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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: 11/5/1995 May 5, 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). 28 1. Overview 30 There currently is not a standard mechanism for the reporting of 31 mail system errors except for the limited set offered by SMTP and 32 the system specific text descriptions sent in mail messages. There 33 is a pressing need for a rich machine readable status code for use 34 in delivery status notifications [DSN]. This document proposes a 35 new set of status codes for this purpose. 37 SMTP [SMTP] error codes have historically been used for reporting 38 mail system errors. Because of limitations in the SMTP code design, 39 these are not suitable for use in delivery status notifications. 40 SMTP provides about 12 useful codes for delivery reports. The 41 majority of the codes are protocol specific response codes such as 42 the 354 response to the SMTP data command. Each of the 12 useful 43 codes are each overloaded to indicate several error conditions each. 44 SMTP suffers some scars from history, most notably the unfortunate 45 damage to the reply code extension mechanism by uncontrolled use. 46 This proposal facilitates future extensibility by requiring the 47 client to interpret unknown error codes according to the theory of 48 codes while requiring servers to register new response codes. 50 The SMTP theory of reply codes partitioned in the number space such 51 a manner that the remaining available codes will not provide the 52 space needed. The most critical example is the existence of only 5 53 remaining codes for mail system errors. The mail system 54 classification includes both host and mailbox error conditions. The 55 remaining third digit space would be completely consumed as needed 56 to indicate MIME and media conversion errors and security system 57 errors. 59 A revision to the SMTP theory of reply codes to better distribute 60 the error conditions in the number space will necessarily be 61 incompatible with SMTP. Further, consumption of the remaining 62 reply-code number space for delivery notification reporting will 63 reduce the available codes for new ESMTP extensions. 65 The following proposal is based on the SMTP theory of reply codes. 66 It adopts the success, permanent error, and transient error 67 semantics of the first value, with a further description and 68 classification in the second. This proposal re-distributes the 69 classifications to better distribute the error conditions, such as 70 separating mailbox from host errors. 72 2. Status Codes 74 This document defines a new set of status codes to report mail 75 system conditions. These status codes are intended to be used for 76 media and language independent status reporting. They are not 77 intended for system specific diagnostics. 79 The syntax of the new status codes is defined as: 81 status-code = class "." subject "." detail 82 class = "2"/"4"/"5" 83 subject = 1*3digit 84 detail = 1*3digit 86 White-space characters and comments are NOT allowed within a status- 87 code. Each numeric sub-code within the status-code MUST be 88 expressed without leading zero digits. 90 Status codes consist of three numerical fields separated by ".". The 91 first sub-code indicates whether the delivery attempt was 92 successful. The second sub-code indicates the probable source of 93 any delivery anomalies, and the third sub-code indicates a precise 94 error condition. 96 The codes space defined is intended to be extensible only by 97 standards track documents. Mail system specific status codes should 98 be mapped as close as possible to the standard status codes. 99 Servers should send only defined, registered status codes. System 100 specific errors and diagnostics should be carried by means other 101 than status codes. 103 New subject and detail codes will be added over time. Because the 104 number space is large, it is not intended that published status 105 codes will ever be redefined or eliminated. Clients should preserve 106 the extensibility of the code space by reporting the general error 107 described in the subject sub-code when the specific detail is 108 unrecognized. 110 The class sub-code provides a broad classification of the status. 111 The enumerated values the class are defined as: 113 2.X.X Success 115 Success specifies that the DSN is reporting a positive delivery 116 action. Detail sub-codes may provide notification of 117 transformations required for delivery. 119 4.X.X Persistent Transient Failure 121 A persistent transient failure is one in which the message as 122 sent is valid, but some temporary event prevents the successful 123 sending of the message. Sending in the future may be successful. 125 5.X.X Permanent Failure 126 A permanent failure is one which is not likely to be resolved by 127 resending the message in the current form. Some change to the 128 message or the destination must be made for successful delivery. 130 A client must recognize and report class sub-code even where 131 subsequent subject sub-codes are unrecognized. 133 The subject sub-code classifies the status. This value applies to 134 each of the three classifications. The subject sub-code, if 135 recognized, must be reported even if the additional detail provided 136 by the detail sub-code is not recognized. The enumerated values for 137 the subject sub-code are: 139 X.0.X Other or Undefined Status 141 There is no additional subject information available. 143 X.1.X Addressing Status 145 The address status reports on the originator or destination 146 address. It may include address syntax or validity. These 147 errors can generally be corrected by the sender and retried. 149 X.2.X Mailbox Status 151 Mailbox status indicates that something having to do with the 152 mailbox has cause this DSN. Mailbox issues are assumed to be 153 under the general control of the recipient. 155 X.3.X Mail System Status 157 Mail system status indicates that something having to do with the 158 destination system has caused this DSN. System issues are 159 assumed to be under the general control of the destination system 160 administrator. 162 X.4.X Network and Routing Status 164 The networking or routing codes report status about the delivery 165 system itself. These system components include any necessary 166 infrastructure such as directory and routing services. Network 167 issues are assumed to be under the control of the destination or 168 intermediate system administrator. 170 X.5.X Mail Delivery Protocol Status 172 The mail delivery protocol status codes report failures involving 173 the message delivery protocol. These failures include the full 174 range of problems resulting from implementation errors or an 175 unreliable connection. Mail delivery protocol issues may be 176 controlled by many parties including the originating system, 177 destination system, or intermediate system administrators. 179 X.6.X Message Content or Media Status 181 The message content or media status codes report failures 182 involving the content of the message. These codes report 183 failures due to translation, transcoding, or otherwise 184 unsupported message media. Message content or media issues are 185 under the control of both the sender and the receiver, both of 186 whom must support a common set of supported content-types. 188 X.7.X Security or Policy Status 190 The security or policy status codes report failures involving 191 policies such as per-recipient or per-host filtering and 192 cryptographic operations. Security and policy status issues are 193 assumed to be under the control of either or both the sender and 194 recipient. Both the sender and recipient must permit the 195 exchange of messages and arrange the exchange of necessary keys 196 and certificates for cryptographic operations. 198 3. Enumerated Status Codes 200 The following section defines and describes the detail sub-code. The 201 detail value provides more information about the status and is 202 defined relative to the subject of the status. 204 3.1 Other or Undefined Status 206 X.0.0 Other undefined Status 208 Other undefined status is the only undefined error code. It 209 should be used for all errors for which only the class of the 210 error is known. 212 3.2 Address Status 214 X.1.0 Other address status 216 Something about the address specified in the message caused this 217 DSN. 219 X.1.1 Bad destination mailbox address 221 The mailbox specified in the address does not exist. For domain 222 names, this means the address portion to the left of the "@" sign 223 is invalid. This code is only useful for permanent failures. 225 X.1.2 Bad destination system address 227 The destination system specified in the address does not exist or 228 is incapable of accepting mail. For domain names, this means the 229 address portion to the right of the "@" is invalid for mail. 230 This codes is only useful for permanent failures. 232 X.1.3 Bad destination mailbox address syntax 234 The destination address was syntactically invalid. This can 235 apply to any field in the address. This code is only useful for 236 permanent failures. 238 X.1.4 Destination mailbox address ambiguous 240 The mailbox address as specified matches one or more recipients 241 on the destination system. This may result if a heuristic 242 address mapping algorithm is used to map the specified address to 243 a local mailbox name. 245 X.1.5 Destination address valid 247 This mailbox address as specified was valid. This status code 248 should be used for positive delivery reports. 250 X.1.6 Destination mailbox has moved, No forwarding address 252 The mailbox address provided was at one time valid, but mail is 253 no longer being accepted for that address. This code is only 254 useful for permanent failures. 256 X.1.7 Bad sender's mailbox address syntax 258 The sender's address was syntactically invalid. This can apply 259 to any field in the address. 261 X.1.8 Bad sender's system address 263 The sender's system specified in the address does not exist or is 264 incapable of accepting return mail. For domain names, this means 265 the address portion to the right of the "@" is invalid for mail. 267 3.3 Mailbox Status 269 X.2.0 Other or undefined mailbox status 271 The mailbox exists, but something about the destination mailbox 272 has caused the sending of this DSN. 274 X.2.1 Mailbox disabled, not accepting messages 276 The mailbox exists, but is not accepting messages. This may be a 277 permanent error if the mailbox will never be re-enabled or a 278 transient error if the mailbox is only temporarily disabled. 280 X.2.2 Mailbox full 282 The mailbox is full either because the user has exceeded an 283 administrative quota. The general semantics implies that the 284 recipient can delete messages to make more space available. This 285 code should be used as a persistent transient failure. 287 X.2.3 Message length exceeds administrative limit 289 A per-mailbox administrative message length limit has been 290 exceeded. This status code should be used when the per-mailbox 291 message length limit is less than the general system limit. This 292 code should be used as a permanent failure. 294 X.2.4 Mailing list expansion problem 296 The mailbox is a mailing list address and the mailing list was 297 unable to be expanded. This code may represent a permanent 298 failure or a persistent transient failure. 300 3.4 Mail system status 302 X.3.0 Other or undefined mail system status (3.0) 304 The destination system exists and normally accepts mail, but 305 something about the system has caused the generation of this DSN. 307 X.3.1 Mail system full 309 Mail system storage has been exceeded. The general semantics 310 imply that the individual recipient may not be able to delete 311 material to make room for additional messages. This is useful 312 only as a persistent transient error. 314 X.3.2 System not accepting network messages 316 The host on which the mailbox is resident is not accepting 317 messages. Examples of such conditions include an immanent 318 shutdown, excessive load, or system maintenance. This is useful 319 for both permanent and permanent transient errors. 321 X.3.3 System not capable of selected features 323 Selected features specified for the message are not supported by 324 the destination system. This can occur in gateways when features 325 from one domain cannot be mapped onto the supported feature in 326 another. 328 X.3.4 Message too big for system 330 The message is larger than per-message size limit. This limit 331 may either be for physical or administrative reasons. This is 332 useful only as a permanent error. 334 3.5 Network and Routing Status 336 X.4.0 Other or undefined network or routing status 338 Something went wrong with the networking, but it is not clear 339 what the problem is, or the problem cannot be well expressed with 340 any of the other provided detail codes. 342 X.4.1 No answer from host 344 The outbound connection attempt was not answered, either because 345 the remote system was busy, or otherwise unable to take a call. 346 This is useful only as a persistent transient error. 348 X.4.2 Bad connection 350 The outbound connection was established, but was otherwise unable 351 to complete the message transaction, either because of time-out, 352 or inadequate connection quality. This is useful only as a 353 persistent transient error. 355 X.4.3 Directory server failure 357 The network system was unable to forward the message, because a 358 directory server was unavailable. This is useful only as a 359 persistent transient error. 361 The inability to connect to an Internet DNS server is one example 362 of the directory server failure error. 364 X.4.4 Unable to route 366 The mail system was unable to determine the next hop for the 367 message because the necessary routing information was unavailable 368 from the directory server. This is useful for both permanent and 369 persistent transient errors. 371 A DNS lookup returning only an SOA (Start of Administration) 372 record for a domain name is one example of the unable to route 373 error. 375 X.4.5 Mail system congestion 377 The mail system was unable to deliver the message because the 378 mail system was congested. This is useful only as a persistent 379 transient error. 381 X.4.6 Routing loop detected 383 A routing loop caused the message to be forwarded too many times, 384 either because of incorrect routing tables or a user forwarding 385 loop. This is useful only as a persistent transient error. 387 X.4.7 Delivery time expired 389 The message was considered too old by the rejecting system, 390 either because it remained on that host too long or because the 391 time-to-live value specified by the sender of the message was 392 exceeded. This is useful only as a persistent transient error. 394 3.6 Mail Delivery Protocol Status 396 X.5.0 Other or undefined protocol status 398 Something was wrong with the protocol necessary to deliver the 399 message to the next hop and the problem cannot be well expressed 400 with any of the other provided detail codes. 402 X.5.1 Invalid command 404 A mail transaction protocol command was issued which was either 405 out of sequence or unsupported. This is useful only as a 406 permanent error. 408 X.5.2 Syntax error 410 A mail transaction protocol command was issued which could not be 411 interpreted, either because the syntax was wrong or the command 412 is unrecognized. This is useful only as a permanent error. 414 X.5.3 Too many recipients 416 More recipients were specified for the message than could have 417 been delivered by the protocol. This error should normally 418 result in the segmentation of the message into two, the remainder 419 of the recipients to be delivered on a subsequent delivery 420 attempt. It is included in this list in the event that such 421 segmentation is not possible. 423 X.5.4 Invalid command arguments 425 A valid mail transaction protocol command was issued with invalid 426 arguments, either because the arguments were out of range or 427 represented unrecognized features. This is useful only as a 428 permanent error. 430 X.5.5 Wrong protocol version 432 A protocol version mis-match existed which could not be 433 automatically resolved by downgrading one of the communicating 434 parties. This should never happen in ESMTP. 436 3.7 Message Content or Message Media Status 438 X.6.0 Other or undefined media error 440 Something about the content of a message caused it to be 441 considered undeliverable and the problem cannot be well expressed 442 with any of the other provided detail codes. 444 X.6.1 Media not supported 446 The media of the message is not supported by the either the 447 delivery protocol or a host in the forwarding path. This is 448 useful only as a permanent error. 450 X.6.2 Conversion required and prohibited (6.2) 452 The content of the message must be converted before it can be 453 delivered and such conversion is not permitted. Such 454 prohibitions may be the expression of the sender in the message 455 itself or the policy of the sending host. 457 X.6.3 Conversion required but not supported (6.3) 459 The message content must be converted to be forwarded but such 460 conversion is not possible or is not practical by a host in the 461 forwarding path. This condition may result when a relay supports 462 ESMTP transport but not MIME downgrade. 464 X.6.4 Conversion with loss performed 466 This is a warning sent to the sender when message delivery was 467 successfully but when the delivery required a conversion in which 468 some data was lost. 470 X.6.5 Conversion Failed 472 A conversion was required but was unsuccessful. This may be 473 useful as a permanent or persistent temporary notification. 475 3.8 Security or Policy Status 477 X.7.0 Other or undefined security status 479 Something related to security caused the message to be returned, 480 and the problem cannot be well expressed with any of the other 481 provided detail codes. This status code may also be used when 482 the condition cannot be further described because of security 483 policies in force. 485 X.7.1 Delivery not authorized, message refused 487 The sender is not authorized to send to the destination. This 488 can be the result of per-host or per-recipient filtering. This 489 memo does not discuss the merits of any such filtering, but 490 provides a mechanism to report such. This is useful only as a 491 permanent error. 493 X.7.2 Mailing list expansion prohibited 495 The sender is not authorized to send a message to the intended 496 mailing list. This is useful only as a permanent error. 498 X.7.3 Security conversion required but not possible 500 A conversion from one secure messaging protocol to another was 501 required for delivery and such conversion was not possible. This 502 is useful only as a permanent error. 504 X.7.4 Security features not supported 506 A message contained security features such as secure 507 authentication which could not be supported on the delivery 508 protocol. This is useful only as a permanent error. 510 X.7.5 Cryptographic failure 512 A transport system otherwise authorized to validate or decrypt a 513 message in transport was unable to do so because necessary 514 information such as key was not available or such information was 515 invalid. This is useful only as a permanent error. 517 X.7.6 Cryptographic algorithm not supported 519 A transport system otherwise authorized to validate or decrypt a 520 message was unable to do so because the necessary algorithm was 521 not supported. 523 X.7.7 Message integrity failure 525 A transport system otherwise authorized to validate a message was 526 unable to do so because the message was corrupted or altered. 527 This may be useful as a permanent, transient persistent, or 528 successful delivery code. 530 4. References 532 [SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821, 533 USC/Information Sciences Institute, August 1982. 535 [DSN] Moore, K., Vaudreuil, G., "An Extensible Message Format for 536 Delivery Status Notifications", Internet-Draft. 538 5. Security Consideration 540 This document describes a status code system with increased 541 precision. Use of these status codes may disclose additional 542 information about how an internal mail system is implemented beyond 543 that currently available. 545 6. Acknowledgments 547 The author wishes to offer special thank Harald Alvestrand, Marko 548 Kaittola, and Keith Moore for their extensive review and 549 constructive suggestions. 551 7. Author's Address 553 Gregory M. Vaudreuil 554 Octel Network Services 555 17060 Dallas Parkway 556 Suite 214 557 Dallas, TX 75248-1905 558 Voice/Fax: +1-214-733-2722 559 Greg.Vaudreuil@Octel.com 561 8. Appendix - Collected Status Codes 563 X.1.0 Other address status 564 X.1.1 Bad destination mailbox address 565 X.1.2 Bad destination system address 566 X.1.3 Bad destination mailbox address syntax 567 X.1.4 Destination mailbox address ambiguous 568 X.1.5 Destination mailbox address valid 569 X.1.6 Mailbox has moved 570 X.1.7 Bad sender's mailbox address syntax 571 X.1.8 Bad sender's system address 573 X.2.0 Other or undefined mailbox status 574 X.2.1 Mailbox disabled, not accepting messages 575 X.2.2 Mailbox full 576 X.2.3 Message length exceeds administrative limit. 577 X.2.4 Mailing list expansion problem 579 X.3.0 Other or undefined mail system status 580 X.3.1 Mail system full 581 X.3.2 System not accepting network messages 582 X.3.3 System not capable of selected features 583 X.3.4 Message too big for system 585 X.4.0 Other or undefined network or routing status 586 X.4.1 No answer from host 587 X.4.2 Bad connection 588 X.4.3 Routing server failure 589 X.4.4 Unable to route 590 X.4.5 Network congestion 591 X.4.6 Routing loop detected 592 X.4.7 Delivery time expired 594 X.5.0 Other or undefined protocol status 595 X.5.1 Invalid command 596 X.5.2 Syntax error 597 X.5.3 Too many recipients 598 X.5.4 Invalid command arguments 599 X.5.5 Wrong protocol version 601 X.6.0 Other or undefined media error 602 X.6.1 Media not supported 603 X.6.2 Conversion required and prohibited 604 X.6.3 Conversion required but not supported 605 X.6.4 Conversion with loss performed 606 X.6.5 Conversion failed 608 X.7.0 Other or undefined security status 609 X.7.1 Delivery not authorized, message refused 610 X.7.2 Mailing list expansion prohibited 611 X.7.3 Security conversion required but not possible 612 X.7.4 Security features not supported 613 X.7.5 Cryptographic failure 614 X.7.6 Cryptographic algorithm not supported 615 X.7.7 Message integrity failure