7Network Working Group G. Vaudreuil
8Request for Comments: 3463 Lucent Technologies
9Obsoletes: 1893 January 2003
10Category: Standards Track
13 Enhanced Mail System Status Codes
17 This document specifies an Internet standards track protocol for the
18 Internet community, and requests discussion and suggestions for
19 improvements. Please refer to the current edition of the "Internet
20 Official Protocol Standards" (STD 1) for the standardization state
21 and status of this protocol. Distribution of this memo is unlimited.
25 Copyright (C) The Internet Society (2003). All Rights Reserved.
29 This document defines a set of extended status codes for use within
30 the mail system for delivery status reports, tracking, and improved
31 diagnostics. In combination with other information provided in the
32 Delivery Status Notification (DSN) delivery report, these codes
33 facilitate media and language independent rendering of message
38 1. Overview ......................................................2
39 2. Status Code Structure .........................................3
40 3. Enumerated Status Codes .......................................5
41 3.1 Other or Undefined Status ...................................6
42 3.2 Address Status ..............................................6
43 3.3 Mailbox Status ..............................................7
44 3.4 Mail system status ..........................................8
45 3.5 Network and Routing Status ..................................9
46 3.6 Mail Delivery Protocol Status ..............................10
47 3.7 Message Content or Message Media Status ....................11
48 3.8 Security or Policy Status ..................................12
49 4. References ...................................................13
50 5. Security Considerations ......................................13
51 Appendix A - Collected Status Codes ..........................14
52 Appendix B - Changes from RFC1893 ............................15
53 Author's Address .............................................15
54 Full Copyright Statement .....................................16
58Vaudreuil Standards Track [Page 1]
60RFC 3463 Enhanced Mail System Status Codes January 2003
65 There is a need for a standard mechanism for the reporting of mail
66 system errors richer than the limited set offered by SMTP and the
67 system specific text descriptions sent in mail messages. There is a
68 pressing need for a rich machine-readable, human language independent
69 status code for use in delivery status notifications [DSN]. This
70 document proposes a new set of status codes for this purpose.
72 SMTP [SMTP] error codes have historically been used for reporting
73 mail system errors. Because of limitations in the SMTP code design,
74 these are not suitable for use in delivery status notifications.
75 SMTP provides about 12 useful codes for delivery reports. The
76 majority of the codes are protocol specific response codes such as
77 the 354 response to the SMTP data command. Each of the 12 useful
78 codes are overloaded to indicate several error conditions. SMTP
79 suffers some scars from history, most notably the unfortunate damage
80 to the reply code extension mechanism by uncontrolled use. This
81 proposal facilitates future extensibility by requiring the client to
82 interpret unknown error codes according to the theory of codes while
83 requiring servers to register new response codes.
85 The SMTP theory of reply codes are partitioned in the number space in
86 such a manner that the remaining available codes will not provide the
87 space needed. The most critical example is the existence of only 5
88 remaining codes for mail system errors. The mail system
89 classification includes both host and mailbox error conditions. The
90 remaining third digit space would be completely consumed as needed to
91 indicate MIME and media conversion errors and security system errors.
93 A revision to the SMTP theory of reply codes to better distribute the
94 error conditions in the number space will necessarily be incompatible
95 with SMTP. Further, consumption of the remaining reply-code number
96 space for delivery notification reporting will reduce the available
97 codes for new ESMTP extensions.
99 The following status code set is based on the SMTP theory of reply
100 codes. It adopts the success, permanent error, and transient error
101 semantics of the first value, with a further description and
102 classification in the second. This proposal re-distributes the
103 classifications to better distribute the error conditions, such as
104 separating mailbox from host errors.
108 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
109 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
110 document are to be interpreted as described in BCP 14 [RFC2119].
114Vaudreuil Standards Track [Page 2]
116RFC 3463 Enhanced Mail System Status Codes January 2003
1192. Status Code Structure
121 This document defines a new set of status codes to report mail system
122 conditions. These status codes are used for media and language
123 independent status reporting. They are not intended for system
124 specific diagnostics.
126 The syntax of the new status codes is defined as:
128 status-code = class "." subject "." detail
136 White-space characters and comments are NOT allowed within a status-
137 code. Each numeric sub-code within the status-code MUST be expressed
138 without leading zero digits.
140 Status codes consist of three numerical fields separated by ".". The
141 first sub-code indicates whether the delivery attempt was successful.
142 The second sub-code indicates the probable source of any delivery
143 anomalies, and the third sub-code indicates a precise error
148 The code space defined is intended to be extensible only by standards
149 track documents. Mail system specific status codes should be mapped
150 as close as possible to the standard status codes. Servers should
151 send only defined, registered status codes. System specific errors
152 and diagnostics should be carried by means other than status codes.
154 New subject and detail codes will be added over time. Because the
155 number space is large, it is not intended that published status codes
156 will ever be redefined or eliminated. Clients should preserve the
157 extensibility of the code space by reporting the general error
158 described in the subject sub-code when the specific detail is
170Vaudreuil Standards Track [Page 3]
172RFC 3463 Enhanced Mail System Status Codes January 2003
175 The class sub-code provides a broad classification of the status.
176 The enumerated values for each class are defined as:
180 Success specifies that the DSN is reporting a positive delivery
181 action. Detail sub-codes may provide notification of
182 transformations required for delivery.
184 4.XXX.XXX Persistent Transient Failure
186 A persistent transient failure is one in which the message as
187 sent is valid, but persistence of some temporary condition has
188 caused abandonment or delay of attempts to send the message.
189 If this code accompanies a delivery failure report, sending in
190 the future may be successful.
192 5.XXX.XXX Permanent Failure
194 A permanent failure is one which is not likely to be resolved
195 by resending the message in the current form. Some change to
196 the message or the destination must be made for successful
199 A client must recognize and report class sub-code even where
200 subsequent subject sub-codes are unrecognized.
202 The subject sub-code classifies the status. This value applies to
203 each of the three classifications. The subject sub-code, if
204 recognized, must be reported even if the additional detail provided
205 by the detail sub-code is not recognized. The enumerated values for
206 the subject sub-code are:
208 X.0.XXX Other or Undefined Status
210 There is no additional subject information available.
212 X.1.XXX Addressing Status
214 The address status reports on the originator or destination
215 address. It may include address syntax or validity. These
216 errors can generally be corrected by the sender and retried.
218 X.2.XXX Mailbox Status
220 Mailbox status indicates that something having to do with the
221 mailbox has caused this DSN. Mailbox issues are assumed to be
222 under the general control of the recipient.
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228RFC 3463 Enhanced Mail System Status Codes January 2003
231 X.3.XXX Mail System Status
233 Mail system status indicates that something having to do with
234 the destination system has caused this DSN. System issues are
235 assumed to be under the general control of the destination
236 system administrator.
238 X.4.XXX Network and Routing Status
240 The networking or routing codes report status about the
241 delivery system itself. These system components include any
242 necessary infrastructure such as directory and routing
243 services. Network issues are assumed to be under the control
244 of the destination or intermediate system administrator.
246 X.5.XXX Mail Delivery Protocol Status
248 The mail delivery protocol status codes report failures
249 involving the message delivery protocol. These failures
250 include the full range of problems resulting from
251 implementation errors or an unreliable connection.
253 X.6.XXX Message Content or Media Status
255 The message content or media status codes report failures
256 involving the content of the message. These codes report
257 failures due to translation, transcoding, or otherwise
258 unsupported message media. Message content or media issues are
259 under the control of both the sender and the receiver, both of
260 which must support a common set of supported content-types.
262 X.7.XXX Security or Policy Status
264 The security or policy status codes report failures involving
265 policies such as per-recipient or per-host filtering and
266 cryptographic operations. Security and policy status issues
267 are assumed to be under the control of either or both the
268 sender and recipient. Both the sender and recipient must
269 permit the exchange of messages and arrange the exchange of
270 necessary keys and certificates for cryptographic operations.
2723. Enumerated Status Codes
274 The following section defines and describes the detail sub-code. The
275 detail value provides more information about the status and is
276 defined relative to the subject of the status.
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284RFC 3463 Enhanced Mail System Status Codes January 2003
289 X.0.0 Other undefined Status
291 Other undefined status is the only undefined error code. It
292 should be used for all errors for which only the class of the
297 X.1.0 Other address status
299 Something about the address specified in the message caused
302 X.1.1 Bad destination mailbox address
304 The mailbox specified in the address does not exist. For
305 Internet mail names, this means the address portion to the left
306 of the "@" sign is invalid. This code is only useful for
309 X.1.2 Bad destination system address
311 The destination system specified in the address does not exist
312 or is incapable of accepting mail. For Internet mail names,
313 this means the address portion to the right of the "@" is
314 invalid for mail. This code is only useful for permanent
317 X.1.3 Bad destination mailbox address syntax
319 The destination address was syntactically invalid. This can
320 apply to any field in the address. This code is only useful
321 for permanent failures.
323 X.1.4 Destination mailbox address ambiguous
325 The mailbox address as specified matches one or more recipients
326 on the destination system. This may result if a heuristic
327 address mapping algorithm is used to map the specified address
328 to a local mailbox name.
330 X.1.5 Destination address valid
332 This mailbox address as specified was valid. This status code
333 should be used for positive delivery reports.
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340RFC 3463 Enhanced Mail System Status Codes January 2003
343 X.1.6 Destination mailbox has moved, No forwarding address
345 The mailbox address provided was at one time valid, but mail is
346 no longer being accepted for that address. This code is only
347 useful for permanent failures.
349 X.1.7 Bad sender's mailbox address syntax
351 The sender's address was syntactically invalid. This can apply
352 to any field in the address.
354 X.1.8 Bad sender's system address
356 The sender's system specified in the address does not exist or
357 is incapable of accepting return mail. For domain names, this
358 means the address portion to the right of the "@" is invalid
363 X.2.0 Other or undefined mailbox status
365 The mailbox exists, but something about the destination mailbox
366 has caused the sending of this DSN.
368 X.2.1 Mailbox disabled, not accepting messages
370 The mailbox exists, but is not accepting messages. This may be
371 a permanent error if the mailbox will never be re-enabled or a
372 transient error if the mailbox is only temporarily disabled.
376 The mailbox is full because the user has exceeded a per-mailbox
377 administrative quota or physical capacity. The general
378 semantics implies that the recipient can delete messages to
379 make more space available. This code should be used as a
380 persistent transient failure.
384 A per-mailbox administrative message length limit has been
385 exceeded. This status code should be used when the per-mailbox
386 message length limit is less than the general system limit.
387 This code should be used as a permanent failure.
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396RFC 3463 Enhanced Mail System Status Codes January 2003
399 X.2.4 Mailing list expansion problem
401 The mailbox is a mailing list address and the mailing list was
402 unable to be expanded. This code may represent a permanent
403 failure or a persistent transient failure.
407 X.3.0 Other or undefined mail system status
409 The destination system exists and normally accepts mail, but
410 something about the system has caused the generation of this
413 X.3.1 Mail system full
415 Mail system storage has been exceeded. The general semantics
416 imply that the individual recipient may not be able to delete
417 material to make room for additional messages. This is useful
418 only as a persistent transient error.
422 The host on which the mailbox is resident is not accepting
423 messages. Examples of such conditions include an immanent
424 shutdown, excessive load, or system maintenance. This is
425 useful for both permanent and persistent transient errors.
427 X.3.3 System not capable of selected features
429 Selected features specified for the message are not supported
430 by the destination system. This can occur in gateways when
431 features from one domain cannot be mapped onto the supported
434 X.3.4 Message too big for system
436 The message is larger than per-message size limit. This limit
437 may either be for physical or administrative reasons. This is
438 useful only as a permanent error.
440 X.3.5 System incorrectly configured
442 The system is not configured in a manner that will permit it to
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452RFC 3463 Enhanced Mail System Status Codes January 2003
457 X.4.0 Other or undefined network or routing status
459 Something went wrong with the networking, but it is not clear
460 what the problem is, or the problem cannot be well expressed
461 with any of the other provided detail codes.
463 X.4.1 No answer from host
465 The outbound connection attempt was not answered, because
466 either the remote system was busy, or was unable to take a
467 call. This is useful only as a persistent transient error.
471 The outbound connection was established, but was unable to
472 complete the message transaction, either because of time-out,
473 or inadequate connection quality. This is useful only as a
474 persistent transient error.
476 X.4.3 Directory server failure
478 The network system was unable to forward the message, because a
479 directory server was unavailable. This is useful only as a
480 persistent transient error.
482 The inability to connect to an Internet DNS server is one
483 example of the directory server failure error.
485 X.4.4 Unable to route
487 The mail system was unable to determine the next hop for the
488 message because the necessary routing information was
489 unavailable from the directory server. This is useful for both
490 permanent and persistent transient errors.
492 A DNS lookup returning only an SOA (Start of Administration)
493 record for a domain name is one example of the unable to route
496 X.4.5 Mail system congestion
498 The mail system was unable to deliver the message because the
499 mail system was congested. This is useful only as a persistent
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508RFC 3463 Enhanced Mail System Status Codes January 2003
511 X.4.6 Routing loop detected
513 A routing loop caused the message to be forwarded too many
514 times, either because of incorrect routing tables or a user-
515 forwarding loop. This is useful only as a persistent transient
518 X.4.7 Delivery time expired
520 The message was considered too old by the rejecting system,
521 either because it remained on that host too long or because the
522 time-to-live value specified by the sender of the message was
523 exceeded. If possible, the code for the actual problem found
524 when delivery was attempted should be returned rather than this
529 X.5.0 Other or undefined protocol status
531 Something was wrong with the protocol necessary to deliver the
532 message to the next hop and the problem cannot be well
533 expressed with any of the other provided detail codes.
535 X.5.1 Invalid command
537 A mail transaction protocol command was issued which was either
538 out of sequence or unsupported. This is useful only as a
543 A mail transaction protocol command was issued which could not
544 be interpreted, either because the syntax was wrong or the
545 command is unrecognized. This is useful only as a permanent
548 X.5.3 Too many recipients
550 More recipients were specified for the message than could have
551 been delivered by the protocol. This error should normally
552 result in the segmentation of the message into two, the
553 remainder of the recipients to be delivered on a subsequent
554 delivery attempt. It is included in this list in the event
555 that such segmentation is not possible.
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564RFC 3463 Enhanced Mail System Status Codes January 2003
567 X.5.4 Invalid command arguments
569 A valid mail transaction protocol command was issued with
570 invalid arguments, either because the arguments were out of
571 range or represented unrecognized features. This is useful
572 only as a permanent error.
574 X.5.5 Wrong protocol version
576 A protocol version mis-match existed which could not be
577 automatically resolved by the communicating parties.
581 X.6.0 Other or undefined media error
583 Something about the content of a message caused it to be
584 considered undeliverable and the problem cannot be well
585 expressed with any of the other provided detail codes.
587 X.6.1 Media not supported
589 The media of the message is not supported by either the
590 delivery protocol or the next system in the forwarding path.
591 This is useful only as a permanent error.
593 X.6.2 Conversion required and prohibited
595 The content of the message must be converted before it can be
596 delivered and such conversion is not permitted. Such
597 prohibitions may be the expression of the sender in the message
598 itself or the policy of the sending host.
600 X.6.3 Conversion required but not supported
602 The message content must be converted in order to be forwarded
603 but such conversion is not possible or is not practical by a
604 host in the forwarding path. This condition may result when an
605 ESMTP gateway supports 8bit transport but is not able to
606 downgrade the message to 7 bit as required for the next hop.
608 X.6.4 Conversion with loss performed
610 This is a warning sent to the sender when message delivery was
611 successfully but when the delivery required a conversion in
612 which some data was lost. This may also be a permanent error
613 if the sender has indicated that conversion with loss is
614 prohibited for the message.
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620RFC 3463 Enhanced Mail System Status Codes January 2003
623 X.6.5 Conversion Failed
625 A conversion was required but was unsuccessful. This may be
626 useful as a permanent or persistent temporary notification.
630 X.7.0 Other or undefined security status
632 Something related to security caused the message to be
633 returned, and the problem cannot be well expressed with any of
634 the other provided detail codes. This status code may also be
635 used when the condition cannot be further described because of
636 security policies in force.
638 X.7.1 Delivery not authorized, message refused
640 The sender is not authorized to send to the destination. This
641 can be the result of per-host or per-recipient filtering. This
642 memo does not discuss the merits of any such filtering, but
643 provides a mechanism to report such. This is useful only as a
646 X.7.2 Mailing list expansion prohibited
648 The sender is not authorized to send a message to the intended
649 mailing list. This is useful only as a permanent error.
651 X.7.3 Security conversion required but not possible
653 A conversion from one secure messaging protocol to another was
654 required for delivery and such conversion was not possible.
655 This is useful only as a permanent error.
657 X.7.4 Security features not supported
659 A message contained security features such as secure
660 authentication that could not be supported on the delivery
661 protocol. This is useful only as a permanent error.
663 X.7.5 Cryptographic failure
665 A transport system otherwise authorized to validate or decrypt
666 a message in transport was unable to do so because necessary
667 information such as key was not available or such information
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676RFC 3463 Enhanced Mail System Status Codes January 2003
679 X.7.6 Cryptographic algorithm not supported
681 A transport system otherwise authorized to validate or decrypt
682 a message was unable to do so because the necessary algorithm
685 X.7.7 Message integrity failure
687 A transport system otherwise authorized to validate a message
688 was unable to do so because the message was corrupted or
689 altered. This may be useful as a permanent, transient
690 persistent, or successful delivery code.
6924. Normative References
694 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
695 Requirement Levels", BCP 14, RFC 2119, March 1997.
697 [SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC
700 [DSN] Moore, K. and G. Vaudreuil, "An Extensible Message Format
701 for Delivery Status Notifications", RFC 3464, January 2003.
7035. Security Considerations
705 This document describes a status code system with increased
706 precision. Use of these status codes may disclose additional
707 information about how an internal mail system is implemented beyond
708 that currently available.
730Vaudreuil Standards Track [Page 13]
732RFC 3463 Enhanced Mail System Status Codes January 2003
735Appendix A - Collected Status Codes
737 X.1.0 Other address status
738 X.1.1 Bad destination mailbox address
739 X.1.2 Bad destination system address
740 X.1.3 Bad destination mailbox address syntax
741 X.1.4 Destination mailbox address ambiguous
742 X.1.5 Destination mailbox address valid
743 X.1.6 Mailbox has moved
744 X.1.7 Bad sender's mailbox address syntax
745 X.1.8 Bad sender's system address
747 X.2.0 Other or undefined mailbox status
748 X.2.1 Mailbox disabled, not accepting messages
750 X.2.3 Message length exceeds administrative limit.
751 X.2.4 Mailing list expansion problem
753 X.3.0 Other or undefined mail system status
754 X.3.1 Mail system full
755 X.3.2 System not accepting network messages
756 X.3.3 System not capable of selected features
757 X.3.4 Message too big for system
759 X.4.0 Other or undefined network or routing status
760 X.4.1 No answer from host
762 X.4.3 Routing server failure
763 X.4.4 Unable to route
764 X.4.5 Network congestion
765 X.4.6 Routing loop detected
766 X.4.7 Delivery time expired
768 X.5.0 Other or undefined protocol status
769 X.5.1 Invalid command
771 X.5.3 Too many recipients
772 X.5.4 Invalid command arguments
773 X.5.5 Wrong protocol version
775 X.6.0 Other or undefined media error
776 X.6.1 Media not supported
777 X.6.2 Conversion required and prohibited
778 X.6.3 Conversion required but not supported
779 X.6.4 Conversion with loss performed
780 X.6.5 Conversion failed
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788RFC 3463 Enhanced Mail System Status Codes January 2003
791 X.7.0 Other or undefined security status
792 X.7.1 Delivery not authorized, message refused
793 X.7.2 Mailing list expansion prohibited
794 X.7.3 Security conversion required but not possible
795 X.7.4 Security features not supported
796 X.7.5 Cryptographic failure
797 X.7.6 Cryptographic algorithm not supported
798 X.7.7 Message integrity failure
800Appendix B - Changes from RFC1893
802 Changed Authors contact information.
804 Updated required standards boilerplate.
806 Edited the text to make it spell-checker and grammar checker
809 Modified the text describing the persistent transient failure to more
810 closely reflect current practice and understanding.
812 Eliminated the restriction on the X.4.7 codes limiting them to
813 persistent transient errors.
822 Phone: +1 214 823 9325
823 EMail: GregV@ieee.org
842Vaudreuil Standards Track [Page 15]
844RFC 3463 Enhanced Mail System Status Codes January 2003
847Full Copyright Statement
849 Copyright (C) The Internet Society (2003). All Rights Reserved.
851 This document and translations of it may be copied and furnished to
852 others, and derivative works that comment on or otherwise explain it
853 or assist in its implementation may be prepared, copied, published
854 and distributed, in whole or in part, without restriction of any
855 kind, provided that the above copyright notice and this paragraph are
856 included on all such copies and derivative works. However, this
857 document itself may not be modified in any way, such as by removing
858 the copyright notice or references to the Internet Society or other
859 Internet organizations, except as needed for the purpose of
860 developing Internet standards in which case the procedures for
861 copyrights defined in the Internet Standards process must be
862 followed, or as required to translate it into languages other than
865 The limited permissions granted above are perpetual and will not be
866 revoked by the Internet Society or its successors or assigns.
868 This document and the information contained herein is provided on an
869 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
870 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
871 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
872 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
873 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
877 Funding for the RFC Editor function is currently provided by the
898Vaudreuil Standards Track [Page 16]