking to" information that was provided in some pre-existing nondelivery reports.
This field is optional. It MUST NOT be included if no remote MTA was involved in the attempted delivery of the message to that recipient.
diagnostic-code-field = "Diagnostic-Code" ":" diagnostic-type ";" *textNOTE: The information in the Diagnostic-Code field may be somewhat redundant with that from the Status field. The Status field is needed so that any DSN, regardless of origin, may be understood by any user agent or gateway that parses DSNs. Since the Status code will sometimes be less precise than the actual transport diagnostic code, the Diagnostic-Code field is provided to retain the latter information. Such information may be useful in a trouble ticket sent to the administrator of the Reporting MTA, or when tunneling foreign nondelivery reports through DSNs.
If the Diagnostic Code was obtained from a Remote MTA during an attempt to relay the message to that MTA, the Remote-MTA field should be present. When interpreting a DSN, the presence of a Remote-MTA field indicates that the Diagnostic Code was issued by the Remote MTA. The absence of a Remote-MTA indicates that the Diagnostic Code was issued by the Reporting MTA.
In addition to the Diagnostic-Code itself, additional textual description of the diagnostic, MAY appear in a comment enclosed in parentheses.
This field is optional, because some mail systems supply no additional information beyond that which is returned in the 'action' and 'status' fields. However, this field SHOULD be included if transport-specific diagnostic information is available.
last-attempt-date-field = "Last-Attempt-Date" ":" date-timeThis field is optional. It MUST NOT be included if the actual date and time of the last delivery attempt are not available (which might be the case if the DSN were being issued by a gateway).
The date and time are expressed in RFC 822 'date-time' format, as modified by RFC 1123. Numeric timezones ([+/-]HHMM format) MUST be used.
final-log-id-field = "Final-Log-ID" ":" *textThis field is optional.
will-retry-until-field = "Will-Retry-Until" ":" date-timeThe date and time are expressed in RFC 822. 'date-time' format, as modified by RFC 1123. Numeric timezones ([+/-]HHMM format) MUST be used.
Extension DSN fields may be defined for the following reasons:
If an MTA 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 MTA implementation should follow the "X-", (e.g. "X-Foomail-Log-ID").
A minimal implementation of this specification need generate only the Reporting-MTA per-message field, and the Final-Recipient, Action, and Status fields for each attempt to deliver a message to a recipient described by the DSN. Generation of the other fields, when appropriate, is strongly recommended.
MTAs and gateways MUST NOT generate the Original-Recipient field of a DSN unless the mail transfer protocol provides 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 permits such information to be carried in the envelope if it is available.)
Each sender-specified recipient address SHOULD result in at most one "delivered" or "failed" DSN for that recipient. If a positive DSN is requested (e.g. one using NOTIFY=SUCCESS in SMTP) for a recipient that is forwarded to multiple recipients of an "alias" (as defined in RFC 1891 , section 7.2.7), the forwarding MTA SHOULD normally issue a "expanded" DSN for the originally-specified recipient and not propagate the request for a DSN to the forwarding addresses. Alternatively, the forwarding MTA MAY relay the request for a DSN to exactly one of the forwarding addresses and not propagate the request to the others.
By contrast, successful submission of a message to a mailing list exploder is considered final delivery of the message. Upon delivery of a message to a recipient address corresponding to a mailing list exploder, the Reporting MTA SHOULD issue an appropriate DSN exactly as if the recipient address were that of an ordinary mailbox.
NOTE: This is actually intended to make DSNs usable by mailing lists themselves. Any message sent to a mailing list subscriber should have its envelope return address pointing to the list maintainer [see RFC 1123, section 5.3.7(E)]. Since DSNs are sent to the envelope return address, all DSNs resulting from delivery to the recipients of a mailing list will be sent to the list maintainer. The list maintainer may elect to mechanically process DSNs upon receipt, and thus automatically delete invalid addresses from the list. (See section 7 of this memo.)
This specification places no restrictions on the processing of DSNs received by user agents or distribution lists.
Security threats related to forged DSNs include the sending of:
MTA authors are encouraged to provide a mechanism which enables the end user to preserve the confidentiality of a forwarding address. Depending on the degree of confidentiality required, and the nature of the environment to which a message were being forwarded, this might be accomplished by one or more of:
Implementors are cautioned that many existing MTAs will send nondelivery notifications to a return address in the message header (rather than to the one in the envelope), in violation of SMTP and other protocols. If a message is forwarded through such an MTA, no reasonable action on the part of the forwarding MTA will prevent the downstream MTA from compromising the forwarding address. Likewise, if the recipient's MTA automatically responds to messages based on a request in the message header (such as the nonstandard, but widely used, Return-Receipt-To extension header), it will also compromise the forwarding address.
For example, a race condition in the SMTP protocol allows for the duplication of messages if the connection is dropped following a completed DATA command, but before a response is seen by the SMTP client. This will cause the SMTP client to retransmit the message, even though the SMTP server has already accepted it. [RFC 1047] If one of those delivery attempts succeeds and the other one fails, a "failed" DSN could be issued even though the message actually reached the recipient.
action-field = "Action" ":" action-value action-value = "failed" / "delayed" / "delivered" / "relayed" / "expanded" address-type = atom arrival-date-field = "Arrival-Date" ":" date-time delivery-status-content = per-message-fields 1*( CRLF per-recipient-fields ) diagnostic-code-field = "Diagnostic-Code" ":" diagnostic-type ";" *text diagnostic-type = atom dsn-gateway-field = "DSN-Gateway" ":" mta-name-type ";" mta-name envelope-id = *text extension-field = extension-field-name ":" *text extension-field-name = atom final-recipient-field = "Final-Recipient" ":" address-type ";" generic-address generic-address = *text last-attempt-date-field = "Last-Attempt-Date" ":" date-time mta-name = *text mta-name-type = atom original-envelope-id-field = "Original-Envelope-Id" ":" envelope-id original-recipient-field = "Original-Recipient" ":" address-type ";" generic-address per-message-fields = [ original-envelope-id-field CRLF ] reporting-mta-field CRLF [ dsn-gateway-field CRLF ] [ received-from-mta-field CRLF ] [ arrival-date-field CRLF ] *( extension-field CRLF ) per-recipient-fields = [ original-recipient-field CRLF ] final-recipient-field CRLF action-field CRLF status-field CRLF [ remote-mta-field CRLF ] [ diagnostic-code-field CRLF ] [ last-attempt-date-field CRLF ] [ will-retry-until-field CRLF ] *( extension-field CRLF ) received-from-mta-field = "Received-From-MTA" ":" mta-name-type ";" mta-name remote-mta-field = "Remote-MTA" ":" mta-name-type ";" mta-name reporting-mta-field = "Reporting-MTA" ":" mta-name-type ";" mta-name status-code = DIGIT "." 1*3DIGIT "." 1*3DIGIT ; White-space characters and comments are NOT allowed within a ; status-code, though a comment enclosed in parentheses MAY follow ; the last numeric subfield of the status-code. Each numeric ; subfield within the status-code MUST be expressed without ; leading zero digits. status-field = "Status" ":" status-code will-retry-until-field = "Will-Retry-Until" ":" date-time
The gateway must attempt to supply reasonable values for the Reporting-MTA, Final-Recipient, Action, and Status fields. These will normally be obtained by translating the values from the remote delivery or non-delivery notification into their Internet-style equivalents. However, some loss of information is to be expected. For example, the set of status-codes defined for DSNs may not be adequate to fully convey the delivery diagnostic code from the foreign system. The gateway should assign the most precise code which describes the failure condition, falling back on "generic" codes such as 2.0.0 (success), 4.0.0 (temporary failure), and 5.0.0 (permanent failure) when necessary. The actual foreign diagnostic code should be retained in the Diagnostic-Code field (with an appropriate diagnostic-type value) for use in trouble tickets or tunneling.
The sender-specified recipient address, and the original envelope-id, if present in the foreign transport envelope, should be preserved in the Original-Recipient and Original-Envelope-ID fields.
The gateway should also attempt to preserve the "final" recipient addresses and MTA names from the foreign system. Whenever possible, foreign protocol elements should be encoded as meaningful printable ASCII strings.
For DSNs produced from foreign delivery or nondelivery notifications, the name of the gateway MUST appear in the DSN-Gateway field of the DSN.
In general, the recipient of the DSN (i.e., the sender of the original message) will want to know, for each recipient: the closest available approximation to the original recipient address, the delivery status (success, failure, or temporary failure), and for failed deliveries, a diagnostic code that describes the reason for the failure.
If possible, the gateway should attempt to preserve the Original- Recipient address and Original-Envelope-ID (if present), in the resulting foreign delivery status report.
When reporting delivery failures, if the diagnostic-type subfield of the Diagnostic-Code field indicates that the original diagnostic code is understood by the destination environment, the information from the Diagnostic-Code field should be used. Failing that, the information in the Status field should be mapped into the closest available diagnostic code used in the destination environment.
If it is possible to tunnel a DSN through the destination environment, the gateway specification may define a means of preserving the DSN information in the delivery status reports used by that environment.
DSNs are designed to be used by mailing list exploders to allow them to detect and automatically delete recipients for whom mail delivery fails repeatedly.
When forwarding a message to list subscribers, the mailing list exploder should always set the envelope return address (e.g. SMTP MAIL FROM address) to point to a special address which is set up to received nondelivery reports. A "smart" mailing list exploder can therefore intercept such nondelivery reports, and if they are in the DSN format, automatically examine them to determine for which recipients a message delivery failed or was delayed.
The Original-Recipient field should be used if available, since it should exactly match the subscriber address known to the list. If the Original-Recipient field is not available, the recipient field may resemble the list subscriber address. Often, however, the list subscriber will have forwarded his mail to a different address, or the address may be subject to some re-writing, so heuristics may be required to successfully match an address from the recipient field. Care is needed in this case to minimize the possibility of false matches.
The reason for delivery failure can be obtained from the Status and Action fields, and from the Diagnostic-Code field (if the status-type is recognized). Reports for recipients with action values other than "failed" can generally be ignored; in particular, subscribers should not be removed from a list due to "delayed" reports.
In general, almost any failure status code (even a "permanent" one) can result from a temporary condition. It is therefore recommended that a list exploder not delete a subscriber based on any single failure DSN (regardless of the status code), but only on the persistence of delivery failure over a period of time.
However, some kinds of failures are less likely than others to have been caused by temporary conditions, and some kinds of failures are more likely to be noticed and corrected quickly than others. Once more precise status codes are defined, it may be useful to differentiate between the status codes when deciding whether to delete a subscriber. For example, on a list with a high message volume, it might be desirable to temporarily suspend delivery to a recipient address which causes repeated "temporary" failures, rather than simply deleting the recipient. The duration of the suspension might depend on the type of error. On the other hand, a "user unknown" error which persisted for several days could be considered a reliable indication that address were no longer valid.
To register a DSN type, complete the applicable form below and send
it via Internet electronic mail to
Likewise, the use of *-type subfield names or extension fields in
these examples is not to be construed as a definition for those type
names or extension fields.
These examples were manually translated from bounced messages using
whatever information was available.
Gregory M. Vaudreuil An Extensible Message Format for Delivery Status Notifications
Changes by Uwe Ohse:
The proposed address-type name.
The syntax for mailbox addresses of this type, specified using BNF, regular expressions, ASN.1, or other non-ambiguous language.
If addresses of this type 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 DSN Original-Recipient or Final-Recipient DSN field.
[optional] A specification for how addresses of this type are to be translated to and from Internet electronic mail addresses.
8.2 IANA registration form for diagnostic-type
A registration for a DSN address-type MUST include the following
9. Appendix - Examples
NOTE: These examples are provided as illustration only, and are not
considered part of the DSN protocol specification. If an example
conflicts with the protocol definition above, the example is wrong.
This is a simple DSN issued after repeated attempts
to deliver a message failed. In this case, the DSN is
issued by the same MTA from which the message was originated.
Date: Thu, 7 Jul 1994 17:16:05 -0400
From: Mail Delivery Subsystem <MAILER-DAEMON@CS.UTK.EDU>
Subject: Returned mail: Cannot send message for 5 days
Content-Type: multipart/report; report-type=delivery-status;
The original message was received at Sat, 2 Jul 1994 17:10:28 -0400
----- The following addresses had delivery problems -----
<firstname.lastname@example.org> (unrecoverable error)
----- Transcript of session follows -----
<email@example.com>... Deferred: Connection timed out
Message could not be delivered for 5 days
Message will be deleted from queue
Reporting-MTA: dns; cs.utk.edu
Diagnostic-Code: smtp; 426 connection timed out
Last-Attempt-Date: Thu, 7 Jul 1994 17:15:49 -0400
[original message goes here]
This is another DSN issued by the sender's MTA, which
contains details of multiple delivery attempts. Some of
these were detected locally, and others by a remote MTA.
Date: Fri, 8 Jul 1994 09:21:47 -0400
From: Mail Delivery Subsystem <MAILER-DAEMON@CS.UTK.EDU>
Subject: Returned mail: User unknown
Content-Type: multipart/report; report-type=delivery-status;
content-type: text/plain; charset=us-ascii
----- The following addresses had delivery problems -----
<firstname.lastname@example.org> (unrecoverable error)
<email@example.com> (unrecoverable error)
Reporting-MTA: dns; cs.utk.edu
Status: 5.0.0 (permanent failure)
550 'arathib@vnet.IBM.COM' is not a registered gateway user
Remote-MTA: dns; vnet.ibm.com
Status: 4.0.0 (hpnjld.njd.jp.com: host name lookup failure)
Diagnostic-Code: smtp; 550 user unknown
Remote-MTA: dns; sdcc13.ucsd.edu
[original message goes here]
A delivery report generated by Message Router (MAILBUS) and
gatewayed by PMDF_MR to a DSN. In this case the gateway did not
have sufficient information to supply an original-recipient address.
Date: Fri, 08 Jul 1994 09:21:25 -0400 (EDT)
From: Message Router Submission Agent <AMMGR@corp.timeplex.com>
Subject: Status of : Re: Battery current sense
content-type: multipart/report; report-type=delivery-status;
Invalid address - nair_s
%DIR-E-NODIRMTCH, No matching Directory Entry found
Reporting-MTA: mailbus; SYS30
Final-Recipient: unknown; nair_s
Status: 5.0.0 (unknown permanent failure)
A delay report from a multiprotocol MTA. Note that there is no
returned content, so no third body part appears in the DSN.
Received: from nsfnet-relay.ac.uk by sun2.nsfnet-relay.ac.uk
Sun, 10 Jul 1994 00:36:51 +0100
Date: Sun, 10 Jul 1994 00:36:51 +0100
Subject: WARNING: message delayed at "nsfnet-relay.ac.uk"
content-type: multipart/report; report-type=delivery-status;
The following message:
UA-ID: Reliable PC (...
has not been delivered to the intended recipient:
despite repeated delivery attempts over the past 24 hours.
The usual cause of this problem is that the remote system is
Delivery will continue to be attempted up to a total elapsed
time of 168 hours, ie 7 days.
You will be informed if delivery proves to be impossible
within this time.
Please quote the Q-ID in any queries regarding this mail.
Reporting-MTA: dns; sun2.nsfnet-relay.ac.uk
Status: 4.0.0 (unknown temporary failure)
The authors wish to thank the following people for their reviews of
earlier drafts of this document and their suggestions for
improvement: Eric Allman, Harald Alvestrand, Allan Cargille, Jim
Conklin, Peter Cowen, Dave Crocker, Roger Fajman, Ned Freed, Marko
Kaittola, Steve Kille, John Klensin, John Gardiner Myers, Mark
Nahabedian, Julian Onions, Jacob Palme, Jean Charles Roy, and Gregory
Borenstein, N., Freed, N. "Multipurpose Internet Mail Extensions", RFC 1521 Bellcore, Innosoft, September 1993.
Vaudreuil, G., "The Multipart/Report Content Type for the Reporting of Mail System Administrative Messages", RFC 1892 , Octal Network Services, January 1996.
Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821, USC/Information Sciences Institute, August 1982.
Moore, K., "SMTP Service Extension for Delivery Status Notifications", RFC 1891, University of Tennessee, January 1996.
Vaudreuil, G., "Enhanced Mail System Status Codes", RFC 1893 , Octal Network Services, January 1996.
Crocker, D., "Standard for the Format of ARPA Internet Text Messages", STD 11, RFC 822, UDEL, August 1982.
Moore, K. "MIME (Multipurpose Internet Mail Extensions) Part Two: Message Header Extensions for Non-Ascii Text", RFC 1522 , University of Tennessee, September 1993.
Braden, R. (ed.) "Requirements for Internet Hosts - Application and Support", STD 3, RFC 1123 , USC/Information Sciences Institute, October 1989.
Partridge, C., "Duplicate Messages and SMTP", RFC 1047, BBN, February 1988.
12. Authors' Addresses
University of Tennessee
107 Ayres Hall
Knoxville, TN 37996-1301
Phone: +1 615 974 3126
Fax: +1 615 974 8296
Octel Network Services
17080 Dallas Parkway
Dallas, TX 75248-1905
Likewise, the use of *-type subfield names or extension fields in these examples is not to be construed as a definition for those type names or extension fields.
These examples were manually translated from bounced messages using whatever information was available.
Gregory M. Vaudreuil
An Extensible Message Format for Delivery Status Notifications
HTML-Version: Uwe Ohse (20.10.1996)
Changes by Uwe Ohse: