Internet DRAFT - draft-ietf-vpim-hint


Network Working Group                                           E. Burger 
Internet Draft                                         SnowShore Networks 
Document: draft-ietf-vpim-hint-08.txt                          E. Candell 
Category: Standards Track                                        Comverse 
Expires December 2002                                            C. Eliot 
                                                    Microsoft Corporation 
                                                                 G. Klyne 
                                                   Clearswift Corporation 
                                                             June 5, 2002 
                   Message Context for Internet Mail 
Status of this Memo 
   This document is an Internet-Draft and is in full conformance with 
   all provisions of Section 10 of RFC2026 [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-
   Internet-Drafts are draft documents valid for a maximum of six 
   months and may be updated, replaced, or obsoleted by other documents 
   at any time. It is inappropriate to use Internet-Drafts as reference 
   material or to cite them other than as "work in progress." 
   The list of current Internet-Drafts can be accessed at . 
   The list of Internet-Draft Shadow Directories can be accessed at . 
   This document is a work product of the IETF Voice Profile for 
   Internet Mail (VPIM) Work Group. 
1. Abstract 
   This memo describes a new RFC2822 message header, "Message-Context".  
   This header provides information about the context and presentation 
   characteristics of a message. 
   A receiving user agent (UA) may use this information as a hint to 
   optimally present the message. 

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Table of Contents 
1. Abstract...........................................................1 
2. Introduction.......................................................3 
3. Conventions used in this document..................................3 
4. Motivation.........................................................4 
5. Functional Requirements............................................5 
6. Determining the Message Context....................................6 
7. Message-Context Reference Field....................................7 
7.1. Message-Context Syntax...........................................7 
7.2. message-context-class Syntax.....................................7 
7.2.1. voice-message..................................................8 
7.2.2. fax-message....................................................8 
7.2.3. pager-message..................................................8 
7.2.4. multimedia-message.............................................8 
7.2.5. text-message...................................................8 
7.2.6. none...........................................................8 
8. Security Considerations............................................9 
9. IANA Considerations................................................9 
9.1. Message Content Type Registrations..............................10 
9.2. Registration Template...........................................10 
9.3. Message-Context Registration....................................11 
10. APPENDIX: Some messaging scenarios...............................11 
10.1. Internet e-mail................................................11 
10.2. Pager service..................................................12 
10.3. Facsimile......................................................13 
10.4. Voice mail.....................................................13 
10.5. Multimedia message.............................................13 
11. References.......................................................14 
12. Acknowledgments..................................................15 
13. Author's Addresses...............................................15 
14. Full Copyright Statement.........................................17 

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2. Introduction 
   This document describes a mechanism to allow senders of an Internet 
   mail message to convey the message's contextual information.  Taking 
   account of this information, the receiving user agent (UA) can make 
   decisions that improve message presentation for the user in the 
   context the sender and receiver expects. 
   In this document, the "message context" conveys information about 
   the way the user expects to interact with the message.  For example, 
   a message may be e-mail, voice mail, fax mail, etc.  A smart UA may 
   have specialized behavior based on the context of the message. 
   This document specifies a RFC2822 header called "Message-Context".  
   The mechanism is in some ways similar to the use of the Content-
   Disposition MIME entity described in [2].  Content-Disposition gives 
   clues to the receiving User Agent (UA) for how to display a given 
   body part.  Message-Context can give clues to the receiving UA for 
   the presentation of the message.  This allows the receiving UA to 
   present the message in a meaningful and helpful way to the 
   Typical uses for this mechanism include: 
   o    Selecting a special viewer for a given message. 
   o    Selecting an icon indicating the kind of message in a displayed 
        list of messages. 
   o    Arranging messages in an inbox display. 
   o    Filtering messages the UA presents when the user has limited 
3. 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 
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   this document are to be interpreted as described in RFC-2119 [3]. 
   FORMATTING NOTE: Notes, such at 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. 
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4. Motivation 
   Multimedia messaging systems receive messages that a UA may present 
   in variety of ways.  For example, traditional e-mail uses simple 
   text messages that the recipient displays and edits.  One UA may 
   automatically print Fax images.  Another UA may play voice messages 
   through a telephone handset.  Likewise, a receiving desktop computer 
   may process or present documents transferred over e-mail using a 
   local application.  Emerging and future developments may deliver 
   other forms of information that have their own characteristics for 
   user presentation, such as video messages and pager messages. 
   An often-requested characteristic for multimedia messaging systems 
   is to collect received messages in a "universal inbox", and to offer 
   them to the user as a combined list. 
   In the context of "unified messaging", different message contexts 
   may have different implied semantics.  For example, some users may 
   perceive voicemail to have an implicit assumption of urgency.  Thus 
   they may wish to gather them together and process them before other 
   messages.  This results in the end-user receiving agent needing to 
   be able to identify voicemail and distinguish it from other 
   The uses of this kind of presentation characteristic for each 
   message is multi-fold: 
   o    Display an indication to the user (e.g., by a suitably 
        evocative icon along with other summary fields), 
   o    Auto-forward a given message type into another messaging 
        environment (e.g., a page to a mobile short message service), 
   o    Prioritize and group messages in an inbox display list, 
   o    Suggest appropriate default handling for presentation, 
   o    Suggest appropriate default handling for reply, forward, etc., 
   A problem faced by multimedia messaging systems is that it is not 
   always easy to decide the context of a received message.  For 
   example, consider the following scenarios. 
   o    A message that contains audio and image data:  Is this a fax 
        message that happens to have some voice commentary?  Is it a 
        voice message that is accompanied by some supplementary 
        diagrams?  Is it a fully multimedia message, in which all parts 
        are expected to carry equal significance? 

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   o    A message containing text and audio data:  Is this e-mail with 
        an MP3 music attachment?  Is it a voice message that happens to 
        have been generated with an initial text header for the benefit 
        of non-voice-enabled e-mail receivers? 
   The message context does relate to the message media content.  
   However, it is not the same thing.  As shown above, the media type 
   used in a message is not sufficient to indicate the message context.  
   One cannot determine a priori which media types to use in 
   alternative (gateway) message.  Also, what if the user cares about 
   distinguishing traditional e-mail text from SMS messages?  They are 
   both the same media type, text, but they have different user 
5. Functional Requirements 
   The goals stated above lead to the following functional 
   For receivers: 
   o    Identify a message as belonging to a message class. 
   o    Incorrect or invalid message classification must not result in 
        failure to transfer or inability to present a message. 
   For senders: 
   o    Specify message classes by the originating user's choice of 
        authoring tool or simple user interaction. 
   For both: 
   o    Specify a well-defined set of message classes to make 
        interoperability between mail user agents (UAs) possible. 
   o    Message classification information has to be interpretable in 
        reasonable fashion by many different user agent systems. 
   o    The mechanism should be extensible to allow for the 
        introduction of new kinds of messages. 
   NOTE: We specifically do not specify user agent behavior when the 
   user agent forwards a message.  Clearly, the user agent, being 
   message-context-aware, should provide a meaningful message-context.  
   It is obvious what to do for the easy cases.  Messages that the user 
   simply forwards will most likely keep the context unchanged.  
   However, it is beyond the scope of this document to specify the user 
   agent behavior for any other scenario. 

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6. Determining the Message Context 
   One method of indicating the interpretation context of a message is 
   to examine the media types in the message.  However, this requires 
   the UA to scan the entire message before it can make this 
   determination.  This approach is particularly burdensome for the 
   multi-media mail situation, as voice and especially video mail 
   objects are quite large. 
   We considered indicating the message context by registering a 
   multipart/* MIME subtype (Content-Type).  For example, the VPIM Work 
   Group has registered multipart/voice-message to indicate that a 
   message is primarily voice mail [4].  However, multipart/voice-
   message is identical in syntax to multipart/mixed.  The only 
   difference is that VPIM mail transfer agents and user agents 
   recognize that they can perform special handling of the message 
   based on it being a voice mail message.  Moreover, Content-Type 
   refers to a given MIME body part, not to the message as a whole. 
   We wish to avoid scanning the entire message.  In addition, we wish 
   to avoid having to create multiple aliases for multipart/mixed every 
   time someone identifies a new primary content type.  Multiple 
   aliases for multipart/mixed are not desirable as they remove the 
   possibility for specifying a message as multipart/alternate, 
   multipart/parallel, or multipart/encrypted, for example. 
   Since the message context is an attribute of the entire message, it 
   is logical to define a new top-level (RFC2822 [5]) message 
   attribute.  To this end, this document introduces the message 
   attribute "Message-Context". 
   Message-Context only serves to identify the message context.  It 
   does not provide any indication of content that the UA must be 
   capable of delivering.  It does not imply any message disposition or 
   delivery notification.  There is a related effort to define Critical 
   Content of Internet Mail [6] that one might use to perform these 
   Message-Context is only an indicator.  We do not intend for it to 
   convey information that is critical for presentation of the message.  
   One can conceive of goofy situations, such as a message marked 
   "voice-message" but without an audio body part.  In this case, the 
   fact that the contents of a message don't match its context does not 
   mean the receiving system should generate an error report or fail to 
   deliver or process the message.  

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7. Message-Context Reference Field 
   The Message-Context reference field is a top-level header inserted 
   by the sending UA to indicate the context of the message. 
   A receiving user agent MUST NOT depend on the indicated message-
   context value in a way that prevents proper presentation of the 
   message.  If the value is incorrect or does not match the message 
   content, the receiving user agent MUST still be capable of 
   displaying the message content at least as meaningfully as it would 
   if no Message-Context value were present. 
   One can envision situations where a well-formed message ends up not 
   including a media type one would expect from the message-context. 
   For example, consider a voice messaging system that records a voice 
   message and also performs speech-to-text processing on the message.  
   The message then passes through a content gateway, such as a 
   firewall, that removes non-critical body parts over a certain 
   length.  The receiving user agent will receive a message in the 
   voice-message context that has only a text part and no audio.  Even 
   though the message does not have audio, it is still in the voice 
   message context. 
   Said differently, the receiving UA can use the message-context to 
   determine whether, when, and possibly where to display a message.  
   However, the message-context should not affect the actual rendering 
   or presentation.  For example, if the message is in the voice-
   message context, then don't try to send it to a fax terminal.  
   Conversely, consider the case of a message in the voice-message 
   context that gets delivered to a multimedia voice terminal with a 
   printer.  However, this message only has fax content.  In this 
   situation, the "voice-message" context should not stop the terminal 
   from being properly rendering the message. 
7.1. Message-Context Syntax 
   The syntax of the Message-Context field, described using the ABNF 
   [7] is as follows.  Note that the Message-Context header field name 
   and message-context-class values are not case sensitive. 
        "Message-Context" ":" message-context-class CRLF 
7.2. message-context-class Syntax 
   The message-context-class indicates the context of the message.  
   This is an IANA registered value.  Current values for message-
   context-class are as follows. 

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        message-context-class =  (   "voice-message" 
                                   / "fax-message" 
                                   / "pager-message" 
                                   / "multimedia-message" 
                                   / "text-message" 
                                   / "none" 
   Note: The values for Message-Context MUST be IANA registered values 
   following the directions in the IANA Considerations section below. 
7.2.1. voice-message 
   The voice-message class states the message is a voice mail message. 
7.2.2. fax-message 
   The fax-message class states the message is a facsimile mail 
7.2.3. pager-message 
   The pager-message class states the message is a page, such as a text 
   or numeric pager message or a traditional short text message service 
   (SMS) message. 
7.2.4. multimedia-message 
   The multimedia-message class states the message is an aggregate 
   multimedia message, such as a message specified by [8].  This helps 
   identify a message in a multimedia context.  For example, a MIME 
   multipart/related [9] data part and resource part looks the same as 
   a multimedia MHTML multipart/related.  However, the semantics are 
   quite different. 
7.2.5. text-message 
   The text-message class states the message is a traditional internet 
   mail message.  Such a message consists of text, possibly richly 
   formatted, with or without attachments. 
7.2.6. none 
   The none class states there is no context information for this 
   If a message has no Message-Context reference field, a receiving 
   user agent MUST treat it the same as it would if the message has a 
   "none" value. 
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8. Security Considerations 
   The intention for this header is to be an indicator only of message 
   context.  One can imagine someone creating an "Application" Message-
   Context.  A poorly designed user agent could blindly execute a 
   mailed program based on the Message-Context.  Don't do that! 
   One can envision a denial of service attack by bombing a receiver 
   with a message that has a Message-Context that doesn't fit the 
   profile of the actual body parts.  This is why the receiver 
   considers the Message-Context to be a hint only. 
9. IANA Considerations 
   Section 9.3 is a registration for a new top-level RFC2822 [5] 
   message header, "Message-Context".   
   This document creates an extensible set of context types.  To 
   promote interoperability and coherent interpretations of different 
   types, we need a central repository for well-known context types. 
   IANA will create a repository for context types called "Internet 
   Message Context Types".  Following the policies outlined in [10], 
   this repository is "Specification Required" by RFC.  Section 9.1 
   describes the initial values for this registry. 
   To create a new message context type, you MUST publish an RFC to 
   document the type.  In the RFC, include a copy of the registration 
   template found in Section 9.2 of this document.  Put the template in 
   your IANA Considerations section, filling-in the appropriate fields.  
   You MUST describe any interoperability and security issues in your 

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9.1. Message Content Type Registrations 
   Internet Message Content Types 
   Value              Description                           Reference 
   -----              -----------                           --------- 
   voice-message      Indicates a message whose primary     This RFC 
                      content is a voice mail message.  The 
                      primary content is audio data.  The 
                      context is usually a message recorded 
                      from a voice telephone call. 
   fax-message        Indicates a message whose primary     This RFC 
                      content is a fax mail message.  The 
                      primary content is image data.  The 
                      context is usually a message recorded 
                      from a facsimile telephone call. 
   pager-message      Indicates a message whose primary     This RFC 
                      content is a page.  The primary 
                      content is text data.  The context is 
                      an urgent message usually of a 
                      limited length. 
   multimedia-message Indicates a message whose primary     This RFC 
                      content is a multimedia message.  The 
                      primary content is multimedia, most 
                      likely MHTML.  The context is often 
                      spam or newsletters. 
   text-message       Indicates a classic, text-based,      This RFC 
                      Internet message. 
   None               Indicates an unknown message context. This RFC 
9.2. Registration Template 
   In the following template, a pipe symbol, "|", precedes instructions 
   or other helpful material.  Be sure to replace "<classname>" with 
   the class name you are defining. 
   Message-Context class name: 
   Summary of the message class: 
       | Include a short (no longer than 4 lines) description or summary 
       | Examples: 
       |   "Palmtop devices have a 320x160 pixel display, so we can..." 
       |   "Color fax is so different than black & white that..." 
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   Person & email address to contact for further information: 
       | Name & e-mail 
9.3. Message-Context Registration 
   Subject: Registration of New RFC 2822 Header 
   RFC 2822 Header Name: 
   Allowable values for this parameter: 
   Please create a new registry for Primary Context Class 
   registrations.  See section 9.1 of this document for the initial 
   RFC 2822 Section 3.6 Repeat Value: 
   Field             Min Number   Max Number   Notes 
   Message-Context       0            1         
   Person & email address to contact for further information: 
   Eric Burger                                           
10. APPENDIX: Some messaging scenarios 
   This section is not a normative part of this document.  We include 
   it here as a historical perspective on the issue of multimedia 
   message types. 
   These scenarios are neither comprehensive nor fixed.  For example, 
   e-mails being typically text-based do not mean that they cannot 
   convey a voice-message.  This very mutability serves to underline 
   the desirability of providing some explicit message context hint. 
10.1. Internet e-mail 
   Internet e-mail carries textual information.  Sometimes it conveys 
   computer application data of arbitrary size. 
   Typically, one uses e-mail for non-urgent messages, which the 
   recipient will retrieve and process at a time convenient to her. 
   The normal device for receiving and processing e-mail messages is 
   some kind of personal computer.  Modern personal computers usually 
   come with a reasonably large display and an alphanumeric keyboard.  
   Audio, video, and printing capabilities are not necessarily 
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   One can use E-mail for communication between two parties (one-to-
   one), a small number of known parties (one-to-few) or, via an e-mail 
   distribution list, between larger numbers of unknown parties (one-
   One of the endearing characteristics of e-mail is the way that it 
   allows the recipient to forward all or part of the message a to 
   another party, with or without additional comments.  It is quite 
   common for an e-mail to contain snippets of content from several 
   previous messages. Similar features apply when replying to e-mail. 
10.2. Pager service 
   One uses a pager message to convey notifications and alerts.  For 
   the most part, these notifications are textual information of 
   limited size.  The typical limit is 160 characters.  People use 
   pages for relatively urgent messages, which the sender wishes the 
   receiver to see and possibly respond to within a short time period.  
   Pager messages are often used as a way of alerting users to 
   something needing their attention.  For example, a system can use a 
   page to notify a subscriber there is a voicemail message requiring 
   her attention.   
   Example devices for sending and receiving a pager message are a 
   mobile telephone with a small character display or a text pager.  
   Personal computers and personal digital assistants (PDAs) can also 
   participate in pager messaging. 
   Currently, the most common use of pager messages are between just 
   two parties (one-to-one). 
   One delivery method for pager messages is the short text messaging 
   service (SMS).  SMS is a facility that has evolved for use with 
   mobile telephones, and has an associated per-message transmission 
   charge.  Note that the focus here is on the notification aspect of 
   SMS.  From the beginning, SMS was envisioned to be more than a 
   simple pager service.  Operators can use SMS to provision the phone, 
   for example.  From the subscriber point of view, SMS has evolved 
   considerably from its origins as a pure pager replacement service.  
   For example, with mobile originate service, people can have two-way 
   text chat sessions using SMS and a mobile phone.  In addition, there 
   are SMS-enabled handsets that can display pictures.  However, for 
   the purposes of this document, there is still a need to capture the 
   essence of a "highly urgent, short-text, notification or alert" 
   Users often send pager messages in isolation, rather than as part of 
   a longer exchange.  One use for them is as a prompt or invitation to 
   communicate by some more convenient and content-rich method, such as 
   a telephone call. 

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10.3. Facsimile 
   People use facsimile to convey image information of moderate size, 
   typically a small number of pages.  Sometimes people use facsimile 
   for larger documents. 
   Facsimile is a facility that usually uses circuit-switched telephone 
   circuits, with connection-time charges.  Message transfer takes 
   place in real-time.  Thus, people often use facsimile for urgent 
   The normal device for sending and receiving a facsimile is a self-
   contained scanning and printing device connected to a telephone line 
   or a desktop computer. 
   Most facsimiles are between just two parties (one-to-one).  However, 
   a significant portion of facsimile service is broadcast between 
   multiple parties (one-to-many). 
   Most facsimile exchanges are in isolation, rather than as part of a 
   longer exchange.  Facsimile data is typically not suitable for 
   further processing by computer. 
10.4. Voice mail 
   People use voice mail to convey audio information, almost 
   exclusively human speech. 
   Voice mail is a facility that usually uses circuit-switched 
   telephone circuits, with modest connection-time charges, often used 
   for moderately urgent messages.  A common use for them is as a 
   prompt or invitation to communicate by some more convenient method, 
   such as a telephone call. In most, but not all cases, the sender of 
   a voice message does not want to send a message at all.  Rather, 
   they wished to engage in a real-time conversation. 
   The normal device for sending and receiving a voice mail is a 
   telephone handset. 
   Voice messages are usually sent between just two parties (one-to-
   Voice mail data is not generally suitable for further processing by 
10.5. Multimedia message 
   We define a multimedia message as a message containing more than one 
   basic media type (text, image, audio, video, model, application). 
   The following are some characteristics of a multimedia message. 
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   In some cases, a multimedia message is just e-mail with an 
   attachment that a multimedia display application presents.  For 
   example, I can send you an MP3 of something I recorded in my garage 
   In other cases, a multimedia message represents a convergence 
   between two or more of the scenarios described above.  For example, 
   a voice message with an accompanying diagram or a talking head video 
   message is a multimedia message. 
   The characteristics will vary somewhat with the intent of the 
   sender.  This in turn may affect the user agent or application used 
   to render the message. 
11. References 
   1  Bradner, S., "The Internet Standards Process -- Revision 3", BCP 
      9, RFC 2026, October 1996. 
   2  Troost, R., Dorner, S., and Moore, K., "Communicating 
      Presentation Information in Internet Messages: The Content-
      Disposition Header Field", RFC 2183, New Century Systems, 
      QUALCOMM Incorporated, and University of Tennessee, August 1997. 
   3  Bradner, S., "Key words for use in RFCs to Indicate Requirement 
      Levels", BCP 14, RFC 2119, March 1997. 
   4  Vaudreuil, G. and Parsons, G., "VPIM Voice Message MIME Sub-type 
      Registration", RFC 2423, Lucent Technologies and Northern 
      Telecom, September 1998. 
   5  Resnick, P., "Internet Message Format", RFC 2822, Qualcomm, April 
   6  Burger, E., "Critical Content of Internet Mail", draft-ietf-vpim-
      cc-04.txt, Work in Progress. 
   7  Crocker, D. and Overell, P. (Editors), "Augmented BNF for Syntax 
      Specifications: ABNF", RFC 2234, Internet Mail Consortium and 
      Demon Internet Ltd., November 1997. 
   8  Palme, J., Hopmann, A., Shelness, N., "MIME Encapsulation of 
      Aggregate Documents, such as HTML (MHTML)", RFC 2557, Stockholm 
      University/KTH, Microsoft, and Lotus Development Corporation, 
      March 1999. 
   9 Levinson, E., "The MIME Multipart/Related Content-type", RFC 2387, 
      August 1998. 
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   10 Alvestrand, H. and T. Narten, "Guidelines for Writing an IANA 
      Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. 
12. Acknowledgments 
   Many of the ideas here arose originally from a discussion with Jutta 
   We'd also like to thank Keith Moore for helping us tighten-up our 
   In the last round, we got some rather good advise from Caleb Clausen 
   and Dave Aronson.  
   Antti Vaha-Sipila pointed out advances in SMS, while Stuart McRae 
   helped distil the essence of the pager service vis a vis SMS. 
   We offer an extra special thanks to Greg Vaudreuil for pulling RFC 
   2557 out of his hat. 
13. Author's Addresses 
   Eric Burger 
   SnowShore Networks, Inc. 
   285 Billerica Rd. 
   Chelmsford, MA  01824-4120 
   Phone: +1 978 367 8403 
   Fax:   +1 603 457 5944 
   Emily Candell 
   Comverse Network Systems 
   200 Quannapowitt Pkwy. 
   Wakefield, MA  01880 
   Phone: +1 781 213 2324 

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   Graham Klyne 
   Clearswift Corporation 
   MIMEsweeper Group 
   1310 Waterside 
   Arlington Business Park 
   Theale, Reading  RG7 4SA 
   United Kingdom 
   Telephone: +44 118 930 8903 
   E-mail:    GK@ACM.ORG 
   Charles Eliot 
   Microsoft Corporation 
   One Microsoft Way  
   Redmond WA 98052  
   Telephone: +1 425 936 9760 

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14. Full Copyright Statement 
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   pertain to the implementation or use of the technology described in 
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   claims of rights made available for publication and any assurances 
   of licenses to be made available, or the result of an attempt made 
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   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 
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