Network Working Group E. Burger Internet Draft SnowShore Networks Document: draft-ietf-vpim-cc-07.txt Category: Standards Track Updates: RFC 3204 Expires December 2002 June 1, 2002 Critical Content MIME Parameter Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026 [1]. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, and other documents may obsolete this one at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." One can access the list of current Internet-Drafts at http://www.ietf.org/ietf/1id-abstracts.txt One can access the list of Internet-Draft Shadow Directories at http://www.ietf.org/shadow.html. This document is a work product of the IETF Voice Profile for Internet Mail (VPIM) Work Group. 1. Abstract This document describes the use of a mechanism for identifying body parts that a sender deems critical in a multi-part Internet mail message. The mechanism described is a parameter to Content- Disposition, as described by RFC 3204. By knowing what parts of a message the sender deems critical, a content gateway can intelligently handle multi-part messages when providing gateway services to systems of lesser capability. Critical content can help a content gateway to decide what parts to forward. It can indicate how hard a gateway should try to deliver a body part. It can help the gateway to pick body parts that are safe to silently delete when a system of lesser capability receives a message. In addition, critical content can help the gateway chose the notification strategy for the receiving system. Likewise, if the sender expects the destination to do some processing on a body part, critical content allows the sender to mark body parts that the receiver must process. Expires December 2002 [Page 1]
Critical Content of Internet Mail June 2002 Table of Contents 1. Abstract...........................................................1 2. Conventions used in this document..................................2 3. Introduction.......................................................3 4. Handling Parameter.................................................3 4.1. REQUIRED.........................................................4 4.2. OPTIONAL.........................................................4 4.3. Default Values...................................................4 4.4. Other Values.....................................................5 5. Collected Syntax...................................................5 6. Notification.......................................................5 6.1. DSN vs. MDN Generation...........................................6 6.2. Summary..........................................................6 7. Status Code........................................................7 8. Requirements for Critical Content..................................8 8.1. Needs............................................................8 8.2. Current Approaches...............................................9 9. The Content Gateway...............................................10 9.1. Integrated Content Gateway......................................10 9.2. Disaggregated Delivery Network..................................11 10. Backward Compatibility Considerations............................11 11. MIME Interactions................................................11 11.1. multipart/alternative..........................................11 11.2. multipart/related..............................................12 11.3. message/rfc822.................................................12 12. Implementation Examples..........................................12 12.1. Content Gateways...............................................12 12.2. Disaggregated Content Gateway..................................13 13. Security Considerations..........................................14 14. IANA Considerations..............................................14 15. References.......................................................15 16. Acknowledgments..................................................16 17. Author's Address.................................................16 2. Conventions used in this document This document refers generically to the sender of a message in the masculine (he/him/his) and the recipient of the message in the feminine (she/her/hers). This convention is purely for convenience and makes no assumption about the gender of a message sender or recipient. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [2]. Burger Expires December 2002 [Page 2]
Critical Content of Internet Mail June 2002 NOTE: Notes, such as this one, provide additional nonessential information that the reader may skip without missing anything essential. The primary purpose of these non-essential notes is to convey information about the rationale of this document, or to place this document in the proper historical or evolutionary context. Readers whose sole purpose is to construct a conformant implementation may skip such information. However, it may be of use to those who wish to understand why we made certain design choices. 3. Introduction The specification of Critical Content is small and compact. For the benefit of developers, the specification comes first, the rationale after. One concept that an implementer must understand is the content gateway. Section 9 describes the content gateway. In brief, a content gateway has knowledge of the receiving system's capabilities. The content gateway passes messages the receiving system can process, render or store. The content gateway can modify a message, for example by deleting unrenderable or storable body parts, for delivery to the receiving system. Finally, the content gateway can reject a message that the receiving system cannot handle. In this document, the "sending agent" is the originator of the message. It could be a mail user agent (MUA) for an Internet message, or a SIP User Agent Client (UAC) for a SIP [3] message. NOTE: This document updates RFC 3204 to separate the Handling parameter from the ISUP/QSIG transport mechanism. The protocol described here is identical in functionality to RFC 3204 with respect to SIP. Future versions of RFC 3204 should reference this document for the Handling parameter, as it is orthogonal to the tunneling of signaling. 4. Handling Parameter The Handling parameter is a Content-Disposition [5] parameter inserted by the sending agent to indicate to the content gateway whether to consider the marked body part critical. A REQUIRED body part is one the sender requires the receiving system to deliver for him to consider the message delivered. An OPTIONAL body part is one the sender doesn't care whether the receiving system delivers it or not. A content gateway can silently Burger Expires December 2002 [Page 3]
Critical Content of Internet Mail June 2002 delete such body parts if the receiving system cannot deliver the part. The terms "entity" and "body part" have the meanings defined in [5]. 4.1. REQUIRED "Handling=REQUIRED" signifies that this body part is critical to the sender. If the content gateway cannot pass a body part marked REQUIRED, then the entire message has failed. In this case, the content gateway MUST take the appropriate failure action. NOTE: We say "appropriate action", because the sender may have suppressed all notifications. In this case, the appropriate action is to silently discard the message. In addition, as a general MIME parameter, the MIME body part may not be in an Internet Mail message. Moreover, in the SIP case, the appropriate notification is a status return code, not a delivery notification. 4.2. OPTIONAL "Handling=OPTIONAL" signifies that the sender does not care about notification reports for this body part. If the content gateway cannot pass a body part marked OPTIONAL, the receiving system may silently delete the body part. The receiving system MUST NOT return a delivery failure, unless parts marked REQUIRED have also failed. 4.3. Default Values The default value for Handling for a given body part is REQUIRED. This enables the existing notification mechanisms to work for sending agents that do not know about the content notification entity. All body parts are critical, because they have the default marking of REQUIRED. NOTE: In the case of Internet mail, critical content processing is a function of the content gateway and not the mail transfer agent (MTA) or user agent (UA). Often, the entity performing content gateway processing is the receiving UA. However, in this case the UA is acting as a content gateway. Thus the default action for any Content-Disposition [5]-compliant user agent to ignore unrecognized disposition parameters ensures that this mechanism is compatible with the Internet architecture. NOTE: This parameter is fully backwards compatible and works as expected for Internet mail and SIP. Burger Expires December 2002 [Page 4]
Critical Content of Internet Mail June 2002 NOTE: Some VPIMv2 implementations can receive arbitrary e-mail from the Internet. However, these systems are really acting in the capacity of an Internet Voice Mail system. In this case, one would expect the implementation to provide Internet Voice Mail semantics to Internet Voice Mail messages. 4.4. Other Values The content gateway MUST treat unrecognized values as REQUIRED. This is to provide backward compatibility with future uses of the Content-Criticality entity. NOTE: A possible new value is IMPORTANT. An IMPORTANT body part is something the sender wants the receiver to get, but would not want the message rejected outright if the IMPORTANT body part fails, but they do want notification of the failure. However, as no implementations do IMPORTANT, it is not important to this version of this document. 5. Collected Syntax The format of the collected syntax is in accordance with the ABNF of [6]. Note that per RFC 2183 [5], the HANDLING Content-Disposition parameter is not case sensitive. In addition, the notification-type is not case sensitive. "handling" "=" notification-type CRLF notification-type = "REQUIRED" / "OPTIONAL" / other-handling / generic-param other-handling = token 6. Notification One obvious application of critical content is generating a (non-)delivery notification in the Internet mail environment. If the value of the field is OPTIONAL, the content gateway MUST NOT generate a notification. If the value of the field is REQUIRED, the content gateway MAY generate a notification, based on the normal notification request mechanisms. Normal notification request mechanisms include the SMTP RCPT NOTIFY command [7] and the Disposition-Notification-To header [8]. In SIP, all requests have responses. These responses provide notification in the status code of the response. For the RFC 3204 case, a content gateway generates a 415 (Unsupported Media Type) response if the field is REQURED. Burger Expires December 2002 [Page 5]
Critical Content of Internet Mail June 2002 If the sending system requests a notification, and a REQUIRED part fails, the content gateway will generate a notification for the whole message. Conversely, if the gateway cannot pass on a body part marked OPTIONAL, the gateway will not generate a notification. NOTE: This implies that the content gateway must examine the entire message to determine whether it needs to generate a notification. However, the content gateway need not examine the message if it knows it can store and forward all media types. Said differently, Internet e-mail MTAs or gateways can, by default, handle any arbitrary MIME-encapsulated type. Some voice mail systems, on the other hand, cannot store binary attachments at all, such as application/ms-word. The voice mail content gateway, in this example, would be scanning for non-renderable body parts in any event. 6.1. DSN vs. MDN Generation The content gateway generates a delivery status notification (DSN) [8] if it operates as a gateway. The content gateway generates a Message Disposition Notification (MDN) [9] if it operates as a mail user agent. Section 7 describes the operating modes of a content gateway. In short, if there is a MTA that "delivers" the message to the content gateway for processing, the MTA takes responsibility for DSN processing. In this case, the only option available to the content gateway is to generate MDNs. If the content gateway operates as a MTA, then it generates DSNs. DSN generation is the preferred option. If the content gateway is part of a SIP endpoint, then it generates the appropriate success or error response code. 6.2. Summary The following table summarizes the actions expected of a conforming content gateway. NOTE: This section is normative: it suggests what to put into the DSN or MDN. NOTE: In the case of SIP, this section is informative. See RFC 3204 for the normative set of actions on failure. Burger Expires December 2002 [Page 6]
Critical Content of Internet Mail June 2002 +--------------------------------------+ | Sending UA Has Marked Body Part | |---------------------+----------------| | REQUIRED | OPTIONAL | +--------------------+---------------------+----------------+ | Body Part is | | | | Deliverable | Appropriate Action | ignore | +--------------------+---------------------+----------------+ | Body Part is | | | | Undeliverable | Fail Entire Message | ignore | +--------------------+--------------------------------------+ The "Appropriate Action" is the action the content gateway would take given the context of execution. For example, if a sender requests return receipt and the receiver reads a HANDLING body part, the receiving UA must generate the appropriate MDN (following the rules for MDN). Likewise, if the content gateway cannot deliver the body part and the body part is critical, the content gateway generates the appropriate DSN or MDN. "Optional" means the content gateway ignores the disposition of the body part. The content gateway treats the message as if the body part was not present in the message. 7. Status Code The critical content indication, in itself, does not guarantee any notification. Notification follows the rules described in [3], [7], and [8]. NOTE: The content of actual DSNs or MDNs are beyond the scope of this document. This document only specifies how to mark a critical body part. On the other hand, we do envision sensible DSN and MDN contents. For example, DSNs should include the appropriate failure code as enumerated in [10]. Likewise, MDNs should include the failure code in the MDN "Failure:" field. If the receiving system is to generate a notification based on its inability to render or store the media type, the notification should use the status code 5.6.1, "Media not supported", from [9]. For the SIP case, all requests have notification provided by the status response message. Per RFC 3204, a content gateway generates a 415 (Unsupported Media Type) response. Burger Expires December 2002 [Page 7]
Critical Content of Internet Mail June 2002 8. Requirements for Critical Content 8.1. Needs The need for a critical content identification mechanism comes about because of the internetworking of Internet mail systems with messaging systems that do not fulfill all of the semantics of Internet mail. Such legacy systems have a limited ability to render or store all parts of a given message. This document will use the case of an Internet mail system exchanging electronic messages with a legacy voice messaging system for illustrative purposes. Electronic mail has historically been text-centric. Extensions such as MIME [11] enable the user agents to send and receive multi-part, multimedia messages. Popular multimedia data types include binary word processing documents, binary business presentation graphics, voice, and video. Voice mail has historically been audio-centric. Many voice- messaging systems only render voice. Extensions such as fax enable the voice mail system to send and receive fax images as well as create multi-part voice and fax messages. A few voice mail systems can render text using text-to-speech or text-to-fax technology. Although theoretically possible, none can today render video. An important aspect of the interchange between voice messaging services and desktop e-mail client applications is that the rendering capability of the voice-messaging platform is often much less than the rendering capability of a desktop e-mail client. In the e-mail case, the sender has the expectation that the recipient receives all components of a multimedia message. This is so even if the recipient cannot render all body parts. In most cases, the recipient can either find the appropriate rendering tool or tell the sender that she cannot read the particular attachment. This is an important issue. By definition, a MIME-enabled user agent, conforming to [12], will present or make available all of the body parts to the recipient. However, a voice mail system may not be capable of storing non-voice objects. Moreover, the voice mail system may not be capable of notifying the recipient that there were undeliverable message parts. The inability of the receiving system to render a body part is usually a permanent failure. Retransmission of the message will not improve the likelihood of a future successful delivery. Contrast this with the case with normal data delivery. Traditional message failures, such as a garbled message or disabled link will benefit from retransmission. This situation is fundamentally different from normal Internet mail. In the Internet mail case, either the system delivered the message, Burger Expires December 2002 [Page 8]
Critical Content of Internet Mail June 2002 or it didn't. There is no concept of a system partially delivering a message. In addition, there are many situations where the sender would not mind if the system did not deliver non-critical parts of a message. For example, the sender's user agent may add body parts to a message unbeknownst to the sender. If the receiving system rejected the message because it could not render a hidden body part, the sender would be understandably confused and upset. Thus, there is a need for a method of indicating to a Mail Transfer Agent (MTA) or User Agent (UA) that the sender considers parts of a message to be critical. From the sender's perspective, he would not consider the message delivered if the system did not deliver the critical parts. 8.2. Current Approaches One method of indicating critical content of a message is to define a profile. The profile defines rules for silently deleting mail body parts based on knowledge of the UA capabilities. Citing the example above, a voice profile can easily declare that MTAs or UAs can silently delete TNEF data and yet consider the message successfully delivered. This is, in fact, the approach taken by VPIMv2 [13]. Since one aspect of the issue is deciding when to notify the sender that the system cannot deliver part of a message, one could use a partial non-delivery notification mechanism to indicate a problem with delivering a given body part. However, this requires the user request a delivery notification. In addition, the sender may not be aware of parts added by the sending user agent. In this case, a failure notice would mystify the sender. A straightforward alternative implementation method for marking a body part critical is to use a Critical-Content MIME entity. This has the benefit that criticality is meta information for the body part. However, IMAP servers in particular would need to either put Critical-Content into the BODYSTRUCTURE method or create a new method to retrieve arbitrary MIME entities. Given the experience of trying to get Content-Location accepted by IMAP vendors, we chose not to go that route. What we need is a way of letting the sender indicate what body-parts he considers to be critical. The mechanism must not burden the sender with failure notifications for non-critical body parts. The mechanism must conform to the general notification status request mechanism for positive or negative notification. When requested, the mechanism must indicate to the sender when a receiving system cannot deliver a critical body part. Burger Expires December 2002 [Page 9]
Critical Content of Internet Mail June 2002 9. The Content Gateway In this section, we use the definition of [14] for the term "gateway." A content gateway is a gateway that connects a first network to a second network. The second network often has lesser capability than the first network. The canonical topology follows. "[MTA]", with square brackets, signifies an optional component. +---------+ +---------+ +-----+ | | +-------+ +-----------+ | Sending |=...=|[MTA]|===| Content |=...=| [MTA] |===| Receiving | | UA | +-----+ | Gateway | +-------+ | UA | +---------+ | | +-----------+ +---------+ First Network Second Network The content gateway can be the last hop before the receiving MTA. The content gateway can be between networks, and thus not the last hop before the receiving MTA. The content gateway can be the first MTA the sending UA contacts. Finally, the content gateway can be an integrated component of the receiving MTA. For the SIP case, consider each MTA as a SIP Proxy, the Sending UA as a SIP User Agent Client, and the Receiving UA as a SIP User Agent Server. 9.1. Integrated Content Gateway In this situation, the receiving user agent is integrated with the content gateway. The integrated content gateway knows the capabilities of the user agent. The topology is as follows. +---------------------+ +---------+ +-----+ | : | | Sending |=...=|[MTA]|===| Content : Receiving | | UA | +-----+ | Gateway : UA | +---------+ | : | +---------------------+ First Network Second Network The processing of ISUP and QSIG objects, as described in [4], is an example of an integrated gateway. Burger Expires December 2002 [Page 10]
Critical Content of Internet Mail June 2002 9.2. Disaggregated Delivery Network A degenerate case, although one that does occur, is where the content gateway sits behind the final MTA. This happens when one implements the content gateway as a post-processing step to a normal delivery. For example, one could configure a mail handling system to deliver the message to a queue or directory, where the content gateway process picks up the message. If there were any directives for DSN processing, the delivering MTA would execute them. For example, the message could have requested notification on successful delivery. The delivering MTA, having delivered the message to the queue, would consider the message delivered and thus notify the sender of such. However, the content gateway process could then discover that the receiving UA cannot render the message. In this case, the content gateway generates a NDN, as it is the only option available. Delivered | +---------+ +---------+ +-----+ v | | +-----------+ | Sending |=...=| MTA |--> File -->| Content |=...=| Receiving | | UA | +-----+ | Gateway | | UA | +---------+ | | +-----------+ +---------+ First Network Second Network 10. Backward Compatibility Considerations DSN requires ESMTP. If MTAs in the path from the sending UA to the receiving UA do not support ESMTP, then that MTA will reject the DSN request. In addition, the message will default to notification on delay or failure. While not ideal, the sender will know that DSN is not available, and that critical content that fails will get notification. 11. MIME Interactions 11.1. multipart/alternative As is true for all Content-Disposition parameters, handling is only in effect for the selected alternative. If the selected alternative has the critical content indicator, then the entire alternative takes on the criticality indicated. That is, if the alternative selected has HANDLING=OPTIONAL, then the content gateway MUST NOT generate any delivery notifications. NOTE: This statement explicitly shows that HANDLING overrides the DSN and MDN request mechanisms. Burger Expires December 2002 [Page 11]
Critical Content of Internet Mail June 2002 It is unlikely for a selected alternative to fail, as the content gateway presumably picks the alternative specifically because it can render it. If the selected alternative is a message/rfc822 that encloses a multipart MIME message or the selected alternative is itself a multipart MIME type, the individual top-level body parts follow the HANDLING mechanism described in this document. NOTE: This means that a forwarded message's criticality will not affect the forwarding agent's intentions. 11.2. multipart/related Criticality fits in rather well with the multipart/related construction. For example, consider a multipart/related message consisting of a Macintosh data fork and a Macintosh resource fork. For a Microsoft Word document, the data fork is likely to be critical. The receiving system can safely ignore the resource fork. 11.3. message/rfc822 Criticality only affects the outermost level of the message or, in the case of multipart/alternative, the outermost level of the selected alternative. Specifically, the receiving system ignores criticality indicators in embedded body parts. This avoids the situation of a forwarded message triggering or suppressing undesired reporting. This simply implements the procedures described in [5]. 12. Implementation Examples This section is not a normative part of the definition of Criticality. However, we hope it helps implementers to understand the mechanics of the Handling mechanism. We will examine two cases. They are how a content gateway processes a message and how a disaggregated content gateway processes a message. 12.1. Content Gateways Content gateways examine the contents of a message from a first network before the gateway forwards the message to a second network. For the purposes of this example, we assume the second network has less capability than the first network. In particular, we expect there will be certain message body types that the gateway cannot pass onto the second network. Consider a gateway between the Internet and a text-only short message service. A message comes through the gateway containing a text part and a tnef part. The sender marks the text part REQUIRED. Burger Expires December 2002 [Page 12]
Critical Content of Internet Mail June 2002 The gateway, knowing the capability of the short message service, silently deletes the non-critical, tnef part, passing the critical content to the short message service network. Any subsequent notifications, such as failure notices or delivery notices, follow the normal rules for notification. Note the gateway, by silently deleting non-critical content, may affect proprietary message correlation schemes. One can envision the sending UA inserting a body part for tracking purposes. By deleting non-critical content, the content gateway will break such a scheme. If a sending UA understands how to mark critical content, it should use Internet standard mechanisms for tracking messages, such as Message-ID [15]. What if no body parts have critical content indicators? In this case, the entire message is critical. Thus, when the gateway sees the tnef part, it will reject the entire message, generating a DSN with a status code 5.6.1, "Media not supported". Likewise, consider a three part message with a text annotation (part 1) to a voice message (part 2) with a vCard [16] (part 3). The sender marks the first two parts REQUIRED. Now, let us assume the receiving MTA (gateway) is a voice mail only system, without even the capability to store text. In this case, the gateway, acting as the receiving MTA, will reject the message, generating a DSN with the status code 5.6.1, "Media not supported". 12.2. Disaggregated Content Gateway For this example, we will examine the processing of a three-part message. The first part is a text annotation of the second part, an audio message. The third part is the sender's vCard. The sender marks the first and second parts REQUIRED. In addition, the sender marks the message for read receipt. For the purposes of example, the telephone user interface (TUI) does not perform text-to-speech conversion. A TUI is a mail user agent (UA) that uses DTMF touch-tone digits for input and audio for output (display). The TUI is unable to render the first part of the message, the text part. In addition, it is unable to render the third part of the message, the vCard part. Since the sender did not mark the third part of the message REQUIRED, the system ignores the failure of the TUI to render the third part of the message. However, since the sender did mark the first part REQUIRED, and the TUI is unable to render text, the message fails. What happens next is implementation dependent. If the TUI is part of a unified messaging system, a reasonable action is to hold the message for the user. The user can access the message at a later time from a terminal that can render all of the critical body parts. Burger Expires December 2002 [Page 13]
Critical Content of Internet Mail June 2002 It would be reasonable for the TUI to notify the user about the undeliverable body part. If the TUI is part of a voice messaging system, or if the user does not subscribe to a text-to-speech service, a reasonable action is for the TUI to return a MDN with the disposition "failed" and the failure modifier "5.6.1 (Media not supported)". 13. Security Considerations Receiving systems and users should not place any authentication value on the Handling parameter. Note that by design, and under the sending user's request, a content gateway will silently delete unimportant body parts. Critical content gives the sender the ability to determine the acceptable level integrity of the delivered message. That is, the message as the content gateway actually passes it on is, in fact, representative of the sender's intentions. 14. IANA Considerations RFC 3204 already registered the Handling parameter. It is collected here only for reference and as a placeholder for use both for further expansion in the future and as the normative reference for other documents that need to reference the Handling parameter. Per section 9 of [5] here is the IANA registration for Handling. To: IANA@IANA.ORG Subject: Registration of new Content-Disposition parameter Content-Disposition parameter name: HANDLING Allowable values for this parameter: REQUIRED OPTIONAL Description: Marks the body part as required for delivery (REQUIRED) or can be silently discarded (OPTIONAL). See RFC <this document> and RFC 3204. Per RFC 2183, the Content-Disposition parameter name is not case sensitive. Per RFC <this document>, the values of the parameter are also not case sensitive. Burger Expires December 2002 [Page 14]
Critical Content of Internet Mail June 2002 15. References 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. 2 Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 3 Handley, M., Schulzrinne, H., Schooler, E., and Rosenberg, J., "SIP: Session Initiation Protocol", RFC 2543, March 1999. 4 Zimmerer, E., et. al., "MIME media types for ISUP and QSIG Objects", RFC 3204, December 2001. 5 Troost, R., Dorner, S., Moore, K. (ed), "Communicating Presentation Information in Internet Messages: The Content- Disposition Header Field", RFC 2183, August 1997. 6 Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. 7 Moore, K., "SMTP Service Extension for Delivery Status Notifications", RFC 1981, January 1996. 8 Moore, K. and Vaudreuil, G., "An Extensible Message Format for Delivery Status Notifications", RFC 1894, January 1996. 9 Fajman, R., "An Extensible Message Format for Message Disposition Notifications", RFC 2298, March 1998. 10 Vaudreuil, G., "Enhanced Mail System Status Codes", RFC 1893, January 1996. 11 Freed, N. and Borenstein, N., "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. 12 Freed, N. and Borenstein, N., "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. 13 Vaudreuil, G. and Parsons, G., "Voice Profile for Internet Mail - version 2", RFC 2421, September 1998. 14 Kille, S. "MIXER (Mime Internet X.400 Enhanced Relay): Mapping between X.400 and RFC 822/MIME", RFC 2156, January 1998. 15 Crocker, D., "Standard for the Format of ARPA Internet Text Messages", RFC 822, August 1982. Burger Expires December 2002 [Page 15]
Critical Content of Internet Mail June 2002 16 Dawson, F. and Howes, T., "vCard MIME Directory Profile", RFC 2426, September 1998. 16. Acknowledgments Emily Candell of Comverse Network Systems was instrumental in helping work out the base issues in the รป00 draft in Adelaide. Ned Freed pointed out that this mechanism was about criticality, not notification. That insight made the concept and descriptions infinitely more straightforward. If it's still confusing, it's my fault! Keith Moore for helped tighten-up the explanations, and he approved of the use of Content-Disposition. Dropping the IMPORTANT critical content type took away one of the reasons for partial non-delivery notification. That makes Jutta Degener very happy! Harald Alvestrand and Chris Newman suggested some implementation examples. Greg White asked THE key question that let us realize that critical content processing was a gateway function, and not a MTA or UA function. Jon Peterson cleared up how handling actually does work in the SIP environment. An enormous thank you to Michelle S. Cotton at IANA for helping me craft the original IANA Considerations section in 2000, and for catching the functional overlap with RFC 3204 in January 2002. Any errors, omissions, or silliness are my fault. 17. Author's Address Eric Burger SnowShore Networks, Inc. 285 Billerica Rd. Chelmsford, MA 01824-4120 USA Phone: +1 978 367 8400 Fax: +1 603 457 5944 Email: e.burger@ieee.org Burger Expires December 2002 [Page 16]
Critical Content of Internet Mail June 2002 Full Copyright Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Copyright (C) 2000, 2001, 2002, The Internet Society. All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Burger Expires December 2002 [Page 17]
