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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Greg Vaudreuil 3 Internet Draft Octel Network Services 4 Expires: October 20, 1995 April 20, 1995 6 Enhanced Mail System Status Codes 8 10 Status of this Memo 12 This document is an Internet-Draft. Internet-Drafts are working 13 documents of the Internet Engineering Task Force (IETF), its areas, 14 and its working groups. Note that other groups may also distribute 15 working documents as Internet-Drafts. 17 Internet-Drafts are draft documents valid for a maximum of six 18 months and may be updated, replaced, or obsoleted by other documents 19 at any time. It is inappropriate to use Internet- Drafts as 20 reference material or to cite them other than as "work in progress." 22 To learn the current status of any Internet-Draft, please check the 23 "1id-abstracts.txt" listing contained in the Internet- Drafts Shadow 24 Directories on ds.internic.net (US East Coast), nic.nordu.net 25 (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific 26 Rim).Introduction 27 1. Overview 29 There currently is not a standard mechanism for the reporting of 30 mail system errors except for the limited set offered by SMTP and 31 the system specific text descriptions sent in mail messages. There 32 is a pressing need for a rich machine readable status code for use 33 in delivery status notifications [DSN]. This document proposes a 34 new set of status codes for this purpose. 36 SMTP [SMTP] error codes have historically been used for reporting 37 mail system errors. Because of limitations in the SMTP code design, 38 these are not suitable for use in delivery status notifications. 39 SMTP provides about 12 useful codes for delivery reports. The 40 majority of the codes are protocol specific response codes such as 41 the 354 response to the SMTP data command. Each of the 12 useful 42 codes are each overloaded to indicate several error conditions each. 43 SMTP suffers some scars from history, most notably the unfortunate 44 damage to the reply code extension mechanism by uncontrolled use. 45 This proposal facilitates future extensibility by requiring the 46 client to interpret unknown error codes according to the theory of 47 codes while requiring servers to register new response codes. 49 The SMTP theory of reply codes partitioned in the number space such 50 a manner that the remaining available codes will not provide the 51 space needed. The most critical example is the existence of only 5 52 remaining codes for mail system errors. The mail system 53 classification includes both host and mailbox error conditions. The 54 remaining third digit space would be completely consumed as needed 55 to indicate MIME and media conversion errors and security system 56 errors. 58 A revision to the SMTP theory of reply codes to better distribute 59 the error conditions in the number space will necessarily be 60 incompatible with SMTP. Further, consumption of the remaining 61 reply-code number space for delivery notification reporting will 62 reduce the available codes for new ESMTP extensions. 64 The following proposal is based on the SMTP theory of reply codes. 65 It adopts the success, permanent error, and transient error 66 semantics of the first value, with a further description and 67 classification in the second. This proposal re-distributes the 68 classifications to better distribute the error conditions, such as 69 separating mailbox from host errors. 71 2. Status Codes 73 This document defines a new set of status codes to report mail 74 system conditions. These status codes are intended to be used for 75 media and language independent status reporting. They are not 76 intended for system specific diagnostics. 78 The syntax of the new status codes is defined as: 80 status-code = class "." subject "." detail 81 class = "2"/"4"/"5" 82 subject = 1*3digit 83 detail = 1*3digit 85 White-space characters and comments are NOT allowed within a status- 86 code. Each numeric sub-code within the status-code MUST be 87 expressed without leading zero digits. 89 Status codes consist of three numerical fields separated by ".". The 90 first sub-code indicates whether the delivery attempt was 91 successful. The second sub-code indicates the probable source of 92 any delivery anomalies, and the third sub-code indicates a precise 93 error condition. 95 The codes space defined is intended to be extensible only by 96 standards track documents. Mail system specific status codes should 97 be mapped as close as possible to the standard status codes. 98 Servers should send only defined, registered status codes. System 99 specific errors and diagnostics should be carried by means other 100 than status codes. Clients should preserve the extensibility of the 101 code space by reporting the general error described in the subject 102 sub-code when the specific detail is unrecognized. 104 The class sub-code provides a broad classification of the status. 105 The enumerated values the class are defined as: 107 2.X.X Success 109 Success specifies that the DSN is reporting a positive delivery 110 action. Detail sub-codes may provide notification of 111 transformations required for delivery. 113 4.X.X Persistent Transient Failure 115 A persistent transient failure is one in which the message as 116 sent is valid, but some temporary event prevents the successful 117 sending of the message. Sending in the future may be successful. 119 5.X.X Permanent Failure 121 A permanent failure is one which is not likely to be resolved by 122 resending the message in the current form. Some change to the 123 message or the destination must be made for successful delivery. 125 A client must recognize and report class sub-code even where 126 subsequent subject sub-codes are unrecognized. 128 The subject sub-code classifies the status. This value applies to 129 each of the three classifications. The subject sub-code, if 130 recognized, must be reported even if the additional detail provided 131 by the detail sub-code is not recognized. The enumerated values for 132 the subject sub-code are: 134 X.0.X Other or Undefined Status 136 There is no additional subject information available. 138 X.1.X Addressing Status 140 The address status reports on the originator or destination 141 address. It may include address syntax or validity. These 142 errors can generally be corrected by the sender and retried. 144 X.2.X Mailbox Status 146 Mailbox status indicates that something having to do with the 147 mailbox has cause this DSN. Mailbox issues are assumed to be 148 under the general control of the recipient. 150 X.3.X Mail System Status 152 Mail system status indicates that something having to do with the 153 destination system has caused this DSN. System issues are 154 assumed to be under the general control of the destination system 155 administrator. 157 X.4.X Network and Routing Status 159 The networking or routing codes report status about the delivery 160 system itself. These system components include any necessary 161 infrastructure such as directory and routing services. Network 162 issues are assumed to be under the control of the destination or 163 intermediate system administrator. 165 X.5.X Mail Delivery Protocol Status 167 The mail delivery protocol status codes report failures involving 168 the message delivery protocol. These failures include the full 169 range of problems resulting from implementation errors or an 170 unreliable connection. Mail delivery protocol issues may be 171 controlled by many parties including the originating system, 172 destination system, or intermediate system administrators. 174 X.6.X Message Content or Media Status 176 The message content or media status codes report failures 177 involving the content of the message. These codes report 178 failures due to translation, transcoding, or otherwise 179 unsupported message media. Message content or media issues are 180 under the control of both the sender and the receiver, both of 181 whom must support a common set of supported content-types. 183 X.7.X Security or Policy Status 185 The security or policy status codes report failures involving 186 policies such as per-recipient or per-host filtering and 187 cryptographic operations. Security and policy status issues are 188 assumed to be under the control of either or both the sender and 189 recipient. Both the sender and recipient must permit the 190 exchange of messages and arrange the exchange of necessary keys 191 and certificates for cryptographic operations. 193 3. Enumerated Status Codes 195 The following section defines and describes the detail sub-code. The 196 detail value provides more information about the status and is 197 defined relative to the subject of the status. 199 3.1 Other or Undefined Status 201 X.0.0 Other undefined Status 203 Other undefined status is the only undefined error code. It 204 should be used for all errors for which only the class of the 205 error is known. 207 3.2 Address Status 209 X.1.0 Other Address Status 211 Something about the address specified in the message caused this 212 DSN. 214 X.1.1 Bad destination mailbox address 216 The mailbox specified in the address does not exist. For domain 217 names, this means the address portion to the left of the "@" sign 218 is invalid. This code is only useful for permanent failures. 220 X.1.2 Bad destination system address 222 The destination system specified in the address does not exist or 223 is incapable of accepting mail. For domain names, this means the 224 address portion to the right of the "@" is invalid for mail. 225 This codes is only useful for permanent failures. 227 X.1.3 Bad destination mailbox address syntax 229 The destination address was syntactically invalid. This can 230 apply to any field in the address. This code is only useful for 231 permanent failures. 233 X.1.4 Destination mailbox address ambiguous 235 The mailbox address as specified matches one or more recipients 236 on the destination system. This may result if a heuristic 237 address mapping algorithm is used to map the specified address to 238 a local mailbox name. 240 X.1.5 Destination address Valid 242 This mailbox address as specified was valid. This status code 243 should be used for positive delivery reports. 245 X.1.6 Destination mailbox has moved, No forwarding address 247 The mailbox address is was valid but is not longer available 248 resident on the system. This code is only useful for permanent 249 failures. 251 X.1.7 Bad senders mailbox address syntax 253 The senders address was syntactically invalid. This can apply to 254 any field in the address. 256 X.1.8 Bad senders system address 258 The senders system specified in the address does not exist or is 259 incapable of accepting return mail. For domain names, this means 260 the address portion to the right of the "@" is invalid for mail. 262 3.3 Mailbox Status 264 X.2.0 Other or undefined mailbox status 266 The mailbox exists, but something about the destination mailbox 267 has caused the sending of this DSN. 269 X.2.1 Mailbox disabled, not accepting messages 271 The mailbox exists, but is not accepting messages. This may be a 272 permanent error if the mailbox will never be re-enabled or a 273 transient error if the mailbox is only temporarily disabled. 275 X.2.2 Mailbox full 277 The mailbox is full either because the user has exceeded an 278 administrative quota. The general semantics implies that the 279 recipient can delete messages to make more space available. This 280 code should be used as a persistent transient failure. 282 X.2.3 Message length exceeds administrative limit 284 A per-mailbox administrative message length limit has been 285 exceeded. This status code should be used when the per-mailbox 286 message length limit is less than the general system limit. This 287 code should be used as a permanent failure. 289 X.2.4 Mailing list expansion problem 291 The mailbox is a mailing list address and the mailing list was 292 unable to be expanded. This code may represent a permanent 293 failure or a persistent transient failure. 295 3.4 Mail system status 297 X.3.0 Other or undefined mail system status (3.0) 299 The destination system exists and normally accepts mail, but 300 something about the system has caused the generation of this DSN. 302 X.3.1 Mail System full 304 Mail system storage has been exceeded. The general semantics 305 imply that the individual recipient may not be able to delete 306 material to make room for additional messages. This is useful 307 only as a persistent transient error. 309 X.3.2 System not accepting network messages 311 The host on which the mailbox is resident is not accepting 312 messages. Examples of such conditions include an immanent 313 shutdown, excessive load, or system maintenance. This is useful 314 for both permanent and permanent transient errors. 316 X.3.3 System not capable of selected features 318 Selected features specified for the message are not supported by 319 the destination system. This can occur in gateways when features 320 from one domain cannot be mapped onto the supported feature in 321 another. 323 X.3.4 Message too big for system 325 The message is larger than per-message size limit. This limit 326 may either be for physical or administrative reasons. This is 327 useful only as a permanent error. 329 3.5 Network and Routing Status 331 X.4.0 Other or undefined network or routing status 333 Something went wrong with the networking, but it is not clear 334 what the problem is, or the problem cannot be well expressed with 335 any of the other provided detail codes. 337 X.4.1 No answer from host 339 The outbound connection attempt was not answered, either because 340 the remote system was busy, or otherwise unable to take a call. 341 This is useful only as a persistent transient error. 343 X.4.2 Bad connection 345 The outbound connection was established, but was otherwise unable 346 to complete the message transaction, either because of time-out, 347 or inadequate connection quality. This is useful only as a 348 persistent transient error. 350 X.4.3 Directory server failure 352 The network system was unable to forward the message, because a 353 directory server was unavailable. This is useful only as a 354 persistent transient error. 356 The inability to connect to an Internet DNS server is one example 357 of the directory server failure error. 359 X.4.4 Unable to route 361 The mail system was unable to determine the next hop for the 362 message because the necessary routing information was unavailable 363 from the directory server. This is useful for both permanent and 364 persistent transient errors. 366 A DNS lookup returning only an SOA (Start of Administration) 367 record for a domain name is one example of the unable to route 368 error. 370 X.4.5 Mail system congestion 372 The mail system was unable to deliver the message because the 373 mail system was congested. This is useful only as a persistent 374 transient error. 376 X.4.6 Routing loop detected 378 A routing loop caused the message to be forwarded too many times, 379 either because of incorrect routing tables or a user forwarding 380 loop. This is useful only as a persistent transient error. 382 X.4.7 Delivery time expired 384 The message was considered too old by the rejecting system, 385 either because it remained on that host too long or because the 386 time-to-live value specified by the sender of the message was 387 exceeded. This is useful only as a persistent transient error. 389 3.6 Mail Delivery Protocol Status 391 X.5.0 Other or undefined protocol status 393 Something was wrong with the protocol necessary to deliver the 394 message to the next hop and the problem cannot be well expressed 395 with any of the other provided detail codes. 397 X.5.1 Invalid command 399 A mail transaction protocol command was issued which was either 400 out of sequence or unsupported. This is useful only as a 401 permanent error. 403 X.5.2 Syntax error 405 A mail transaction protocol command was issued which could not be 406 interpreted, either because the syntax was wrong or the command 407 is unrecognized. This is useful only as a permanent error. 409 X.5.3 Too many recipients 411 More recipients were specified for the message than could have 412 been delivered by the protocol. This error should normally 413 result in the segmentation of the message into two, the remainder 414 of the recipients to be delivered on a subsequent delivery 415 attempt. It is included in this list in the event that such 416 segmentation is not possible. 418 X.5.4 Invalid command arguments 420 A valid mail transaction protocol command was issued with invalid 421 arguments, either because the arguments were out of range or 422 represented unrecognized features. This is useful only as a 423 permanent error. 425 X.5.5 Wrong protocol version 427 A protocol version mis-match existed which could not be 428 automatically resolved by downgrading one of the communicating 429 parties. This should never happen in ESMTP. 431 3.7 Message Content or Message Media Status 433 X.6.0 Other or undefined media error 435 Something about the content of a message caused it to be 436 considered undeliverable and the problem cannot be well expressed 437 with any of the other provided detail codes. 439 X.6.1 Media not supported 441 The media of the message is not supported by the either the 442 delivery protocol or a host in the forwarding path. This is 443 useful only as a permanent error. 445 X.6.2 Conversion required and prohibited (6.2) 447 The content of the message must be converted before it can be 448 delivered and such conversion is not permitted. Such 449 prohibitions may be the expression of the sender in the message 450 itself or the policy of the sending host. 452 X.6.3 Conversion required but not supported (6.3) 454 The message content must be converted to be forwarded but such 455 conversion is not possible or is not practical by a host in the 456 forwarding path. This condition may result when a relay supports 457 ESMTP transport but not MIME downgrade. 459 X.6.4 Conversion with loss performed 461 This is a warning sent to the sender when message delivery was 462 successfully but when the delivery required a conversion in which 463 some data was lost. 465 X.6.5 Conversion Failed 467 A conversion was required but was unsuccessful. This may be 468 useful as a permanent or persistent temporary notification. 470 3.8 Security or Policy Status 472 X.7.0 Other or undefined security status 474 Something related to security caused the message to be returned, 475 and the problem cannot be well expressed with any of the other 476 provided detail codes. This status code may also be used when 477 the condition cannot be further described because of security 478 policies in force. 480 X.7.1 Delivery not authorized, message refused 482 The sender is not authorized to send to the destination. This 483 can be the result of per-host or per-recipient filtering. This 484 memo does not discuss the merits of any such filtering, but 485 provides a mechanism to report such. This is useful only as a 486 permanent error. 488 X.7.2 Mailing list expansion prohibited 490 The sender is not authorized to send a message to the intended 491 mailing list. This is useful only as a permanent error. 493 X.7.3 Security conversion required but not possible 495 A conversion from one secure messaging protocol to another was 496 required for delivery and such conversion was not possible. This 497 is useful only as a permanent error. 499 X.7.4 Security features not supported 501 A message contained security features such as secure 502 authentication which could not be supported on the delivery 503 protocol. This is useful only as a permanent error. 505 X.7.5 Cryptographic failure 507 A transport system otherwise authorized to validate or decrypt a 508 message in transport was unable to do so because necessary 509 information such as key was not available or such information was 510 invalid. This is useful only as a permanent error. 512 X.7.6 Cryptographic algorithm not supported 514 A transport system otherwise authorized to validate or decrypt a 515 message was unable to do so because the necessary algorithm was 516 not supported. 518 X.7.7 Message integrity failure 520 A transport system otherwise authorized to validate a message was 521 unable to do so because the message was corrupted or altered. 522 This may be useful as a permanent, transient persistent, or 523 successful delivery code. 525 4. References 527 [SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821, 528 USC/Information Sciences Institute, August 1982. 530 [DSN] Moore, K., Vaudreuil, G., "An Extensible Message Format for 531 Delivery Status Notifications", Internet-Draft. 533 5. Security Consideration 535 This document describes a status code system with increased 536 precision. Use of these status codes may disclose additional 537 information about how an internal mail system is implemented beyond 538 that currently available. 540 6. Acknowledgments 542 The author wishes to offer special thank Harald Alvestrand, Marko 543 Kaittola, and Keith Moore for their extensive review and 544 constructive suggestions. 546 7. Author's Address 548 Gregory M. Vaudreuil 549 Octel Network Services 550 17060 Dallas Parkway 551 Suite 214 552 Dallas, TX 75248-1905 553 Voice/Fax: +1-214-733-2722 554 Greg.Vaudreuil@Octel.com 556 8. Appendix - Collected Status Codes 558 X.1.0 Other Address Status 559 X.1.1 Bad destination mailbox address 560 X.1.2 Bad destination system address 561 X.1.3 Bad destination mailbox address syntax 562 X.1.4 Destination mailbox address ambiguous 563 X.1.5 Destination mailbox address valid 564 X.1.6 Mailbox has moved 565 X.1.7 Bad senders mailbox address syntax 566 X.1.8 Bad senders system address 568 X.2.0 Other or undefined mailbox status 569 X.2.1 Mailbox disabled, not accepting messages 570 X.2.2 Mailbox full 571 X.2.3 Message length exceeds administrative limit. 572 X.2.4 Mailing list expansion problem 574 X.3.0 Other or undefined mail system status 575 X.3.1 Mail system full 576 X.3.2 System not accepting network messages 577 X.3.3 System not capable of selected features 578 X.3.4 Message too big for system 580 X.4.0 Other or undefined network or routing status 581 X.4.1 No answer from host 582 X.4.2 Bad connection 583 X.4.3 Routing server failure 584 X.4.4 Unable to route 585 X.4.5 Network congestion 586 X.4.6 Routing loop detected 587 X.4.7 Delivery time expired 589 X.5.0 Other or undefined protocol status 590 X.5.1 Invalid command 591 X.5.2 Syntax error 592 X.5.3 Too many recipients 593 X.5.4 Invalid command arguments 594 X.5.5 Wrong protocol version 596 X.6.0 Other or undefined media error 597 X.6.1 Media not supported 598 X.6.2 Conversion required and prohibited 599 X.6.3 Conversion required but not supported 600 X.6.4 Conversion with loss performed 601 X.6.5 Conversion failed 602 X.7.0 Other or undefined security status 603 X.7.1 Delivery not authorized, message refused 604 X.7.2 Mailing list expansion prohibited 605 X.7.3 Security conversion required but not possible 606 X.7.4 Security features not supported 607 X.7.5 Cryptographic failure 608 X.7.6 Cryptographic algorithm not supported 609 X.7.7 Message integrity failure