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Versions: (draft-hoffman-rescap-mua) 00

RESCAP                                                        P. Hoffman
Internet-Draft                                  Internet Mail Consortium
Expires: December 23, 2002                                 June 24, 2002


                  RESCAP Profile for Mail User Agents
                      draft-ietf-rescap-mua-00.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   This Internet-Draft will expire on December 23, 2002.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document defines RESCAP Attributes for Mail User Agents (MUAs)
   and mail recipients.  Values for these attributes will contain
   information that a mail sender might want or need to know about a
   particular mail recipient before sending a message.











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1. Introduction

   This document defines Attributes for the RESCAP protocol for mail
   user agents (MUAs) and mail recipients.  It describes the attributes
   that a mail sender might want or need to know about a particular mail
   recipient before sending a message.

   The attributes are divided into four general categories:

   o  MIME handling

   o  S/MIME

   o  OpenPGP

   o  General

   Note: this list is very preliminary.  The process of defining the
   requirements for rescap has just begun.  Because the rescap protocol
   has not even had a first draft, it is likely that there will be many
   significant changes to this draft in the future as rescap gets worked
   on.

   In this document, "recipient" is used to indicate the user who can
   accept mail at the URL provided in the rescap request and "sender" is
   the person or process who requested the rescap information.  Note
   that some of the attributes in this document apply to the MUA a
   recipient is using, while others apply directly to the mail recipient
   (which might be a human or a mail-processing program).

   The attributes described in this document are those that a mail
   sender would want to know about a recipient or the recipient's MUA.
   Attributes about the mail recipient that have no relevance to a mail
   sender (such if the MUA uses IMAP to access its message store) are
   not included.
















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2. MIME Handling

   The attributes in this section describe general MIME handling.  They
   include some specific MIME profiles as well as more general MIME
   characteristics.

      Identifier:   urn:ietf:params:rescap:mua:PlainTextOnly
      Value type:   Boolean ("0" or "1")
      Description:  Can only read single-part text/plain messages.  Put
      another way, cannot parse a MIME message.

      Identifier:   urn:ietf:params:rescap:mua:MIMEIntlHeaders
      Value type:   Boolean ("0" or "1")
      Description:  Conforms to [3], which describes many extensions for
      MIME headers, such as for non-ASCII characters.

      Identifier:   urn:ietf:params:rescap:mua:MIMEParamExtensions
      Value type:   Boolean ("0" or "1")
      Description:  Conforms to [5], which describes many extensions for
      MIME parameter values and encoded words.

      Identifier:   urn:ietf:params:rescap:mua:DisplayableMedia
      Value type:   String
      Description:  A list of MIME types and subtypes that are natively
      displayed by the receiving MUA without falling back to a default
      media type.  The string is in the format of [12], as extended by
      [16].  This string should contain only MIME types and subtypes,
      not additional media features.

      Identifier:   urn:ietf:params:rescap:mua:MediaFeatures
      Value type:   String
      Description:  A list of media features of the MUA.  The string is
      in the format of [12].

      Identifier:   urn:ietf:params:rescap:mua:CharsetsDisplayed
      Value type:   Conneg string
      Description:  The list of charset labels that describe the
      charsets [6] that can be displayed.  Note that US-ASCII, and
      support for at least the US-ASCII subset of ISO-8859-*, is assumed
      regardless of the value of this attribute.  The string is in the
      format of [12], using the tags defined in [17].

      Identifier:   urn:ietf:params:rescap:mua:PreferredLanguages
      Value type:   List of strings
      Description:  The lists of languages understandable to the
      recipient, as described in [1].  The string is in the format of
      [12], using the tags defined in [CONNEG-CHARLANG].




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      Identifier:   urn:ietf:params:rescap:mua:LineLength
      Value type:   Integer
      Description:  The width, in characters, of a line in the display
      of the MUA.  For variable-width displays, this should be an
      estimate of the number of characters per line from a typical mail
      message.  For systems that have no line limitations, this value
      should be set to 0.

      Identifier:   urn:ietf:params:rescap:mua:HandlesMHTML
      Value type:   Boolean ("0" or "1)
      Description:  Handles MHTML content natively, as described in [4].

      Identifier:   urn:ietf:params:rescap:mua:HandlesContentMD5
      Value type:   Boolean ("0" or "1")
      Description:  Handles Content-MD5 headers, as described in [2].
      If the recipient does not handle Content-MD5 headers, as many
      don't, this the sender can save time by not constructing one.

      Identifier:   urn:ietf:params:rescap:mua:HandlesMailingListURLs
      Value type:   Boolean ("0" or "1")
      Description:  Handles mailing list URL headers, as described in
      [LIST-URLS].

      Identifier:   urn:ietf:params:rescap:mua:RepliesToMDNs
      Value type:   Boolean ("0" or "1")
      Description:  Is able to reply to message disposition notification
      requests, as described in [7].  Note that this does not mean that
      the client will necessarily send an MDN back to a particular
      request, just that it is able to reply to such requests.  This
      field helps a sending MUA decide whether or not to keep track of
      the MDNs sent to the recipient; if the recipient is known not to
      reply to MDNs, then the sender doesn't need to track them.  This
      can also reduce the size of messages sent over bandwidth-
      restricted lines.

      Identifier:   urn:ietf:params:rescap:mua:CalendarClient
      Value type:   Boolean ("0" or "1")
      Description:  Can act as an iCalendar iMIP agent [11].













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3. S/MIME

   The attributes in this section indicate the S/MIME capabilities of
   the recipient as described in [14], [13], and associated documents.

   Note that some S/MIME public keys are used for both encrypting and
   signing.  This means that there may be duplicated certificates in the
   SMIMESigningCertsBasic and SMIMEEncryptingCerts lists.

      Identifier:   urn:ietf:params:rescap:mua:SMIMEVerifiesSigned
      Value type:   List of strings
      Description:  Indicates that the recipient can verify the
      signatures on S/MIME signed messages.  The strings in the list
      indicate the type of signatures accepted.  The values currently
      are limited to "id-dsa" and "rsaEncryption".  The list is in
      decreasing order of preference.

      Identifier:   urn:ietf:params:rescap:mua:SMIMESigningCertsBasic
      Value type:   List of strings
      Description:  Provides the S/MIME certificates for public signing
      keys of the recipient.  The list is in decreasing order of
      preference.

      Identifier:   urn:ietf:params:rescap:mua:SMIMESigningCertsExtended
      Value type:   List of strings
      Description:  Provides the S/MIME certificates for public signing
      keys of the recipient.  The list is in decreasing order of
      preference.

      Identifier:   urn:ietf:params:rescap:mua:SMIMEEncryptingCerts
      Value type:   List of strings
      Description:  Provides the S/MIME certificates for public
      encrypting keys of the recipient.  The list is in decreasing order
      of preference.

      Identifier:   urn:ietf:params:rescap:mua:SMIMEHigherCerts
      Value type:   List of strings
      Description:  Provides the S/MIME certificates for certificate
      authorities that have signed the recipient's signing and
      encrypting certificates.  These higher-level certificates can be
      used by the sender to validate the recipient's certificates.  The
      list is in no particular order.

      Identifier:   urn:ietf:params:rescap:mua:SMIMESignedReceipts
      Value type:   Boolean ("0" or "1")
      Description:  Responds to requests for S/MIME signed receipts
      described in [15].




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      Identifier:   urn:ietf:params:rescap:mua:SMIMESecurityLabels
      Value type:   Boolean ("0" or "1")
      Description:  Acts on S/MIME security labels, or is behind a
      gateway that does security label handling, as described in [15].

      Identifier:   urn:ietf:params:rescap:mua:SMIMESecureMailingList
      Value type:   Boolean ("0" or "1")
      Description:  Is a mailing list that uses secure mailing list
      handling described in [15].

      Identifier:   urn:ietf:params:rescap:mua:SMIMEHandlesSigningCert
      Value type:   Boolean ("0" or "1")
      Description:  Handles the signed SigningCertificate attribute
      described in [15].





































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4. OpenPGP

   The attributes in this section indicate the OpenPGP capabilities of
   the recipient as described in [10] and associated documents.

      Identifier:   urn:ietf:params:rescap:mua:OpenPGPVerifiesSigned
      Value type:   List of strings
      Description:  Indicates that the recipient can verify the
      signatures on OpenPGP signed messages.  The strings in the list
      indicate the type of signatures accepted.  The values currently
      are limited to "DSA" and "RSA".  The list is in decreasing order
      of preference.

      Identifier:   urn:ietf:params:rescap:mua:OpenPGPSigningCertsBasic
      Value type:   List of strings
      Description:  Provides the OpenPGP certificates for public signing
      keys of the recipient.  The list is in decreasing order of
      preference.

      Identifier:   urn:ietf:params:rescap:mua:OpenPGPEncryptingCerts
      Value type:   List of strings
      Description:  Provides the OpenPGP certificates for public
      encrypting keys of the recipient.  The list is in decreasing order
      of preference.

      Identifier:   urn:ietf:params:rescap:mua:OpenPGPHigherCerts
      Value type:   List of strings
      Description:  Provides the OpenPGP certificates for users and
      certificate authorities that have signed the recipient's signing
      and encrypting certificates.  These higher-level certificates can
      be used by the sender to validate the recipient's certificates.
      The list is in no particular order.



















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5. General

   User agent and recipient attributes that don't fit into the other
   categories appear in this section.

      Identifier:   urn:ietf:params:rescap:mua:UBEPrefernces
      Value type:   List of strings
      Description:  Specifies the preferences of the recipient for
      receiving unsolicited bulk email (UBE).  Each entry in the list is
      a pair of strings.  The first entry in the pair is a tag
      indicating the law or policy being referred to, and the second
      entry is the value specified for that law or policy.  The
      identities of the laws and policies must be registered with IANA.

      Identifier:   urn:ietf:params:rescap:mua:MailingListInfo
      Value type:   String
      Description:  Gives information about a mailing list.  The format
      of the information is single string consisting of RFC 822 headers,
      as described in [8].  If the recipient is not a mailing list and
      this attribute is included in the rescap response, the string
      should be empty.

      Identifier:   urn:ietf:params:rescap:mua:GeneralInfo
      Value type:   vCard string
      Description:  Gives information about the person or system that is
      associated with the recipient.  The information is returned in the
      vCard format described in [9].  Note that any information in this
      attribute that can also be represented in other attributes in this
      profile should also be delivered in the other attributes.  No
      client should have to retrieve the value for this attribute in
      order to get information that is also available in other
      attributes.

      Identifier:   urn:ietf:params:rescap:mua:AssociatedEmailAddresses
      Value type:   List of lists
      Description:  Lists the email addresses used by this recipient.
      The list contains items that contain a pair of string items.  The
      pairs consist of an email address and a description.  The
      description should be the strings "home", "work", "all", "unused".
      The "unused" term indicates an email address that is no longer
      valid for the recipient.










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6. Security Considerations

   The rescap protocol will control the security of the passing the
   values for the attributes described here.  If digital signatures are
   not used, an attacker can alter the values that the client receives
   from the server, thereby causing false values or no values to be
   received.  For example, an attacker can change the legal notices
   sent, which can cause damage to the named recipient.  If encryption
   is not used, an attacker can watch the values of the attributes as
   they are transmitted over the Internet.









































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Normative References

   [1]   Alvestrand, H., "Tags for the Identification of Languages", RFC
         1766, March 1995.

   [2]   Myers, J. and M. Rose, "The Content-MD5 Header Field", RFC
         1864, October 1995.

   [3]   Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part
         Three: Message Header Extensions for Non-ASCII Text", RFC 2047,
         November 1996.

   [4]   Palme, J. and A. Hopmann, "MIME E-mail Encapsulation of
         Aggregate Documents, such as HTML (MHTML)", RFC 2110, March
         1997.

   [5]   Freed, N. and K. Moore, "MIME Parameter Value and Encoded Word
         Extensions: Character Sets, Languages, and Continuations", RFC
         2231, November 1997.

   [6]   Freed, N. and J. Postel, "IANA Charset Registration
         Procedures", BCP 19, RFC 2278, January 1998.

   [7]   Fajman, R., "An Extensible Message Format for Message
         Disposition Notifications", RFC 2298, March 1998.

   [8]   Baer, J. and G. Neufeld, "The Use of URLs as Meta-Syntax for
         Core Mail List Commands and their Transport through Message
         Header Fields", RFC 2369, July 1998.

   [9]   MISSING ORGANIZATION and MISSING ORGANIZATION, "vCard MIME
         Directory Profile", RFC 2426, September 1998.

   [10]  Callas, J., Donnerhacke, L., Finney, H. and R. Thayer, "OpenPGP
         Message Format", RFC 2440, November 1998.

   [11]  Dawson, F., Mansour, S. and S. Silverberg, "iCalendar Message-
         Based Interoperability Protocol (iMIP)", RFC 2447, November
         1998.

   [12]  Klyne, G., "A Syntax for Describing Media Feature Sets", RFC
         2533, March 1999.

   [13]  Ramsdell, B., "S/MIME Version 3 Certificate Handling", RFC
         2632, June 1999.

   [14]  Ramsdell, B., "S/MIME Version 3 Message Specification", RFC
         2633, June 1999.



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   [15]  Hoffman, P., "Enhanced Security Services for S/MIME", RFC 2634,
         June 1999.

   [16]  Klyne, G., "MIME Content Types in Media Feature Expressions",
         RFC 2913, September 2000.

   [17]  Hoffman, P., "Registration of Charset and Languages Media
         Features Tags", RFC 2987, November 2000.


Author's Address

   Paul Hoffman
   Internet Mail Consortium
   127 Segre Place
   Santa Cruz, CA  95060
   USA

   EMail: paul.hoffman@imc.org and paul.hoffman@vpnc.org
































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Appendix A. IANA Registrations

A.1 Attribute Identifier Registrations

   [[It is likely that all the attribute identifiers in this document
   will need to be registered.]]

A.2 Additional Registrations

   [[Registration of UCE law and policy identifiers]]









































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Appendix B. Acknowledgments

   The following people have contributed changes and additions to this
   document:

      Chris Newman

      Graham Klyne

      Larry Masinter

      Tony Hansen







































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Appendix C. Changes between versions of the draft

   Updated to reflect changes in the base RESCAP protocol.
   Specifically, Attribute Names are now URIs















































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Full Copyright Statement

   Copyright (C) The Internet Society (2002).  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
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   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
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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