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rfc:rfc1495

Network Working Group H. Alvestrand Request for Comments: 1495 SINTEF DELAB Updates: 1327 S. Kille

                                                      ISODE Consortium
                                                              R. Miles
                                                     Soft*Switch, Inc.
                                                               M. Rose
                                          Dover Beach Consulting, Inc.
                                                           S. Thompson
                                                     Soft*Switch, Inc.
                                                           August 1993
          Mapping between X.400 and RFC-822 Message Bodies

Status of this Memo

 This RFC specifies an IAB standards track protocol for the Internet
 community, and requests discussion and suggestions for improvements.
 Please refer to the current edition of the "IAB Official Protocol
 Standards" for the standardization state and status of this protocol.
 Distribution of this memo is unlimited.

Table of Contents

 1.  Introduction .............................................    1
 2.  Approach .................................................    2
 3.  Mapping between X.400 and RFC-822 Message Bodies .........    3
 3.1  Mapping from X.400 to RFC-822 ...........................    4
 3.2  Mapping from RFC-822 to X.400 ...........................    5
 3.2.1 Asymmetric Mappings ....................................    6
 3.2.1.1 Message/External-Body ................................    6
 3.2.1.2 Message/Partial ......................................    6
 3.2.1.3 Nested Multipart Content-types .......................    6
 3.2.2 Multipart IPMS Heading Extension .......................    7
 4.  Mapping between X.400 and RFC-822 Message Headers ........    7
 5.  OID Assignments ..........................................    9
 6.  Security Considerations ..................................    9
 7.  Authors' Addresses .......................................   10
 8.  References ...............................................   11

1. Introduction

 The Internet community is a large collection of networks under
 autonomous administration, but sharing a core set of protocols.
 These are known as the Internet suite of protocols (or simply
 "TCP/IP").
 Use of electronic-mail in the Internet is defined primarily by one

Alvestrand, Kille, Miles, Rose & Thompson [Page 1] RFC 1495 MHS/RFC-822 Message Body Mapping August 1993

 document, STD-11, RFC-822 [1], which defines the standard format for
 the exchange of messages.  RFC-822 has proven immensely popular; in
 fact, the 822-connected Internet, is larger than the scope of the
 IP-connected Internet.
 The framework provided by RFC-822 allows for memo-based textual
 messages.  Each message consists of two parts:  the headers and the
 body.  The headers are analogous to the structured fields found in an
 inter-office memo, whilst the body is free-form.  Both parts are
 encoded using ASCII.
 Recently, the Internet Engineering Task Force (IETF) has developed an
 document called,
    Multipurpose Internet Mail Extensions
 or MIME RFC-1341.  The title is actually misleading.  MIME defines
 structure for Internet message bodies.  It is not an extension to
 RFC-822.
 Independently of this, the International standards community
 developed a different framework in 1984 (some say that's the
 problem).  This framework is known as the OSI Message Handling System
 (MHS) or sometimes X.400.
 Since the introduction of X.400(84), there has been work ongoing for
 defining mappings between MHS and RFC-822.  The most recent work in
 this area is RFC-1327 [3], which focuses primarily on translation of
 envelope and headers.  This document is complimentary to RFC-1327 as
 it focuses on translation of the message body.  The mappings defined
 are largely symmetrical with respect to MIME and MHS structuring
 semantics, although the MIME semantics are somewhat richer.  In order
 to provide for reversible transformations, MHS heading extensions are
 used to carry the additional MIME semantics.
 Please send comments to the MIME-MHS mailing list:
 <mime-mhs@surfnet.nl>.

2. Approach

 The mappings have been specifically designed to provide optimal
 behavior for three different scenarios:
 (1) Allow a MIME user and an MHS user to exchange an arbitrary binary
     content;
 (2) Allow MIME content-types to "tunnel" through an MHS relay that
     is, two MIME users can exchange content-types without loss

Alvestrand, Kille, Miles, Rose & Thompson [Page 2] RFC 1495 MHS/RFC-822 Message Body Mapping August 1993

     through an MHS relay); and,
 (3) Allow MHS body parts to "tunnel" through a MIME relay that is,
     two MHS users can exchange body parts without loss through a MIME
     relay).
 Other, related, scenarios can also be easily accommodated.
 To facilitate the mapping process, the Internet Assigned Numbers
 Authority (IANA) maintains a table termed the "IANA MHS/MIME
 Equivalence Table".  Once an enterprise has registered an OID to
 describe an MHS body part, it should complete a corresponding
 registry with the IANA for a MIME content-type/subtype.  In practice,
 the corresponding content-type will be "application", with an
 appropriate choice of sub-type and possible parameters.  If a new
 MIME content-type/subtype is registered with the IANA without a
 corresponding entry in the Equivalence Table, the IANA will assign it
 an OID, from the arc defined in this memo. See [4], section 5 for
 details.
 The companion document, "Equivalences between 1988 X.400 and RFC-822
 Message Bodies"[4], defines the initial configuration of this table.
 The mappings described in both this document and the companion
 document use the notational conventions of RFC-1327.

3. Mapping between X.400 and RFC-822 Message Bodies

 MHS messages are comprised of an IPMS.heading and an IPMS.body.  The
 IPMS.Body is a sequence of IPMS.BodyParts.  An IPMS.BodyPart may be a
 nested message (IPMS.MessageBodyPart).
 A MIME message consists of headers and a content.  For the purpose of
 discussion, the content may be structured (multipart or message), or
 atomic (otherwise).  An element of a structured content may be a
 message or a content.  Both message and structured content have
 subtypes which do not have direct analogies in MHS.
 The mapping between X.400 and RFC-822 message bodies which this
 document defines is symmetrical for the following cases:
        (1) any atomic body part
        (2) multipart: digest and mixed subtypes
        (3) message/rfc822
 RFC-1327 specifies the mappings for headers.  Section 4 describes how
 those mappings are modified by this document.  When mapping between

Alvestrand, Kille, Miles, Rose & Thompson [Page 3] RFC 1495 MHS/RFC-822 Message Body Mapping August 1993

 an MHS body and a MIME content, the following algorithm is used:

3.1. Mapping from X.400 to RFC-822

 This section replaces the text in RFC-1327 starting at the bottom of
 page 84,
     The IPMS.Body is mapped into the RFC-822 message body.  Each
     IPMS.BodyPart is converted to ASCII as follows:
 and continuing up to and including page 86 of Section 5.3.4 of RFC-
 1327.
           If the IPMS.Body
                Body ::=
                    SEQUENCE OF
                        BodyPart
 consists of a single body part, then the RFC-822 message body is
 constructed as the MIME content corresponding to that body part.
 If the body part is an IPMS.MessageBodyPart (forwarded IPM), the
 mapping is applied recursively.  Otherwise, to map a specific MHS
 body part to a MIME content-type, the IANA MHS/MIME Equivalence table
 is consulted.  If the MHS body part is not identified in this table,
 then the body-part is mapped onto an "application/x400-bp" content,
 as specified in [4].
 If the IPMS.Body consists of more than one body part, then the RFC-
 822 message body is constructed as a
        multipart/mixed
 content-type, unless all of the body parts are messages, in which
 case it is mapped to a
        multipart/digest
 content-type.  Each component of the multipart content-type
 corresponds to a IPMS.BodyPart, preserving the ordering of the body
 parts in the IPMS.Body.
 There is one case which gets special treatement.  If the IPMS.Body
 consists solely of a single IA5Text body part, then the RFC822
 message body is NOT marked as a MIME content.  This prevents RFC822
 mailers from invoking MIME function unnecessarily.

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3.2. Mapping from RFC-822 to X.400

 First, replace the first paragraph of Section 5.1.3 on page 72 of
 RFC-1327 to read as:
     The IPM (IPMS Service Request) is generated according to the
     rules of this section.  The IPMS.body usually consists of one
     IPMS.BodyPart of type
                         IPMS.IA5TextBodyPart
                    with
                         IPMS.IA5TextBodyPart.parameters.repertoire
     set to the default (ia5), which contains the body of the RFC-822
     message.  However, if the 822.MIME-Version header field is
     present, a special algorithm is used to generate the IPMS.body.
     Second, replace the "Comments:" paragraph on page 74 to reads as:
     Comments:
        If an 822.MIME-Version header field is not present,
        generate an IPMS.Bodypart of type
            IPMS.IA5TextBodyPart
        with
            IPMS.IA5TextBodyPart.parameters.repertoire
        set to the default (ia5), containing the value of
        the fields, preceded by the string "Comments: ".
        This body part shall preceed the other one.
 Third, add the remainder of this section to the end of Section 5.1.3
 of RFC-1327.
 If the 822.MIME-Version header field is present, the following
 mapping rules are used to generate the IPMS.body.
 If the MIME content-type is one of:
 (1)  any atomic body part
 (2)  multipart: digest and mixed subtypes

Alvestrand, Kille, Miles, Rose & Thompson [Page 5] RFC 1495 MHS/RFC-822 Message Body Mapping August 1993

 (3)  message/rfc822
 then the symmetric mapping applies as described in Section 6.1.  Note
 that the multipart content-types should be marked with the
 IPMS.HeadingExtension described below.
 Otherwise, three cases remain, which are discussed in turn.

3.2.1. Asymmetric Mappings

3.2.1.1. Message/External-Body

 This is mapped into a mime-body-part, as specified in [4].

3.2.1.2. Message/Partial

 This is mapped onto a message, and the following heading extension is
 used.  The extension is derived from the message/partial parameters:
                partial-message  HEADING-EXTENSION
                    VALUE PartialMessage
                    ::= id-hex-partial-message
                PartialMessage ::=
                    SEQUENCE {
                        number INTEGER,
                        total  INTEGER,
                        id     IA5String
                    }
 If this heading is present when mapping from MHS to MIME, then a
 message/partial should be generated.

3.2.1.3. Nested Multipart Content-types

 In MIME, a multipart content refers to a set of content-types, not a
 message with a set of content-types. However, a nested multipart
 content will always be mapped to an IPMS.MessageBodyPart, with an
 IPMS.BodyPart for each contained content-type.
 The only mandatory field in the heading is the IPMS.this-IPM, which
 must always be generated (by the gateway). A IPMS.subject field
 should also be generated where there is no "real" heading. This will
 present useful information to the non-MIME capable X.400(88) and to
 all X.400(84) UAs.

Alvestrand, Kille, Miles, Rose & Thompson [Page 6] RFC 1495 MHS/RFC-822 Message Body Mapping August 1993

 The IPM.subject fields for the various types are:
 mixed:        "Multipart Message"
 alternative:  "Alternate Body Parts containing the same information"
 digest:       "Message Digest"
 parallel:     "Body Parts to be interpreted in parallel"

3.2.2. Multipart IPMS Heading Extension

 The following IPMS.HeadingExtension should be generated for all
 multipart content-types, with the enumerated value set according to
 the subtype:
                multipart-message HEADING-EXTENSION
                    VALUE MultipartType
                    ::= id-hex-multipart-message
                MultipartType ::=
                    ENUMERATED {
                        mixed(1),
                        alternative(2),
                        digest(3),
                        parallel(4)
                    }
 If this heading is present when mapping from MHS to MIME, then the
 appropriate multipart content-type should be generated.

4. Mapping between X.400 and RFC-822 Message Headers

 Replace the first paragraph of Section 3.3.4 on page 26 of RFC-1327
 to read as:
      In cases where T.61 strings are used only for conveying human-
      interpreted information, the aim of this mapping is to render
      the characters appropriately in the remote character set, rather
      than to maximize reversibility.  For these cases, the following
      steps are followed to find an appropriate encoding:
      1) If all the characters in the string are contained within the
      ASCII repertoire, the string is simply copied.
      2) If all the characters in the string are from an IANA-
      registered character set, then the appropriate encoded-word(s)
      according to [5] are generated instead.
      3) If the characters in the string are from a character set
      which is not registered with the IANA, then the mappings to IA5
      defined in CCITT Recommendation X.408 (1988) shall be used

Alvestrand, Kille, Miles, Rose & Thompson [Page 7] RFC 1495 MHS/RFC-822 Message Body Mapping August 1993

      [CCITT/ISO88a].  These will then be encoded in ASCII.
      This approach will only be used for human-readable information
      (Subject and FreeForm Name).
      When mapping from an RFC-822 header, when an encoded-word (as
      defined in [5]) is encountered:
      1) If all the characters contained therein are mappable to T.61,
      the string content shall be converted into T.61.
      2) Otherwise, the encoded-word shall be copied directly into the
      T.61 string.
 Modify procedure "2a" on page 56 of RFC-1327 to read as:
      If the IPMS.ORDescriptor.free-form-name is present, convert it
      to ASCII or T.61 (Section 3.3.4), and use this as the 822.phrase
      component of the 822.mailbox construct.
 Modify the final paragraph of procedure "2" on page 55 of RFC-1327 to
 read as:
      The string is then encoded into T.61 or ASCII using a human-
      oriented mapping (as described in Section 3.3.4).  If the string
      is not null, it is assigned to IPMS.ORDescriptor.free-form.name.
 Modify the second paragraph of procedure "3" on page 55 of RFC-1327
 to read as:
      If the 822.group construct is present, any included 822.mailbox
      is encoded as above to generate a separate IPMS.ORDescriptor.
      The 822.group is mapped to T.61 or ASCII (as described in
      Section 3.3.4), and an IPMS.ORDescriptor with only an free-
      form-name component is built from it.
 Modify procedure "822.Subject" on page 62 of RFC-1327 to read as:
      Mapped to IMPS.Heading.subject.  The field-body uses the human-
      oriented mapping referenceed in Section 3.3.4.
 Modify procedure "IPMS.Heading.subject" on page 71 of RFC-1327 to
 read as:
      Mapped to "Subject:".  The contents are converted to ASCII or
      T.61 (Section 3.3.4).  Any CRLF are not mapped, but are used as
      points at which the subject field must be folded.

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5. OID Assignments

 MIME-MHS DEFINITIONS ::= BEGIN
 mail OBJECT IDENTIFIER ::= { internet 7 }
 mime-mhs OBJECT IDENTIFIER ::= { mail 1 }
 mime-mhs-headings OBJECT IDENTIFIER ::= { mime-mhs 1 }
 id-hex-partial-message OBJECT IDENTIFIER ::=
         { mime-mhs-headings 1 }
 id-hex-multipart-message OBJECT IDENTIFIER ::=
         { mime-mhs-headings 2 }
 mime-mhs-bodies OBJECT IDENTIFIER ::= { mime-mhs 2 }
 END

6. Security Considerations

 There are no explicit security provisions in this document.  However,
 a warning is in order.  This document maps two mechanisms between
 RFC822 and X.400 that could cause problems.  The first is the
 transfer of binary files.  The inherent risks are well known and
 won't be reiterated here.  The second is the propagation of strong
 content typing.  The typing can be used to automatically "launch" or
 initiate applications against those contents.  Any such launching
 leaves the invoker vulnerable to application-specific viruses; for
 example, a spreadsheet macro or Postscript command that deletes
 files.  See [2], Section 7.4.2 for a Postscript-specific discussion
 of this issue.

Alvestrand, Kille, Miles, Rose & Thompson [Page 9] RFC 1495 MHS/RFC-822 Message Body Mapping August 1993

7. Authors' Addresses

 Harald Tveit Alvestrand
 SINTEF DELAB
 N-7034 Trondheim
 NORWAY
 EMail: Harald.Alvestrand@delab.sintef.no
 Steve Kille
 ISODE Consortium
 P.O. Box 505
 London
 SW11 1DX
 England
 Phone: +44-71-223-4062
 EMail: S.Kille@ISODE.COM
 Robert S. Miles
 Soft*Switch, Inc.
 640 Lee Road
 Wayne, PA 19087
 Phone: (215) 640-7556
 EMail: rsm@spyder.ssw.com
 Marshall T. Rose
 Dover Beach Consulting, Inc.
 420 Whisman Court
 Mountain View, CA  94043-2186
 US
 Phone: +1 415 968 1052
 Fax:   +1 415 968 2510
 EMail: mrose@dbc.mtview.ca.us
 Steven J. Thompson
 Soft*Switch, Inc.
 640 Lee Road
 Wayne, PA 19087
 Phone: (215) 640-7556
 EMail: sjt@gateway.ssw.com

Alvestrand, Kille, Miles, Rose & Thompson [Page 10] RFC 1495 MHS/RFC-822 Message Body Mapping August 1993

8. References

 [1] Crocker, D., "Standard for the Format of ARPA Internet Text
     Messages", STD 11, RFC 822, UDEL, August 1982.
 [2] Borenstein, N., and N. Freed, "MIME: Mechanisms for Specifying
     and Describing the Format of Internet Message Bodies", RFC 1341,
     Bellcore, Innosoft, June 1992.
 [3] Hardcastle-Kille, S., "Mapping between X.400(1988) / ISO 10021
     and RFC-822", RFC 1327, University College London, May 1992.
 [4] Alvestrand, H., and S. Thompson, "Equivalences between 1988 X.400
     and RFC-822 Message Bodies", RFC 1494, SINTEF DELAB, Soft*Switch,
     Inc., August 1993.
 [5] Moore, K., "Representation of Non-ASCII Text in Internet Message
     Headers Message Bodies", RFC 1342, University of Tennesse, June
     1992.

Alvestrand, Kille, Miles, Rose & Thompson [Page 11]

/data/webs/external/dokuwiki/data/pages/rfc/rfc1495.txt · Last modified: 1993/08/24 22:52 (external edit)