RFC1137

Network Working Group S. Kille Request for Comments: 1137 University College London Updates: RFC 976 December 1989

            Mapping Between Full RFC 822 and RFC 822 with
                         Restricted Encoding

Status of this Memo

  This RFC suggests an electronic mail protocol mapping for the
  Internet community and UK Academic Community, and requests discussion
  and suggestions for improvements.  This memo does not specify an
  Internet standard.  Distribution of this memo is unlimited.

  This document describes a set of address mappings which will enable
  interworking between systems operating RFC 822 protocols in a general
  manner, and those environments where transfer of RFC 822 messages
  restricts the character set which can be used in addresses.  UUCP
  transfer of RFC 822 messages is an important case of this
  [Crocker82a, Horton86a].

Specification

  This document specifies a mapping between two protocols.  This
  specification should be used when this mapping is performed on the
  Internet or in the UK Academic Community. This specification may be
  modified in the light of implementation experience, but no
  substantial changes are expected.

1. Introduction

  Some mail networks which use RFC 822 cannot support the full
  character set required by all aspects of RFC 822.  This document
  describes a symmetrical mapping between full RFC 822 addressing, and
  a form for use on these networks.  Any addresses within the networks
  will not use the full RFC 822 addressing, and so any addresses
  encoded according to this standard will always represent remote
  addresses.  This document derives from a mapping originally specified
  in RFC 987 [Kille86a], where the domain of application was more
  restricted.  Two terms are now defined:

  Full RFC 822

     This implies full support for transfer to and from any legal RFC
     822 address.  In particular, the quoted-string form of local-part
     must be supported (e.g., <"Joe Soap"@foo.bar>).

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RFC 1137 E-Mail Address and Quoted Strings December 1989

  Restricted RFC 822

     This implies a subset of RFC 822 addressing.  The quoted-string
     form of local-part need not be supported.  Standard UUCP mail
     transfer falls into this category.  Restricted RFC 822 is
     undesirable, but in practice it exists in many places.

     When a message is transferred from full RFC 822 to restricted RFC
     822, and address forms used in full RFC 822 are involved, message
     loss may occur (e.g., it may not be possible to return an error
     message).  This RFC describes a quoting mechanism which may be
     used to map between full RFC 822 and restricted RFC 822, in order
     to alleviate this problem.

2. Encoding

  The RFC 822 EBNF meta notation is used.  Any EBNF definitions taken
  from RFC 822 are prefixed by the string "822.".

  The following EBNF is specified.

     atom-encoded    = *( a-char / a-encoded-char )
     a-char          = <any CHAR except specials (other than "@"
                             and "."), SPACE,
                             CTL, "_", and "#">
     a-encoded-char  = "_"                   ; (space)
                     / "#u#"                 ; (_)
                     / "#l#"                 ; <(>
                     / "#r#"                 ; <)>
                     / "#m#"                 ; (,)
                     / "#c#"                 ; (:)
                     / "#b#"                 ; (\)
                     / "#h#"                 ; (#)
                     / "#e#"                 ; (=)
                     / "#s#"                 ; (/)
                     / "#" 3DIGIT "#"

  The 822.3DIGIT in EBNF.a-encoded-char must have range 0-127, and is
  interpreted in decimal as the corresponding ASCII character.  The
  choice of special abbreviations (as opposed to decimal encoding)
  provided is based on the manner in which this mapping is most
  frequently used.  There are special encodings for each of the
  PrintableString characters not in EBNF.a-char, except ".".  Space is
  given a single character encoding, due to its (expected) frequency of
  use, and backslash as the RFC 822 single quote character.

  This mapping is used to transform between the two forms of 822.word:
  822.quoted-string (restricted RFC 822) and 822.atom (restricted RFC

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RFC 1137 E-Mail Address and Quoted Strings December 1989

  822).  To encode (full RFC 822 -> restricted RFC 822), first remove
  any quoting from any 822.quoted-string.  Then, all EBNF.a-char are
  used directly and all other CHAR are encoded as EBNF.a-encoded-char.

  To decode (restricted RFC 822 -> full RFC 822): if the address can be
  parsed as EBNF.encoded-atom reverse the previous mapping.  If it
  cannot be so parsed, map the characters directly.

3. Application

  This mapping should be used for all addresses, at the MTS or Header
  level.  It is applied to the 822.local-part of the addresses.  For
  example:

     Full RFC 822                       Restricted RFC 822

     [email protected]     <->   [email protected]
     "Steve Kille"@cs.ucl.ac.uk   <->   [email protected]
     "argle#~"@blargle            <->   argle#h##126#@blargle

References

  [Crocker82a]  Crocker, D., "Standard of the Format of ARPA Internet
  Text Messages", RFC 822, August 1982.

  [Horton86a]  Horton, M., "UUCP Mail Interchange Format Standard",
  RFC 976, February 1986.

  [Kille86a]  Kille, S., "Mapping Between X.400 and RFC 822",
  UK Academic Community Report (MG.19), RFC 987, June 1986.

Security Considerations

  Security issues are not discussed in this memo.

Author's Address

  Steve Kille
  University College London
  Gower Street
  WC1E 6BT
  England

  Phone: +44-1-380-7294

  EMail: [email protected]

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