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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Fax Working Group Larry Masinter 2 Internet Draft Xerox Corporation 3 September 17, 1998 Dan Wing 4 Expires January 1999 Cisco Systems 5 draft-ietf-fax-eifax-04.txt 7 Extended Facsimile Using Internet Mail 9 Status of this memo 11 This document is an Internet-Draft. Internet-Drafts are working 12 documents of the Internet Engineering Task Force (IETF), its areas, 13 and its working groups. Note that other groups may also distribute 14 working documents as Internet-Drafts. 16 Internet-Drafts are draft documents valid for a maximum of six months 17 and may be updated, replaced, or obsoleted by other documents at any 18 time. It is inappropriate to use Internet-Drafts as reference 19 material or to cite them other than as "work in progress." 21 To view the entire list of current Internet-Drafts, please check 22 the "1id-abstracts.txt" listing contained in the Internet-Drafts 23 Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net 24 (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au 25 (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu 26 (US West Coast). 28 This draft is a product of the IETF FAX working group. To subscribe 29 to the mailing list, send a message to ietf-fax-request@imc.org with 30 the line "subscribe" in the body of the message. Archives are 31 available from http://www.imc.org/ietf-fax. 33 Copyright Notice 35 Copyright (C) The Internet Society (1998). All Rights Reserved. 37 Abstract 39 This document describes extensions to 'Simple Mode of Facsimile Using 40 Internet Mail' [RFC2305] to provide additional features, including 41 transmission of enhanced document characteristics (higher resolution, 42 color) and confirmation of delivery and processing. 44 These additional features are designed to provide the highest level 45 of interoperability with the existing and future standards-compliant 46 email infrastructure and mail user agents, while providing a level of 47 service that approximates the level currently enjoyed by fax users. 49 1. Introduction 51 This document notes a number of enhancements to the "Simple Mode of 52 Facsimile Using Internet Mail" [RFC2305] that may be combined to 53 create an extended mode of facsimile using Internet mail. 55 The new features are designed to be interoperable with the existing 56 base of mail transfer agents (MTAs) and mail user agents (MUAs), 57 and take advantage of existing standards for advanced functionality 58 such as positive delivery confirmation and disposition notification. 59 The enhancements described in this document utilize the messaging 60 infrastructure, where possible, instead of creating fax-specific 61 features which are unlikely to be implemented in non-fax messaging 62 software. 64 This document describes a protocol suite that satisfies all of the 65 required and highly desirable features identified in [GOALS]: 67 * Delivery confirmation (Section 2) (required) 68 * Additional document features (Section 3) (optional) 70 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 71 "SHOULD", SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 72 document are to be interpreted as described in [RFC2119]. 74 1.1. Definition of terms 76 The term 'processing' indicates the ability to successfully render or 77 successfully transmit the contents of the message to a printer, on a 78 display device, or to a fax machine. 80 The term 'recipient' indicates the device which processes the content 81 of the mail message and renders it to the user by transmitting it to 82 a remote fax machine, printer, displaying it on a terminal. For 83 example, a recipient could be implemented as a traditional Mail User 84 Agent on a PC, a standalone device which retreives mail using POP3 or 85 IMAP, an SMTP server which prints incoming messages (similar to an 86 LPR server). 88 1.2. GSTN Fax Gateways ("onramp"/"offramp") 90 The behavior of gateways from GSTN fax to SMTP ("onramps") and from 91 SMTP to GSTN fax ("offramps") are not described in this document. 92 However, such gateways SHOULD have the behavior characteristics of 93 senders and recipients as described in this document. 95 2. Delivery and Processing Confirmation 96 In traditional GSTN-based realtime facsimile, the receiving terminal 97 acknowledges successful receipt and processing of every page [T.30]. 99 In Internet Mail, the operations of Delivery (to the mailbox) and 100 Disposition (to paper or a screen) may be separated in time (due to 101 store and forwarding of messages) and location (due to separation of 102 delivery agent (MTA) and user agent (MUA)). The confirmation of 103 these two operations are supplied by two different standards-track 104 documents: Delivery Status Notifications (DSN) [RFC1891, RFC1894] 105 and Message Disposition Notifications (MDN) [RFC2298], respectively. 107 This section defines requirements for devices or services that are to 108 be considered compliant with the delivery and processing confirmation 109 section of this memo. 111 2.1. Sender Requirements 113 The envelope-from address provided by the sender MUST be able to 114 receive all types of Delivery Status Notifications [RFC1894] and be 115 able to receive delivery failure or delayed delivery messages that 116 are not in the Delivery Status Notification format [RFC1894]. Note 117 that a DSN or delivery failure message may be sent to the 118 envelope-from address even if the sender doesn't request a DSN. 120 2.1.1. Delivery Confirmation 122 Following the terminology of [SUBMIT], a sender MUST use a mail 123 submission server (which may be resident on the same device as the 124 sender). To request delivery confirmation, the sender MUST request 125 Delivery Status Notification by including the the esmtp-value SUCCESS 126 with the esmtp-keyword NOTIFY using the method described in section 127 5.1 of [RFC1891]. 129 2.1.2. Processing Confirmation 131 To request processing confirmation, the sender MUST 132 request Message Disposition Notification using the method 133 described in section 2 of [RFC2298]. 135 Because a recipient can always silently ignore a request 136 for an MDN [section 2.1 of RFC2298]: 137 * MDNs MUST NOT be used for delivery confirmation, but are only 138 useful for disposition ("processing") notification. 139 * the sender MUST NOT assume the recipient will respond to an MDN 140 request in a subsequent message, even if the recipient has 141 always responded to MDNs in the past. 143 The address provided by the sender on the Disposition-Notification-To 144 field MUST be able to receive Message Disposition Notifications 145 messages [RFC2298] and be able to receive messages that are not in 146 the Message Disposition Notification format (due to the existence of 147 legacy systems that generate non-RFC2298-compliant responses to the 148 Disposition-Notification-To field). 150 2.2. Recipient Requirements 152 Recipients in compliance with this document SHOULD implement MDN 153 [RFC2298], and SHOULD implement Offramp Gateway Extensions for DSN 154 and MDN [REPORT-EXTENSIONS]. 156 If the recipient is an SMTP server, it behaves as part of the 157 receiver infrastructure and is therefore subject to the "Receiver 158 Infrastructure" requirements of this document. 160 See also "Recipient Recommendations" in section 5. 162 2.2.1. MDN Recipient Requirements 164 Recipients MUST be configurable to silently ignore a request for an 165 MDN ([section 2.1 of RFC2298]). 167 If the recipient is an automated message processing system which is 168 not associated with a person, the device MAY be configurable to 169 always respond to MDN requests, but in all cases MUST be configurable 170 to never generate MDNs. 172 A recipient MUST NOT generate an unsolicited MDN to indicate 173 successful processing, but a recipient MAY generate an unsolicited 174 MDN (sent to the envelope-from (Return-Path:) address) to indicate 175 processing failure following the rules in the above paragraph. 177 2.2.3. Recipients using Mailbox Access Protocols 179 A recipient using [POP3] or [IMAP4] to retrieve its mail is not 180 allowed to generate a Delivery Status Notification message [RFC1894]. 182 The recipient MUST NOT use anything but the POP/IMAP username to map 183 to a single destination. For example, using any RFC822 field or 184 information within the message body or MIME parts to make a decision 185 about the destination is not permitted. 187 2.3. Messaging Infrastructure Requirements 189 This section explains the requirements of the SMTP messaging 190 infrastructure used by the sender and receiver. This infrastructure 191 is commonly provided by the ISP or a company's internal mailers but 192 can actually be provided by another organization with appropriate 193 service contracts. 195 2.3.1. Sender Infrastructure 197 Support for DSN [RFC1891] MUST be provided by the mail submission 198 server [SUBMIT] used by the sender, and MUST be provided up to 199 the mailer responsible for communicating with external (Internet) 200 mailers. 202 2.3.2. Receiver Infrastructure 204 Support for DSN [RFC1891] MUST be provided by the external 205 (Internet-accessible) mailer, and MUST be provided by each mailer 206 between the external mailer and the recipient. If the recipient is 207 implemented as an SMTP server it MUST also support DSN [RFC1891]. 209 3. Additional document capabilities 211 Section 4 of [RFC2305] only allows sending the minimum subset 212 of TIFF for Facsimile "unless the sender has prior knowledge 213 of other TIFF fields or values supported by the recipient." 215 A recipient SHOULD indicate which features and values from among 216 those available in [FAX-SCHEMA] are supported using one of the 217 mechanisms defined below. 219 Three methods for the sender to acquire such knowledge are 220 permitted: 222 1. Sender manual configuration 223 2. Capabilities in Directory 224 3. Capabilities returned in MDN or DSN 226 In any implementation it possible for a locally-stored 227 cache of capabilities to lose synchronization with the 228 recipient's actual capabilities. A mechanism should be 229 provided to allow the sender to override the locally-stored 230 cache of capabilities. Also note section 4.1 of this 231 document. 233 3.1. Sender manual configuration 235 One way a sender can send a document which exceeds the minimum 236 subset allowed by [RFC2305] is for the user controlling the sender 237 to manually override the default settings, usually on a 238 per-recipient basis. For example, during transmission a 239 user could indicate the recipient is capable of receiving 240 high resolution images or color images. 242 While awkward and not automatic, this mechanism reflects the current 243 state of deployment of configuration for extended capabilities to 244 ordinary Internet email users. 246 3.2. Capabilities in Directory 248 A future direction for enhanced document features is to create a 249 directory structure of recipient capabilities, deployed, for example, 250 through LDAP or DNS. The directory would provide a mechanism by which 251 a sender could determine a recipient's capabilities before message 252 construction or transmission, using a directory lookup. Such 253 mechanisms are not defined in this document. 255 There is active investigation within the IETF to develop a solution 256 to this problem, which would resolve a wide range of issues with 257 store-and-forward messaging. 259 3.3. Capabilities Returned in MDN or DSN 261 As outlined in section 2 of this document, a sender may request a 262 positive DSN or an MDN. 264 If the recipient implements [REPORTING-EXTENSIONS], the 265 DSN or MDN that is returned can contain information describing 266 the recipient's capabilities. The sender can use this information 267 for subsequent communications with that recipient. 269 The advantage of this approach is that additional infrastructure is 270 not required (unlike section 3.2), and the information is acquired 271 automatically (unlike section 3.1). 273 4. Security Considerations 275 As this document is an extension of [RFC2305], the Security 276 Considerations section of [RFC2305] applies to this document. 278 The following additional security considerations are introduced by 279 the new features described in this document. 281 4.1. Inaccurate Capabilities Information 283 Inaccurate capability information (section 3) could cause a denial 284 of service. The capability information could be inaccurate due to 285 many reasons, including compromised or improperly configured 286 directory server, improper manual configuration of sender, 287 compromised DNS, or spoofed MDN. If a sender is using cached 288 capability information, it SHOULD be manually confirmed by a user 289 before it is automatically used. 291 4.2. Forged MDNs or DSNs 293 Forged DSNs or MDNs, as described in [RFC1892, RFC1894, RFC2298] 294 can provide incorrect information to a sender. 296 5. Implementation Notes 298 This section contains notes to implementors. 300 5.1. Submit mailer does not support DSN 302 In some installations the generally available submit server may not 303 support DSNs. In such circumstances, it may be useful for the sender 304 to implement [RFC974] mail routing as well as additional submission 305 server functions [SUBMIT] so that the installation is not constrained 306 by limitations of the incumbent submission server. 308 5.2. Recipient Recommendations 310 To provide a high degree of reliability, it is desirable for 311 the sender to know that a recipient could not process a message. 312 The inability to successfully process a message may be detectable 313 by the recipient's MTA or MUA. 315 If the recipient's MTA determines the message cannot be processed, 316 the recipient's MTA is strongly encouraged to reject the message with 317 a [RFC1893] status code of 5.6.--???????--. This status code may be 318 returned in response to the end-of-mail-data indicator if the MTA 319 supports [RFC2034], or after message reception by generating a 320 delivery failure DSN ("bounce"). 322 Note: Because DSN bounces are not requested by the sender and are 323 not 'approved' by the receiver, DSNs can provide a more robust 324 mechanism than performing this function in the MUA using MDNs. 326 If the message contains an MDN request and the recipient's MUA 327 determines the message cannot be processed, the recipient's MUA is 328 strongly encouraged to repond to an MDN request and indicate that 329 processing failed with the disposition-type "processed" or 330 "displayed" and disposition-modifier "error" or "warning" [RFC2298]. 332 6. Acknowledgements 334 The authors would like to acknowledge the members of the IETF 335 Internet Fax working group, and especially the following contributors 336 who provided assistance and input during the development of this 337 document: Vivian Cancio, Richard Coles, David Crocker, Ned Freed, 338 Graham Klyne, MAEDA Toru, Geoff Marshall, Keith Moore, George Pajari, 339 James Rafferty, Mike Ruhl, Richard Shockey, Brian Stafford. 341 7. References 343 [GOALS] L. Masinter, "Terminology and Goals for Internet Fax", 344 Internet Draft, Work in Progress, draft-ietf-fax-goals-XX.txt. 346 [REPORT-EXTENSIONS] D. Wing, "Offramp Gateway Extensions to DSN and 347 MDN". Internet Draft, Work in Progress, 348 draft-ietf-fax-report-extensions.txt. 350 [RFC1891] K. Moore, "SMTP Service Extensions for Delivery Status 351 Notifications", RFC 1891, January 1996. 353 [RFC1894] K. Moore, G. Vaudreuil, "An Extensible Message Format for 354 Delivery Status Notifications", RFC 1894, January 1996. 356 [RFC2034] N. Freed, "SMTP Service Extension for Returning Enhanced 357 Error Codes", RFC 2034, October 1996. 359 [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate 360 Requirement Levels", RFC 2119, March 1997. 362 [RFC2298] R. Fajman, "An Extensible Message Format for Message 363 Disposition Notifications", RFC 2298, March 1998. 365 [RFC2305] K. Toyoda, H. Ohno, J. Murai, D. Wing, "A Simple Mode of 366 Facsimile Using Internet Mail", RFC 2305, March 1998. 368 [RFC974] C. Partridge. "Mail routing and the domain system", RFC 974, 369 January 1986. 371 [SCHEMA] Internet Draft, Work in Progress. 373 [SUBMIT] R. Gellens, J. Klensin, "Message Submission", Internet 374 Draft, Work in Progress, draft-gellens-submit-XX.txt. 376 8. Authors' Addresses 378 Larry Masinter 379 Xerox Palo Alto Research Center 380 3333 Coyote Hill Road 381 Palo Alto, CA 94304 USA 383 Fax: +1 415 812 4333 384 EMail: masinter@parc.xerox.com 386 Dan Wing 387 Cisco Systems, Inc. 388 101 Cooper Street 389 Santa Cruz, CA 95060 USA 391 Phone: +1 831 457 5200 392 Fax: +1 831 457 5208 393 EMail: dwing@cisco.com 395 9. Copyright 397 Copyright (C) The Internet Society 1998. All Rights Reserved. 399 This document and translations of it may be copied and furnished to 400 others, and derivative works that comment on or otherwise explain it 401 or assist in its implementation may be prepared, copied, published 402 and distributed, in whole or in part, without restriction of any 403 kind, provided that the above copyright notice and this paragraph are 404 included on all such copies and derivative works. However, this 405 document itself may not be modified in any way, such as by removing 406 the copyright notice or references to the Internet Society or other 407 Internet organizations, except as needed for the purpose of 408 developing Internet standards in which case the procedures for 409 copyrights defined in the Internet Standards process must be 410 followed, or as required to translate it into languages other than 411 English. 413 The limited permissions granted above are perpetual and will not be 414 revoked by the Internet Society or its successors or assigns. 416 This document and the information contained herein is provided on an 417 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 418 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 419 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 420 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 421 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.