idnits 2.17.1 draft-ietf-appsawg-mdn-3798bis-03.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** There are 13 instances of too long lines in the document, the longest one being 13 characters in excess of 72. -- The draft header indicates that this document obsoletes RFC3798, but the abstract doesn't seem to mention this, which it should. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords -- however, there's a paragraph with a matching beginning. Boilerplate error? (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: disposition-modifier-extension Disposition modifiers may be defined in the future by later revisions or extensions to this specification. Disposition value names beginning with "X-" will never be defined as standard values; such names are reserved for experimental use. MDN disposition value names NOT beginning with "X-" MUST be registered with the Internet Assigned Numbers Authority (IANA) and described in a standards-track RFC or an experimental RFC approved by the IESG. (See Section 10 for a registration form.) MDNs with disposition modifier names not understood by the receiving MUA MAY be silently ignored or placed in the user's mailbox without special interpretation. They MUST not cause any error message to be sent to the sender of the MDN. == The document seems to contain a disclaimer for pre-RFC5378 work, but was first submitted on or after 10 November 2008. The disclaimer is usually necessary only for documents that revise or obsolete older RFCs, and that take significant amounts of text from those RFCs. If you can contact all authors of the source material and they are willing to grant the BCP78 rights to the IETF Trust, you can and should remove the disclaimer. Otherwise, the disclaimer is needed and you can ignore this comment. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (July 4, 2015) is 3218 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: 'FWS' on line 1022 ** Obsolete normative reference: RFC 3462 (ref. '6') (Obsoleted by RFC 6522) -- Obsolete informational reference (is this intentional?): RFC 3501 (ref. '13') (Obsoleted by RFC 9051) Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group T. Hansen, Ed. 3 Internet-Draft AT&T Laboratories 4 Obsoletes: 3798 (if approved) A. Melnikov, Ed. 5 Intended status: Standards Track Isode Ltd 6 Expires: January 5, 2016 July 4, 2015 8 Message Disposition Notification 9 draft-ietf-appsawg-mdn-3798bis-03.txt 11 Abstract 13 This memo defines a MIME content-type that may be used by a mail user 14 agent (MUA) or electronic mail gateway to report the disposition of a 15 message after it has been successfully delivered to a recipient. 16 This content-type is intended to be machine-processable. Additional 17 message header fields are also defined to permit Message Disposition 18 Notifications (MDNs) to be requested by the sender of a message. The 19 purpose is to extend Internet Mail to support functionality often 20 found in other messaging systems, such as X.400 and the proprietary 21 "LAN-based" systems, and often referred to as "read receipts," 22 "acknowledgements", or "receipt notifications." The intention is to 23 do this while respecting privacy concerns, which have often been 24 expressed when such functions have been discussed in the past. 26 Because many messages are sent between the Internet and other 27 messaging systems (such as X.400 or the proprietary "LAN-based" 28 systems), the MDN protocol is designed to be useful in a multi- 29 protocol messaging environment. To this end, the protocol described 30 in this memo provides for the carriage of "foreign" addresses, in 31 addition to those normally used in Internet Mail. Additional 32 attributes may also be defined to support "tunneling" of foreign 33 notifications through Internet Mail. 35 Status of This Memo 37 This Internet-Draft is submitted in full conformance with the 38 provisions of BCP 78 and BCP 79. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF). Note that other groups may also distribute 42 working documents as Internet-Drafts. The list of current Internet- 43 Drafts is at http://datatracker.ietf.org/drafts/current/. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 This Internet-Draft will expire on January 5, 2016. 51 Copyright Notice 53 Copyright (c) 2015 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (http://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the Simplified BSD License. 66 This document may contain material from IETF Documents or IETF 67 Contributions published or made publicly available before November 68 10, 2008. The person(s) controlling the copyright in some of this 69 material may not have granted the IETF Trust the right to allow 70 modifications of such material outside the IETF Standards Process. 71 Without obtaining an adequate license from the person(s) controlling 72 the copyright in such materials, this document may not be modified 73 outside the IETF Standards Process, and derivative works of it may 74 not be created outside the IETF Standards Process, except to format 75 it for publication as an RFC or to translate it into languages other 76 than English. 78 Table of Contents 80 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 81 1.1. Purposes . . . . . . . . . . . . . . . . . . . . . . . . 3 82 1.2. Requirements . . . . . . . . . . . . . . . . . . . . . . 4 83 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 84 2. Requesting Message Disposition Notifications . . . . . . . . 5 85 2.1. The Disposition-Notification-To Header . . . . . . . . . 5 86 2.2. The Disposition-Notification-Options Header . . . . . . . 7 87 2.3. The Original-Recipient Header Field . . . . . . . . . . . 8 88 2.4. Use with the Message/Partial Content Type . . . . . . . . 9 89 3. Format of a Message Disposition Notification . . . . . . . . 9 90 3.1. The message/disposition-notification content-type . . . . 11 91 3.2. Message/disposition-notification Fields . . . . . . . . . 13 92 3.3. Extension-fields . . . . . . . . . . . . . . . . . . . . 18 93 4. Timeline of events . . . . . . . . . . . . . . . . . . . . . 19 94 5. Conformance and Usage Requirements . . . . . . . . . . . . . 20 95 6. Security Considerations . . . . . . . . . . . . . . . . . . . 20 96 6.1. Forgery . . . . . . . . . . . . . . . . . . . . . . . . . 21 97 6.2. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 21 98 6.3. Non-Repudiation . . . . . . . . . . . . . . . . . . . . . 22 99 6.4. Mail Bombing . . . . . . . . . . . . . . . . . . . . . . 22 100 7. Collected ABNF Grammar . . . . . . . . . . . . . . . . . . . 22 101 8. Guidelines for Gatewaying MDNs . . . . . . . . . . . . . . . 24 102 8.1. Gatewaying from other mail systems to MDNs . . . . . . . 24 103 8.2. Gatewaying from MDNs to other mail systems . . . . . . . 25 104 8.3. Gatewaying of MDN-requests to other mail systems . . . . 25 105 9. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 106 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 107 10.1. Disposition-Notification-Options header field 108 disposition-notification-parameter names . . . . . . . . 27 109 10.2. Disposition modifier names . . . . . . . . . . . . . . . 28 110 10.3. MDN extension field names . . . . . . . . . . . . . . . 28 111 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 112 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 29 113 12.1. Normative References . . . . . . . . . . . . . . . . . . 29 114 12.2. Informative References . . . . . . . . . . . . . . . . . 29 115 Appendix A. Changes from RFC 3798 . . . . . . . . . . . . . . . 30 116 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 118 1. Introduction 120 This memo defines a RFC-MIME-MEDIA [4] content-type for message 121 disposition notifications (MDNs). An MDN can be used to notify the 122 sender of a message of any of several conditions that may occur after 123 successful delivery, such as display of the message contents, 124 printing of the message, deletion (without display) of the message, 125 or the recipient's refusal to provide MDNs. The "message/ 126 disposition-notification" content-type defined herein is intended for 127 use within the framework of the "multipart/report" content type 128 defined in RFC-REPORT [6]. 130 This memo defines the format of the notifications and the RFC-MSGFMT 131 [2] header fields used to request them. 133 This memo is an update to RFC 3798 and is intended to be published at 134 Internet Standard Level. 136 This memo is currently marked with the 'pre5378Trust200902' IPR 137 statements until a release has been obtained from all previous 138 authors and editors of this text. 140 1.1. Purposes 142 The MDNs defined in this memo are expected to serve several purposes: 144 a. Inform human beings of the disposition of messages after 145 successful delivery, in a manner that is largely independent of 146 human language; 148 b. Allow mail user agents to keep track of the disposition of 149 messages sent, by associating returned MDNs with earlier message 150 transmissions; 152 c. Convey disposition notification requests and disposition 153 notifications between Internet Mail and "foreign" mail systems 154 via a gateway; 156 d. Allow "foreign" notifications to be tunneled through a MIME- 157 capable message system and back into the original messaging 158 system that issued the original notification, or even to a third 159 messaging system; 161 e. Allow language-independent, yet reasonably precise, indications 162 of the disposition of a message to be delivered. 164 1.2. Requirements 166 These purposes place the following constraints on the notification 167 protocol: 169 a. It must be readable by humans, and must be machine-parsable. 171 b. It must provide enough information to allow message senders (or 172 their user agents) to unambiguously associate an MDN with the 173 message that was sent and the original recipient address for 174 which the MDN was issued (if such information is available), even 175 if the message was forwarded to another recipient address. 177 c. It must also be able to describe the disposition of a message 178 independent of any particular human language or of the 179 terminology of any particular mail system. 181 d. The specification must be extensible in order to accommodate 182 future requirements. 184 1.3. Terminology 186 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 187 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 188 document are to be interpreted as described in RFC-KEYWORDS [9]. 190 All syntax descriptions use the ABNF specified by RFC-MSGFMT [2], in 191 which the lexical tokens (used below) are defined: "CRLF", "FWS", 192 "CFWS", "field-name", "mailbox", "msg-id", and "text". The following 193 lexical tokens are defined in RFC-SMTP [1]: "atom". The following 194 lexical tokens are defined in the definition of the Content-Type 195 header field in RFC-MIME-BODY [3]: "attribute" and "value". 197 2. Requesting Message Disposition Notifications 199 Message disposition notifications are requested by including a 200 Disposition-Notification-To header field in the message containing 201 one or more addresses specifying where dispositions should be sent. 202 Further information to be used by the recipient's MUA in generating 203 the MDN may be provided by also including Original-Recipient and/or 204 Disposition-Notification-Options header fields in the message. 206 2.1. The Disposition-Notification-To Header 208 A request for the receiving user agent to issue message disposition 209 notifications is made by placing a Disposition-Notification-To header 210 field into the message. The syntax of the header field is 212 mdn-request-header = "Disposition-Notification-To" ":" [FWS] 213 mailbox *("," [FWS] mailbox) 215 The presence of a Disposition-Notification-To header field in a 216 message is merely a request for an MDN. The recipients' user agents 217 are always free to silently ignore such a request. 219 An MDN MUST NOT itself have a Disposition-Notification-To header 220 field. An MDN MUST NOT be generated in response to an MDN. 222 A user agent MUST NOT issue more than one MDN on behalf of each 223 particular recipient. That is, once an MDN has been issued on behalf 224 of a recipient, no further MDNs may be issued on behalf of that 225 recipient by the same user agent, even if another disposition is 226 performed on the message. However, if a message is forwarded, an MDN 227 may have been issued for the recipient doing the forwarding and the 228 recipient of the forwarded message may also cause an MDN to be 229 generated. 231 It is also possible that if the same message is being accessed by 232 multiple user agents (for example using POP3), then multiple 233 dispositions might be generated for the same recipient. User agents 234 SHOULD laverage support in the underlying message access protocol to 235 prevent multiple MDNs from being generated. In particular, when the 236 user agent is accessing the message using RFC-IMAP [13], it SHOULD 237 implement the procedures specified in RFC-IMAP-MDN [10]. 239 While Internet standards normally do not specify the behavior of user 240 interfaces, it is strongly recommended that the user agent obtain the 241 user's consent before sending an MDN. This consent could be obtained 242 for each message through some sort of prompt or dialog box, or 243 globally through the user's setting of a preference. 245 MDNs SHOULD NOT be sent automatically if the address in the 246 Disposition-Notification-To header field differs from the address in 247 the Return-Path header field (see RFC-MSGFMT [2]). In this case, 248 confirmation from the user SHOULD be obtained, if possible. If 249 obtaining consent is not possible (e.g., because the user is not 250 online at the time), then an MDN SHOULD NOT be sent. 252 Confirmation from the user SHOULD be obtained (or no MDN sent) if 253 there is no Return-Path header field in the message, or if there is 254 more than one distinct address in the Disposition-Notification-To 255 header field. 257 The comparison of the addresses should be done using only the addr- 258 spec (local-part "@" domain) portion, excluding any angle brackets, 259 phrase and route. The comparison MUST be case-sensitive for the 260 local-part and case-insensitive for the domain part. The local-part 261 comparison SHOULD be done after performing local-part 262 canonicalization (i.e. after removing the surrounding double-quote 263 characters, if any, as well as any escaping "\" characters. (See 264 RFC-MSGFMT [2] for more details.) Implementations MAY treat known 265 domain aliases as equivalent for the purpose of comparison. 267 Note that use of subaddressing (see [12]) can result in a failure to 268 match two local-parts and thus result in possible suppression of the 269 MDN. This document doesn't recommend special handling for this case, 270 as the receiving MUA can't reliably know whether or not the sender is 271 using subaddressing. [[ more work needed here ]] 273 [[CREF1: (From Bruce) Of those, the angle bracket issue ought to be 274 understood, but clarification could benefit implementors, especially 275 as RFC 5322 defined the Return-Path syntax somewhat peculiarly. 276 Canonicalization of local-parts and domains should probably be 277 required prior to comparison, and use of on-the-wire forms should 278 probably also be specified. DNS equivalence issues might be tricky 279 for some implementations (e.g. offline reading); perhaps the 280 specification could use RFC 2119 "MAY" to give implementations leeway 281 to consider A vs. CNAME and DNS vs domain literal equivalence for 282 situations where DNS is available to the implementation (I'm not sure 283 about MX). About the only thing that can be said w.r.t. 284 subaddressing and subdomains is a caution to sending MUA and address- 285 rewriting MTA authors that a mismatch might result in no MDN being 286 produced. ]] 288 If the message contains more than one Return-Path header field, the 289 implementation may pick one to use for the comparison, or treat the 290 situation as a failure of the comparison. 292 The reason for not automatically sending an MDN if the comparison 293 fails or more than one address is specified is to reduce the 294 possibility of mail loops and of MDNs being used for mail bombing. 296 A message that contains a Disposition-Notification-To header field 297 SHOULD also contain a Message-ID header field as specified in RFC- 298 MSGFMT [2]. This will permit automatic correlation of MDNs with 299 their original messages by user agents. 301 If the request for message disposition notifications for some 302 recipients and not others is desired, two copies of the message 303 should be sent, one with a Disposition-Notification-To header field 304 and one without. Many of the other header fields of the message 305 (e.g., To, Cc) will be the same in both copies. The recipients in 306 the respective message envelopes determine for whom message 307 disposition notifications are requested and for whom they are not. 308 If desired, the Message-ID header field may be the same in both 309 copies of the message. Note that there are other situations (e.g., 310 Bcc) in which it is necessary to send multiple copies of a message 311 with slightly different header fields. The combination of such 312 situations and the need to request MDNs for a subset of all 313 recipients may result in more than two copies of a message being 314 sent, some with a Disposition-Notification-To header field and some 315 without. 317 Messages posted to newsgroups SHOULD NOT have a Disposition- 318 Notification-To header field. 320 2.2. The Disposition-Notification-Options Header 322 Future extensions to this specification may require that information 323 be supplied to the recipient's MUA for additional control over how 324 and what MDNs are generated. The Disposition-Notification-Options 325 header field provides an extensible mechanism for such information. 326 The syntax of this header field is as follows: 328 Disposition-Notification-Options = 329 "Disposition-Notification-Options" ":" [FWS] 330 disposition-notification-parameter-list 331 disposition-notification-parameter-list = 332 disposition-notification-parameter 333 *(";" [FWS] disposition-notification-parameter) 334 disposition-notification-parameter = attribute [FWS] "=" 335 [FWS] importance [FWS] "," [FWS] value *([FWS] "," [FWS] value) 336 importance = "required" / "optional" 338 An importance of "required" indicates that interpretation of the 339 disposition-notification-parameter is necessary for proper generation 340 of an MDN in response to this request. An importance of "optional" 341 indicates that an MUA that does not understand the meaning of this 342 disposition-notification-parameter MAY generate an MDN in response 343 anyway, ignoring the value of the disposition-notification-parameter. 345 No disposition-notification-parameter attribute names are defined in 346 this specification. Attribute names may be defined in the future by 347 later revisions or extensions to this specification. Disposition- 348 notification-parameter attribute names beginning with "X-" will never 349 be defined as standard names; such names are reserved for 350 experimental use. disposition-notification-parameter attribute names 351 not beginning with "X-" MUST be registered with the Internet Assigned 352 Numbers Authority (IANA) and described in a standards-track RFC or an 353 experimental RFC approved by the IESG. [[ more work needed here ]] 354 (See Section 10 for a registration form.) 356 2.3. The Original-Recipient Header Field 358 Since electronic mail addresses may be rewritten while the message is 359 in transit, it is useful for the original recipient address to be 360 made available by the delivering MTA. The delivering MTA may be able 361 to obtain this information from the ORCPT parameter of the SMTP RCPT 362 TO command, as defined in RFC-SMTP [1] and RFC-DSN-SMTP [7]. 364 RFC-DSN-SMTP [7] is amended as follows: If the ORCPT information is 365 available, the delivering MTA SHOULD insert an Original-Recipient 366 header field at the beginning of the message (along with the Return- 367 Path header field). The delivering MTA MAY delete any other 368 Original-Recipient header fields that occur in the message. The 369 syntax of this header field is as follows: 371 original-recipient-header = 372 "Original-Recipient" ":" [FWS] address-type [FWS] ";" [FWS] generic-address 374 The address-type and generic-address token are as specified in the 375 description of the Original-Recipient field in Section 3.2.3. 377 The purpose of carrying the original recipient information and 378 returning it in the MDN is to permit automatic correlation of MDNs 379 with the original message on a per-recipient basis. 381 2.4. Use with the Message/Partial Content Type 383 The use of the header fields Disposition-Notification-To, 384 Disposition-Notification-Options, and Original-Recipient with the 385 MIME message/partial content type (RFC-MIME-MEDIA [4]]) requires 386 further definition. 388 When a message is segmented into two or more message/partial 389 fragments, the three header fields mentioned in the above paragraph 390 SHOULD be placed in the "inner" or "enclosed" message (using the 391 terms of RFC-MIME-MEDIA [4]). These header fields SHOULD NOT be used 392 in the header fields of any of the fragments themselves. 394 When the multiple message/partial fragments are reassembled, the 395 following applies. If these header fields occur along with the other 396 header fields of a message/partial fragment message, they pertain to 397 an MDN that will be generated for the fragment. If these header 398 fields occur in the header fields of the "inner" or "enclosed" 399 message (using the terms of RFC-MIME-MEDIA [4]), they pertain to an 400 MDN that will be generated for the reassembled message. 401 Section 5.2.2.1 of RFC-MIME-MEDIA [4]) is amended to specify that, in 402 addition to the header fields specified there, the three header 403 fields described in this specification are to be appended, in order, 404 to the header fields of the reassembled message. Any occurrences of 405 the three header fields defined here in the header fields of the 406 initial enclosing message must not be copied to the reassembled 407 message. 409 3. Format of a Message Disposition Notification 411 A message disposition notification is a MIME message with a top-level 412 content-type of multipart/report (defined in RFC-REPORT [6]). When 413 multipart/report content is used to transmit an MDN: 415 a. The report-type parameter of the multipart/report content is 416 "disposition-notification". 418 b. The first component of the multipart/report contains a human- 419 readable explanation of the MDN, as described in RFC-REPORT [6]. 421 c. The second component of the multipart/report is of content-type 422 message/disposition-notification, described in Section 3.1 of 423 this document. 425 d. If the original message or a portion of the message is to be 426 returned to the sender, it appears as the third component of the 427 multipart/report. The decision of whether or not to return the 428 message or part of the message is up to the MUA generating the 429 MDN. However, in the case of encrypted messages requesting MDNs, 430 encrypted message text MUST be returned, if it is returned at 431 all, only in its original encrypted form. 433 NOTE: For message disposition notifications gatewayed from foreign 434 systems, the header fields of the original message may not be 435 available. In this case, the third component of the MDN may be 436 omitted, or it may contain "simulated" RFC-MSGFMT [2] header fields 437 that contain equivalent information. In particular, it is very 438 desirable to preserve the subject and date fields from the original 439 message. 441 The MDN MUST be addressed (in both the message header field and the 442 transport envelope) to the address(es) from the Disposition- 443 Notification-To header field from the original message for which the 444 MDN is being generated. 446 The From field of the message header field of the MDN MUST contain 447 the address of the person for whom the message disposition 448 notification is being issued. 450 The envelope sender address (i.e., SMTP MAIL FROM) of the MDN MUST be 451 null (<>), specifying that no Delivery Status Notification messages 452 or other messages indicating successful or unsuccessful delivery are 453 to be sent in response to an MDN. 455 A message disposition notification MUST NOT itself request an MDN. 456 That is, it MUST NOT contain a Disposition-Notification-To header 457 field. 459 The Message-ID header field (if present) for an MDN MUST be different 460 from the Message-ID of the message for which the MDN is being issued. 462 A particular MDN describes the disposition of exactly one message for 463 exactly one recipient. Multiple MDNs may be generated as a result of 464 one message submission, one per recipient. However, due to the 465 circumstances described in Section 2.1, MDNs may not be generated for 466 some recipients for which MDNs were requested. 468 3.1. The message/disposition-notification content-type 470 The message/disposition-notification content-type is defined as 471 follows: 473 MIME type name: message 475 MIME subtype name: disposition-notification 477 Optional parameters: none 479 Encoding considerations: "7bit" encoding is sufficient and MUST be 480 used to maintain readability when viewed by non- 481 MIME mail readers. 483 Security considerations: discussed in Section 6 of this memo. 485 (While the 7bit restriction applies to the message/disposition- 486 notification portion of the multipart/report content, it does not 487 apply to the optional third portion of the multipart/report content.) 489 The message/disposition-notification report type for use in the 490 multipart/report is "disposition-notification". 492 The body of a message/disposition-notification consists of one or 493 more "fields" formatted according to the ABNF of RFC-MSGFMT [2] 494 header "fields". The syntax of the message/disposition-notification 495 content is as follows: 497 disposition-notification-content = [ reporting-ua-field CRLF ] 498 [ mdn-gateway-field CRLF ] 499 [ original-recipient-field CRLF ] 500 final-recipient-field CRLF 501 [ original-message-id-field CRLF ] 502 disposition-field CRLF 503 *( failure-field CRLF ) 504 *( error-field CRLF ) 505 *( extension-field CRLF ) 506 extension-field = extension-field-name ":" *(FWS / text) 507 extension-field-name = field-name 509 Note that the order of the above fields is fixed, with the exception 510 of the extension fields. 512 3.1.1. General conventions for fields 514 Since these fields are defined according to the rules of RFC-MSGFMT 515 [2], the same conventions for continuation lines and comments apply. 516 Notification fields may be continued onto multiple lines by beginning 517 each additional line with a SPACE or HTAB. Text that appears in 518 parentheses is considered a comment and not part of the contents of 519 that notification field. Field names are case-insensitive, so the 520 names of notification fields may be spelled in any combination of 521 upper and lower case letters. Comments in notification fields may 522 use the "encoded-word" construct defined in RFC-MIME-HEADER [5]. 524 3.1.2. "*-type" subfields 526 Several fields consist of a "-type" subfield, followed by a semi- 527 colon, followed by "*text". 528 [[CREF2: (Here and elsewhere in the document) It looks like there is 529 emerging consensus that the document should describe 2 grammars: one 530 for "must accept" (which either allows CFWS or [FWS]) and another one 531 for "should generate" (CFWS not allowed, but *WSP are allowed). A 532 future version of this document will implement this change, unless 533 objections are voiced. ]] 534 For these fields, the keyword used in the address-type or MTA-type 535 subfield indicates the expected format of the address or MTA-name 536 that follows. 538 The "-type" subfields are defined as follows: 540 a. An "address-type" specifies the format of a mailbox address. For 541 example, Internet Mail addresses use the "rfc822" address-type. 543 address-type = atom 544 atom = 546 b. An "MTA-name-type" specifies the format of a mail transfer agent 547 name. For example, for an SMTP server on an Internet host, the 548 MTA name is the domain name of that host, and the "dns" MTA-name- 549 type is used. 551 mta-name-type = atom 553 Values for address-type and mta-name-type are case-insensitive. 554 Thus, address-type values of "RFC822" and "rfc822" are equivalent. 556 The Internet Assigned Numbers Authority (IANA) maintains a registry 557 of address-type and mta-name-type values, along with descriptions of 558 the meanings of each, or a reference to one or more specifications 559 that provide such descriptions. (The "rfc822" address-type is 560 defined in RFC-DSN-SMTP [7].) Registration forms for address-type 561 and mta-name-type appear in RFC-DSN-FORMAT [8]. 563 3.2. Message/disposition-notification Fields 565 3.2.1. The Reporting-UA field 567 reporting-ua-field = "Reporting-UA" ":" OWS ua-name OWS [ ";" OWS ua-product OWS ] 568 ua-name = *text-no-semi 569 ua-product = *(FWS / text) 570 text-no-semi = %d1-9 / ; "text" characters excluding NUL, CR, 571 %d11 / %d12 / %d14-58 / %d60-127 ; LF, or semi-colon 572 OWS = *WSP 573 ; Optional whitespace. 574 ; MDN generators SHOULD use "*WSP" 575 ; (typically a single space or nothing. 576 ; It SHOULD be nothing at the end of a field). 577 ; MDN parsers MUST parse it as "[CFWS]". 579 The Reporting-UA field is defined as follows: 581 An MDN describes the disposition of a message after it has been 582 delivered to a recipient. In all cases, the Reporting-UA is the MUA 583 that performed the disposition described in the MDN. This field is 584 optional, but recommended. For Internet Mail user agents, it is 585 recommended that this field contain both: the DNS name of the 586 particular instance of the MUA that generated the MDN, and the name 587 of the product. For example, 589 Reporting-UA: pc.example.com; Foomail 97.1 591 If the reporting MUA consists of more than one component (e.g., a 592 base program and plug-ins), this may be indicated by including a list 593 of product names. [[CREF3: Should ua-name be defined as "*(FWS / 594 text-no-semi)"?]] 596 3.2.2. The MDN-Gateway field 598 The MDN-Gateway field indicates the name of the gateway or MTA that 599 translated a foreign (non-Internet) message disposition notification 600 into this MDN. This field MUST appear in any MDN that was translated 601 by a gateway from a foreign system into MDN format, and MUST NOT 602 appear otherwise. 604 mdn-gateway-field = "MDN-Gateway" ":" OWS mta-name-type OWS ";" OWS mta-name OWS 605 mta-name = *text 606 For gateways into Internet Mail, the MTA-name-type will normally be 607 "smtp", and the mta-name will be the Internet domain name of the 608 gateway. 610 3.2.3. Original-Recipient field 612 The Original-Recipient field indicates the original recipient address 613 as specified by the sender of the message for which the MDN is being 614 issued. For Internet Mail messages, the value of the Original- 615 Recipient field is obtained from the Original-Recipient header field 616 from the message for which the MDN is being generated. If there is 617 no Original-Recipient header field in the message, then the Original- 618 Recipient field MUST be omitted, unless the same information is 619 reliably available some other way. If there is an Original-Recipient 620 header field in the original message (or original recipient 621 information is reliably available some other way), then the Original- 622 Recipient field must be supplied. If there is more than one 623 Original-Recipient header field in the message, the MUA may choose 624 the one to use, or act as if no Original-Recipient header field is 625 present. 627 original-recipient-field = 628 "Original-Recipient" ":" OWS address-type OWS ";" OWS generic-address OWS 629 generic-address = *text 631 The address-type field indicates the type of the original recipient 632 address. If the message originated within the Internet, the address- 633 type field will normally be "rfc822", and the address will be 634 according to the syntax specified in RFC-MSGFMT [2]. The value 635 "unknown" should be used if the Reporting MUA cannot determine the 636 type of the original recipient address from the message envelope. 637 This address is the same as that provided by the sender and can be 638 used to automatically correlate MDN reports with original messages on 639 a per recipient basis. 641 3.2.4. Final-Recipient field 643 The Final-Recipient field indicates the recipient for which the MDN 644 is being issued. This field MUST be present. 646 The syntax of the field is as follows: 648 final-recipient-field = 649 "Final-Recipient" ":" OWS address-type OWS ";" OWS generic-address OWS 651 The generic-address subfield of the Final-Recipient field MUST 652 contain the mailbox address of the recipient (from the From header 653 field of the MDN) as it was when the MDN was generated by the MUA. 655 The Final-Recipient address may differ from the address originally 656 provided by the sender, because it may have been transformed during 657 forwarding and gatewaying into a totally unrecognizable mess. 658 However, in the absence of the optional Original-Recipient field, the 659 Final-Recipient field and any returned content may be the only 660 information available with which to correlate the MDN with a 661 particular message recipient. 663 The address-type subfield indicates the type of address expected by 664 the reporting MTA in that context. Recipient addresses obtained via 665 SMTP will normally be of address-type "rfc822". 667 Since mailbox addresses (including those used in the Internet) may be 668 case sensitive, the case of alphabetic characters in the address MUST 669 be preserved. 671 3.2.5. Original-Message-ID field 673 The Original-Message-ID field indicates the message-ID of the message 674 for which the MDN is being issued. It is obtained from the Message- 675 ID header field of the message for which the MDN is issued. This 676 field MUST be present if the original message contained a Message-ID 677 header field. The syntax of the field is as follows: 679 original-message-id-field = 680 "Original-Message-ID" ":" OWS msg-id OWS 682 The msg-id token is as specified in RFC-MSGFMT [2]. 684 3.2.6. Disposition field 686 The Disposition field indicates the action performed by the 687 Reporting-MUA on behalf of the user. This field MUST be present. 689 The syntax for the Disposition field is: 691 disposition-field = 692 "Disposition" ":" OWS disposition-mode OWS ";" 693 OWS disposition-type 694 [ OWS "/" OWS disposition-modifier 695 *( OWS "," OWS disposition-modifier ) ] OWS 696 disposition-mode = action-mode OWS "/" OWS sending-mode 697 action-mode = "manual-action" / "automatic-action" 698 sending-mode = "MDN-sent-manually" / "MDN-sent-automatically" 699 disposition-type = "displayed" / "deleted" / "dispatched" / 700 "processed" 701 disposition-modifier = "error" / disposition-modifier-extension 702 disposition-modifier-extension = atom 703 The disposition-mode, disposition-type, and disposition-modifier may 704 be spelled in any combination of upper and lower case characters. 706 3.2.6.1. Disposition modes 708 The following disposition modes are defined: 710 "manual-action" The disposition described by the disposition type 711 was a result of an explicit instruction by the 712 user rather than some sort of automatically 713 performed action. 715 "automatic-action" The disposition described by the disposition type 716 was a result of an automatic action, rather than 717 an explicit instruction by the user for this 718 message. 720 "Manual-action" and "automatic-action" are mutually exclusive. One 721 or the other MUST be specified. 723 "MDN-sent-manually" The user explicitly gave permission for this 724 particular MDN to be sent. 726 "MDN-sent-automatically" The MDN was sent because the MUA had 727 previously been configured to do so 728 automatically. 730 "MDN-sent-manually" and "MDN-sent-automatically" are mutually 731 exclusive. One or the other MUST be specified. 733 3.2.6.2. Disposition types 735 The following disposition-types are defined: 737 "displayed" The message has been displayed by the MUA to 738 someone reading the recipient's mailbox. There 739 is no guarantee that the content has been read or 740 understood. 742 "dispatched" The message has been sent somewhere in some 743 manner (e.g., printed, faxed, forwarded) without 744 necessarily having been previously displayed to 745 the user. The user may or may not see the 746 message later. 748 "processed" The message has been processed in some manner 749 (i.e., by some sort of rules or server) without 750 being displayed to the user. The user may or may 751 not see the message later, or there may not even 752 be a human user associated with the mailbox. 754 "deleted" The message has been deleted. The recipient may 755 or may not have seen the message. The recipient 756 might "undelete" the message at a later time and 757 read the message. 759 3.2.6.3. Disposition modifiers 761 Only the extension disposition modifiers is defined: 763 disposition-modifier-extension 764 Disposition modifiers may be defined in the 765 future by later revisions or extensions to this 766 specification. Disposition value names beginning 767 with "X-" will never be defined as standard 768 values; such names are reserved for experimental 769 use. MDN disposition value names NOT beginning 770 with "X-" MUST be registered with the Internet 771 Assigned Numbers Authority (IANA) and described 772 in a standards-track RFC or an experimental RFC 773 approved by the IESG. (See Section 10 for a 774 registration form.) MDNs with disposition 775 modifier names not understood by the receiving 776 MUA MAY be silently ignored or placed in the 777 user's mailbox without special interpretation. 778 They MUST not cause any error message to be sent 779 to the sender of the MDN. 781 If an MUA developer does not wish to register the meanings of such 782 disposition modifier extensions, "X-" modifiers may be used for this 783 purpose. To avoid name collisions, the name of the MUA 784 implementation should follow the "X-", (e.g., "X-Foomail-"). 786 It is not required that an MUA be able to generate all of the 787 possible values of the Disposition field. 789 A user agent MUST NOT issue more than one MDN on behalf of each 790 particular recipient. That is, once an MDN has been issued on behalf 791 of a recipient, no further MDNs may be issued on behalf of that 792 recipient, even if another disposition is performed on the message. 793 However, if a message is forwarded, a "dispatched" MDN MAY be issued 794 for the recipient doing the forwarding and the recipient of the 795 forwarded message may also cause an MDN to be generated. 797 3.2.7. Failure and Error Fields 799 The Failure and Error fields are used to supply additional 800 information in the form of text messages when the "failure" 801 disposition type or "error" disposition modifier appear. The syntax 802 is as follows: 804 failure-field = "Failure" ":" *(FWS / text) 805 error-field = "Error" ":" *(FWS / text) 807 3.3. Extension-fields 809 Additional MDN fields may be defined in the future by later revisions 810 or extensions to this specification. Extension-field names beginning 811 with "X-" will never be defined as standard fields; such names are 812 reserved for experimental use. MDN field names NOT beginning with 813 "X-" MUST be registered with the Internet Assigned Numbers Authority 814 (IANA) and described in a standards-track RFC or an experimental RFC 815 approved by the IESG. (See Section 10 for a registration form.) MDN 816 Extension-fields may be defined for the following reasons: 818 a. To allow additional information from foreign disposition reports 819 to be tunneled through Internet MDNs. The names of such MDN 820 fields should begin with an indication of the foreign environment 821 name (e.g., X400-Physical-Forwarding-Address). 823 b. To allow transmission of diagnostic information that is specific 824 to a particular mail user agent (MUA). The names of such MDN 825 fields should begin with an indication of the MUA implementation 826 that produced the MDN (e.g., Foomail-information). 828 If an application developer does not wish to register the meanings of 829 such extension fields, "X-" fields may be used for this purpose. To 830 avoid name collisions, the name of the application implementation 831 should follow the "X-", (e.g., "X-Foomail-Log-ID" or "X-Foomail-EDI- 832 info"). 834 4. Timeline of events 836 The following timeline shows when various events in the processing of 837 a message and generation of MDNs take place: 839 -- User composes message 841 -- User tells MUA to send message 843 -- MUA passes message to MTA (original recipient information passed 844 along) 846 -- MTA sends message to next MTA 848 -- Final MTA receives message 850 -- Final MTA delivers message to MUA (possibly generating a DSN) 852 -- MUA performs automatic processing and generates corresponding MDNs 853 ("dispatched", "processed" or "deleted" disposition type with 854 "automatic-action" and "MDN-sent-automatically" disposition modes) 856 -- MUA displays list of messages to user 858 -- User selects a message and requests that some action be performed 859 on it. 861 -- MUA performs requested action and, with user's permission, sends 862 an appropriate MDN ("displayed", "dispatched", "processed", or 863 "deleted" disposition type, with "manual-action" and "MDN-sent- 864 manually" or "MDN-sent-automatically" disposition mode). 866 -- User possibly performs other actions on message, but no further 867 MDNs are generated. 869 5. Conformance and Usage Requirements 871 An MUA or gateway conforms to this specification if it generates MDNs 872 according to the protocol defined in this memo. It is not necessary 873 to be able to generate all of the possible values of the Disposition 874 field. 876 MUAs and gateways MUST NOT generate the Original-Recipient field of 877 an MDN unless the mail protocols provide the address originally 878 specified by the sender at the time of submission. Ordinary SMTP 879 does not make that guarantee, but the SMTP extension defined in RFC- 880 DSN-SMTP [7] permits such information to be carried in the envelope 881 if it is available. The Original-Recipient header field defined in 882 this document provides a way for the MTA to pass the original 883 recipient address to the MUA. 885 Each sender-specified recipient address may result in more than one 886 MDN. If an MDN is requested for a recipient that is forwarded to 887 multiple recipients of an "alias" (as defined in RFC-DSN-SMTP [7], 888 section 6.2.7.3), each of the recipients may issue an MDN. 890 Successful distribution of a message to a mailing list exploder 891 SHOULD be considered the final disposition of the message. A mailing 892 list exploder MAY issue an MDN with a disposition type of "processed" 893 and disposition modes of "automatic-action" and "MDN-sent- 894 automatically" indicating that the message has been forwarded to the 895 list. In this case, the request for MDNs is not propagated to the 896 members of the list. 898 Alternatively, the mailing list exploder MAY issue no MDN and 899 propagate the request for MDNs to all members of the list. The 900 latter behavior is not recommended for any but small, closely knit 901 lists, as it might cause large numbers of MDNs to be generated and 902 may cause confidential subscribers to the list to be revealed. The 903 mailing list exploder MAY also direct MDNs to itself, correlate them, 904 and produce a report to the original sender of the message. 906 This specification places no restrictions on the processing of MDNs 907 received by user agents or mailing lists. 909 6. Security Considerations 911 The following security considerations apply when using MDNs: 913 6.1. Forgery 915 MDNs may be forged as easily as ordinary Internet electronic mail. 916 User agents and automatic mail handling facilities (such as mail 917 distribution list exploders) that wish to make automatic use of MDNs 918 should take appropriate precautions to minimize the potential damage 919 from denial-of-service attacks. 921 Security threats related to forged MDNs include the sending of: 923 a. A falsified disposition notification when the indicated 924 disposition of the message has not actually occurred, 926 b. Unsolicited MDNs 928 6.2. Privacy 930 Another dimension of security is privacy. There may be cases in 931 which a message recipient does not wish the disposition of messages 932 addressed to him to be known, or is concerned that the sending of 933 MDNs may reveal other sensitive information (e.g., when the message 934 was read). In this situation, it is acceptable for the MUA to 935 silently ignore requests for MDNs. 937 If the Disposition-Notification-To header field is passed on 938 unmodified when a message is distributed to the subscribers of a 939 mailing list, the subscribers to the list may be revealed to the 940 sender of the original message by the generation of MDNs. 942 Headers of the original message returned in part 3 of the multipart/ 943 report could reveal confidential information about host names and/or 944 network topology inside a firewall. 946 An unencrypted MDN could reveal confidential information about an 947 encrypted message, especially if all or part of the original message 948 is returned in part 3 of the multipart/report. Encrypted MDNs are 949 not defined in this specification. 951 In general, any optional MDN field may be omitted if the Reporting 952 MUA site or user determines that inclusion of the field would impose 953 too great a compromise of site confidentiality. The need for such 954 confidentiality must be balanced against the utility of the omitted 955 information in MDNs. 957 In some cases, someone with access to the message stream may use the 958 MDN request mechanism to monitor the mail reading habits of a target. 960 If the target is known to generate MDN reports, they could add a 961 disposition-notification-to field containing the envelope from 962 address along with a source route. The source route is ignored in 963 the comparison so the addresses will always match. But if the source 964 route is honored when the notification is sent, it could direct the 965 message to some other destination. This risk can be minimized by not 966 sending MDN's automatically. 968 6.3. Non-Repudiation 970 MDNs do not provide non-repudiation with proof of delivery. Within 971 the framework of today's Internet Mail, the MDNs defined in this 972 document provide valuable information to the mail user; however, MDNs 973 cannot be relied upon as a guarantee that a message was or was not 974 seen by the recipient. Even if MDNs are not actively forged, they 975 may be lost in transit. The recipient may bypass the MDN issuing 976 mechanism in some manner. 978 One possible solution for this purpose can be found in RFC-SEC- 979 SERVICES [11]. 981 6.4. Mail Bombing 983 The MDN request mechanism introduces an additional way of mailbombing 984 a mailbox. The MDN request notification provides an address to which 985 MDN's should be sent. It is possible for an attacking agent to send 986 a potentially large set of messages to otherwise unsuspecting third 987 party recipients with a false "disposition-notification-to:" address. 988 Automatic, or simplistic processing of such requests would result in 989 a flood of MDN notifications to the target of the attack. Such an 990 attack could overrun the capacity of the targeted mailbox and deny 991 service. 993 For that reason, MDN's SHOULD NOT be sent automatically where the 994 "disposition-notification-to:" address is different from the envelope 995 MAIL FROM address. See Section 2.1 for further discussion. 997 7. Collected ABNF Grammar 999 NOTE: The following lexical tokens are defined in RFC-MSGFMT [2]: 1000 CRLF, FWS, CFWS, field-name, mailbox, msg-id, text. The following 1001 lexical tokens are defined in RFC-SMTP [1]: atom. (Note that RFC- 1002 MSGFMT [2] also defines "atom", but the version from RFC-SMTP [1] is 1003 more restrictive and this more restrictive version is used in this 1004 document.) The definitions of attribute and value are as in the 1005 definition of the Content-Type header field in RFC-MIME-BODY [3]. 1007 Message header fields: 1009 mdn-request-header = 1010 "Disposition-Notification-To" ":" [FWS] 1011 mailbox *("," [FWS] mailbox) 1012 Disposition-Notification-Options = 1013 "Disposition-Notification-Options" ":" [FWS] 1014 disposition-notification-parameter-list 1015 disposition-notification-parameter-list = 1016 disposition-notification-parameter 1017 *(";" [FWS] disposition-notification-parameter) 1018 disposition-notification-parameter = attribute [FWS] "=" [FWS] 1019 importance [FWS] "," [FWS] value *([FWS] "," [FWS] value) 1020 importance = "required" / "optional" 1021 original-recipient-header = 1022 "Original-Recipient" ":" [FWS] address-type [FWS] ";" [FWS] generic-address 1023 Report content: 1024 disposition-notification-content = 1025 [ reporting-ua-field CRLF ] 1026 [ mdn-gateway-field CRLF ] 1027 [ original-recipient-field CRLF ] 1028 final-recipient-field CRLF 1029 [ original-message-id-field CRLF ] 1030 disposition-field CRLF 1031 *( failure-field CRLF ) 1032 *( error-field CRLF ) 1033 *( extension-field CRLF ) 1034 OWS = *WSP 1035 ; Optional whitespace. 1036 ; MDN generators SHOULD use "*WSP" 1037 ; (typically a single space or nothing). 1038 ; MDN parsers MUST parse it as "[CFWS]". 1039 address-type = atom 1040 mta-name-type = atom 1041 reporting-ua-field = "Reporting-UA" ":" OWS ua-name OWS [ ";" OWS ua-product OWS ] 1042 ua-name = *text-no-semi 1043 ua-product = *(FWS / text) 1044 text-no-semi = %d1-9 / ; "text" characters excluding NUL, CR, 1045 %d11 / %d12 / %d14-58 / %d60-127 ; LF, or semi-colon 1046 mdn-gateway-field = "MDN-Gateway" ":" OWS mta-name-type OWS ";" OWS mta-name 1047 mta-name = *text 1048 original-recipient-field = 1049 "Original-Recipient" ":" OWS address-type OWS ";" OWS generic-address OWS 1050 generic-address = *text 1051 final-recipient-field = 1052 "Final-Recipient" ":" OWS address-type OWS ";" OWS generic-address OWS 1053 original-message-id-field = "Original-Message-ID" ":" OWS msg-id OWS 1054 disposition-field = 1055 "Disposition" ":" OWS disposition-mode OWS ";" 1056 OWS disposition-type 1058 [ OWS "/" OWS disposition-modifier 1059 *( OWS "," OWS disposition-modifier ) ] OWS 1060 disposition-mode = action-mode OWS "/" OWS sending-mode 1061 action-mode = "manual-action" / "automatic-action" 1062 sending-mode = "MDN-sent-manually" / "MDN-sent-automatically" 1063 disposition-type = "displayed" / "deleted" / "dispatched" / 1064 "processed" 1065 disposition-modifier = "error" / disposition-modifier-extension 1066 disposition-modifier-extension = atom 1067 failure-field = "Failure" ":" *(FWS / text) 1068 error-field = "Error" ":" *(FWS / text) 1069 extension-field = extension-field-name ":" *(FWS / text) 1070 extension-field-name = field-name 1072 8. Guidelines for Gatewaying MDNs 1074 NOTE: This section provides non-binding recommendations for the 1075 construction of mail gateways that wish to provide semi-transparent 1076 disposition notifications between the Internet and another electronic 1077 mail system. Specific MDN gateway requirements for a particular pair 1078 of mail systems may be defined by other documents. 1080 8.1. Gatewaying from other mail systems to MDNs 1082 A mail gateway may issue an MDN to convey the contents of a "foreign" 1083 disposition notification over Internet Mail. When there are 1084 appropriate mappings from the foreign notification elements to MDN 1085 fields, the information may be transmitted in those MDN fields. 1086 Additional information (such as might be needed to tunnel the foreign 1087 notification through the Internet) may be defined in extension MDN 1088 fields. (Such fields should be given names that identify the foreign 1089 mail protocol, e.g., X400-* for X.400 protocol elements). 1091 The gateway must attempt to supply reasonable values for the 1092 Reporting-UA, Final-Recipient, and Disposition fields. These will 1093 normally be obtained by translating the values from the foreign 1094 notification into their Internet-style equivalents. However, some 1095 loss of information is to be expected. 1097 The sender-specified recipient address and the original message-id, 1098 if present in the foreign notification, should be preserved in the 1099 Original-Recipient and Original-Message-ID fields. 1101 The gateway should also attempt to preserve the "final" recipient 1102 address from the foreign system. Whenever possible, foreign protocol 1103 elements should be encoded as meaningful printable ASCII strings. 1105 For MDNs produced from foreign disposition notifications, the name of 1106 the gateway MUST appear in the MDN-Gateway field of the MDN. 1108 8.2. Gatewaying from MDNs to other mail systems 1110 It may be possible to gateway MDNs from the Internet into a foreign 1111 mail system. The primary purpose of such gatewaying is to convey 1112 disposition information in a form that is usable by the destination 1113 system. A secondary purpose is to allow "tunneling" of MDNs through 1114 foreign mail systems in case the MDN may be gatewayed back into the 1115 Internet. 1117 In general, the recipient of the MDN (i.e., the sender of the 1118 original message) will want to know, for each recipient: the closest 1119 available approximation to the original recipient address, and the 1120 disposition (displayed, printed, etc.). 1122 If possible, the gateway should attempt to preserve the Original- 1123 Recipient address and Original-Message-ID (if present) in the 1124 resulting foreign disposition report. 1126 If it is possible to tunnel an MDN through the destination 1127 environment, the gateway specification may define a means of 1128 preserving the MDN information in the disposition reports used by 1129 that environment. 1131 8.3. Gatewaying of MDN-requests to other mail systems 1133 By use of the separate disposition-notification-to request header 1134 field, this specification offers a richer functionality than most, if 1135 not all, other email systems. In most other email systems, the 1136 notification recipient is identical to the message sender as 1137 indicated in the "from" address. There are two interesting cases 1138 when gatewaying into such systems: 1140 1. If the address in the disposition-notification-to header field is 1141 identical to the address in the SMTP "MAIL FROM", the expected 1142 behavior will result, even if the disposition-notification-to 1143 information is lost. Systems should propagate the MDN request. 1145 2. If the address in the disposition-notification-to header field is 1146 different from the address in the SMTP "MAIL FROM", gatewaying 1147 into a foreign system without a separate notification address 1148 will result in unintended behavior. This is especially important 1149 when the message arrives via a mailing list expansion software 1150 that may specifically replace the SMTP "MAIL FROM" address with 1151 an alternate address. In such cases, the MDN request should not 1152 be gatewayed and should be silently dropped. This is consistent 1153 with other forms of non-support for MDN. 1155 9. Example 1157 NOTE: This example is provided as illustration only, and is not 1158 considered part of the MDN protocol specification. If the example 1159 conflicts with the protocol definition above, the example is wrong. 1161 Likewise, the use of *-type subfield names or extension fields in 1162 this example is not to be construed as a definition for those type 1163 names or extension fields. 1165 This is an MDN issued after a message has been displayed to the user 1166 of an Internet Mail user agent. 1168 Date: Wed, 20 Sep 1995 00:19:00 (EDT) -0400 1169 From: Joe Recipient 1170 Message-Id: <199509200019.12345@example.com> 1171 Subject: Disposition notification 1172 To: Jane Sender 1173 MIME-Version: 1.0 1174 Content-Type: multipart/report; report-type=disposition-notification; 1175 boundary="RAA14128.773615765/example.com" 1177 --RAA14128.773615765/example.com 1179 The message sent on 1995 Sep 19 at 13:30:00 (EDT) -0400 to Joe 1180 Recipient with subject "First draft of 1181 report" has been displayed. 1182 This is no guarantee that the message has been read or understood. 1184 --RAA14128.773615765/example.com 1185 content-type: message/disposition-notification 1187 Reporting-UA: joes-pc.cs.example.com; Foomail 97.1 1188 Original-Recipient: rfc822;Joe_Recipient@example.com 1189 Final-Recipient: rfc822;Joe_Recipient@example.com 1190 Original-Message-ID: <199509192301.23456@example.org> 1191 Disposition: manual-action/MDN-sent-manually; displayed 1193 --RAA14128.773615765/example.com 1194 content-type: message/rfc822 1196 [original message optionally goes here] 1198 --RAA14128.773615765/example.com-- 1200 10. IANA Considerations 1202 This document specifies three types of parameters that must be 1203 registered with the Internet Assigned Numbers Authority (IANA). 1205 The forms below are for use when registering a new disposition- 1206 notification-parameter name for the Disposition-Notification-Options 1207 header field, a new disposition modifier name, or a new MDN extension 1208 field. Each piece of information required by a registration form may 1209 be satisfied either by providing the information on the form itself, 1210 or by including a reference to a published, publicly available 1211 specification that includes the necessary information. IANA MAY 1212 reject registrations because of incomplete registration forms or 1213 incomplete specifications. 1215 To register, complete the following applicable form and send it via 1216 electronic mail to . 1218 10.1. Disposition-Notification-Options header field disposition- 1219 notification-parameter names 1221 A registration for a Disposition-Notification-Options header field 1222 disposition-notification-parameter name MUST include the following 1223 information: 1225 a. The proposed disposition-notification-parameter name. 1227 b. The syntax for disposition-notification-parameter values, 1228 specified using BNF, ABNF, regular expressions, or other non- 1229 ambiguous language. 1231 c. If disposition-notification-parameter values are not composed 1232 entirely of graphic characters from the US-ASCII repertoire, a 1233 specification for how they are to be encoded as graphic US-ASCII 1234 characters in a Disposition-Notification-Options header field. 1236 d. A reference to a standards track RFC or experimental RFC approved 1237 by the IESG that describes the semantics of the disposition- 1238 notification-parameter values. 1240 10.2. Disposition modifier names 1242 A registration for a disposition-modifier name (used in the 1243 Disposition field of a message/disposition-notification) MUST include 1244 the following information: 1246 a. The proposed disposition-modifier name. 1248 b. A reference to a standards track RFC or experimental RFC approved 1249 by the IESG that describes the semantics of the disposition 1250 modifier. 1252 10.3. MDN extension field names 1254 A registration for an MDN extension-field name MUST include the 1255 following information: 1257 a. The proposed extension field name. 1259 b. The syntax for extension values, specified using BNF, ABNF, 1260 regular expressions, or other non-ambiguous language. 1262 c. If extension-field values are not composed entirely of graphic 1263 characters from the US-ASCII repertoire, a specification for how 1264 they are to be encoded as graphic US-ASCII characters in a 1265 Disposition-Notification-Options header field. 1267 d. A reference to a standards track RFC or experimental RFC approved 1268 by the IESG that describes the semantics of the extension field. 1270 11. Acknowledgements 1272 The contributions of Bruce Lilly and Alfred Hoenes are gratefully 1273 acknowledged for this revision. 1275 The contributions of Roger Fajman and Greg Vaudreuil to earlier 1276 versions of this document are also gratefully acknowledged. 1278 12. References 1280 12.1. Normative References 1282 [1] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, 1283 October 2008. 1285 [2] Resnick, P., Ed., "Internet Message Format", RFC 5322, 1286 October 2008. 1288 [3] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 1289 Extensions (MIME) Part One: Format of Internet Message 1290 Bodies", RFC 2045, November 1996. 1292 [4] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 1293 Extensions (MIME) Part Two: Media Types", RFC 2046, 1294 November 1996. 1296 [5] Moore, K., "MIME (Multipurpose Internet Mail Extensions) 1297 Part Three: Message Header Extensions for Non-ASCII Text", 1298 RFC 2047, November 1996. 1300 [6] Vaudreuil, G., "The Multipart/Report Content Type for the 1301 Reporting of Mail System Administrative Messages", RFC 1302 3462, January 2003. 1304 [7] Moore, K., "Simple Mail Transfer Protocol (SMTP) Service 1305 Extension for Delivery Status Notifications (DSNs)", RFC 1306 3461, January 2003. 1308 [8] Moore, K. and G. Vaudreuil, "An Extensible Message Format 1309 for Delivery Status Notifications", RFC 3464, January 1310 2003. 1312 [9] Bradner, S., "Key words for use in RFCs to Indicate 1313 Requirement Levels", BCP 14, RFC 2119, March 1997. 1315 [10] Melnikov, A., "Message Disposition Notification (MDN) 1316 profile for Internet Message Access Protocol (IMAP)", RFC 1317 3503, March 2003. 1319 12.2. Informative References 1321 [11] Hoffman, P., "Enhanced Security Services for S/MIME", RFC 1322 2634, June 1999. 1324 [12] Murchison, K., "Sieve Email Filtering: Subaddress 1325 Extension", RFC 5233, January 2008. 1327 [13] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 1328 4rev1", RFC 3501, March 2003. 1330 Appendix A. Changes from RFC 3798 1332 The values of "dispatched" and "processed" were lost from the ABNF 1333 for "disposition-type". 1335 Because the warning disposition modifier was previously removed, 1336 warning-field has also been removed. 1338 The ABNF for ua-name and ua-product included semi-colon, which could 1339 not be distinguished from *text in the production. The ua-name and 1340 ua-product definitions were restricted to not include semi-colon. 1342 The ABNF did not indicate all places that whitespace was allowable, 1343 in particular folding whitespace, although all implementations allow 1344 whitespace and folding in the header fields just like any other 1345 RFC5322 [2]-formatted header field. There were also a number of 1346 places in the ABNF that inconsistently permitted comments and 1347 whitespace in one leg of the production and not another. The ABNF 1348 now specifies FWS and CFWS in several places that should have already 1349 been specified by the grammar. 1351 Extension-field was defined in the collected grammar but not in the 1352 main text. 1354 [[CREF4: Shouldn't the places we use *text and *text-no-semi allow 1355 FWS? ]] 1357 The comparison of mailboxes in Disposition-Notification-To to the 1358 Return-Path addr-spec was clarified. 1360 The use of the grammar production "parameter" was confusing with the 1361 RFC2045 [3] production of the same name, as well as other uses of the 1362 same term. These have been clarified. 1363 [[CREF5: Not sure what to do with this one: (From Bruce) In the case 1364 of the message header fields, RFC 2822 also specifies minimum and 1365 maximum counts for each header field, and similar guidance would 1366 clarify 3798 (e.g. are multiple Disposition-Notification-Options 1367 fields permitted in a single message header, and if so, what 1368 semantics apply?). ]] 1369 [[CREF6: Not sure what to do with this one: (From Bruce) Note also 1370 that RFC 2045 is itself based on RFC 822 rather than 2822, so the 1371 issue of where CFWS is permitted or prohibited should probably be 1372 clearly specified where "attribute" and "value" are used. Note 1373 further that the RFC 2045 definitions are clarified by errata and 1374 modified by RFC 2231, and by RFC 2231 errata. Finally, note that RFC 1375 2231 has provisions for continuation of long parameter values (where 1376 there would otherwise be problems with the maximum line length 1377 specifications of RFCs 822 and 2822), specification of language and 1378 charset, and provision for compatible handling of non-ASCII text, 1379 none of which are provided for in the RFC 3798 disposition- 1380 notification parameters. It might be a good idea to think about that 1381 now, as a future change would almost certainly reset the document 1382 status to "Proposed". ]] 1384 A clarification was added on the extent of the 7bit nature of MDNs. 1386 Uses of the terms "may" and "might" were clarified. 1388 A clarification was added on the order of the fields in the message/ 1389 disposition-notification content. 1390 [[CREF7: Not sure what to do with this one: (From Bruce) 3.1.1 1391 explicitly mentions use of RFC 2047 encoded-words in comments 1392 (however, as noted above there is no explicit provision for 1393 comments), but fails to mention the other contexts in which encoded- 1394 words may be used, viz. in an RFC [2]822 "phrase" (e.g. in the 1395 display name of a name-addr mailbox in Disposition-Notification-To 1396 (therefore, the discussion of encoded-words should probably be moved 1397 earlier in the document, prior to the specification of Disposition- 1398 Notification-To]), and in unstructured text (i.e. every instance of 1399 *text in the ABNF). In particular, use of encoded-words might be 1400 highly desirable in the following places: *) the ua-product portion 1401 of the Reporting-UA field; *) the generic-address part of the 1402 Original-Recipient and Final-Recipient fields; *) the (unstructured) 1403 field bodies of Error, Failure, and Warning fields; in structured 1404 extension fields where the context (per RFC 2047) is appropriate in 1405 unstructured extension fields; *) in X- extension fields (see RFC 1406 2047 for related X- message header fields). In cases where the field 1407 syntax is shared with DSN fields, some coordination with the RFC 346x 1408 authors might be desirable. ]] 1410 Authors' Addresses 1412 Tony Hansen (editor) 1413 AT&T Laboratories 1414 200 Laurel Ave. South 1415 Middletown, NJ 07748 1416 USA 1418 Email: tony+rfc3798@maillennium.att.com 1419 Alexey Melnikov (editor) 1420 Isode Ltd 1421 14 Castle Mews 1422 Hampton, Middlesex TW12 2NP 1423 UK 1425 Email: Alexey.Melnikov@isode.com