doc/rfc-ja/rfc1428-ja.rfcja

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  <!ENTITY rfc.number "1428">
  <!ENTITY ja.agent "$BBeM}<T(B">
  <!ENTITY ja.body "$BK\BN(B">
  <!ENTITY ja.downgrade "$B3J2<$2(B">
  <!ENTITY ja.outofband "out of band">
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<rfc number="&rfc.number;" category="info"
   xmlns:myns="mailto:julian.reschke@greenbytes.de?subject=rcf2629.xslt"
   xmlns:ja="http://suika.fam.cx/~wakaba/lang/rfc/translation/"
   xmlns:h="http://www.w3.org/1999/xhtml">
<front>
<title abbrev="Transition to 8bit-SMTP/MIME">Transition of Internet Mail from Just-Send-8 to 8bit-SMTP/MIME</title>
<ja:title xml:lang="ja" abbrev="8$B%S%C%H(B SMTP/MIME $B$X$NJQ49(B">Internet $B%a%$%k$N(B8$B$^$s$^Aw$j$+$i(B8$B%S%C%H(B SMTP/MIME $B$X$NJQ49(B</ja:title>
<author initials="G." surname="Vaudreuil" fullname="Greg Vaudreuil">
  <organization abbrev="CNRI">Corporation for National Research Initiatives</organization>
   <address>
     <postal><street>1895 Preston White Drive, Suite 100</street>
     <city>Reston</city><!--, --><region>VA</region> <code>22091</code> 
     <country ja:text="USA">US</country>
     </postal>
     <phone ja:text="(703) 620-8990">+1 703 620 8990</phone>
     <email>GVaudre@CNRI.Reston.VA.US</email>
   </address>
</author>
<date month="February" year="1993" />
<workgroup>SMTP Extensions Working Group</workgroup>
<abstract>
  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      Protocols for extending SMTP to pass 8bit characters have been
      defined <xref target="refs.RFC1425" /> <xref target="refs.RFC1426" />.
      These protocols require that messages transported by
      the extended SMTP are to be encoded in MIME 
      <xref target="refs.RFC1341" /> <xref target="refs.RFC1342" />. 
      Before work began on these protocols, several SMTP implementations 
      adopted ad-hoc mechanisms for sending 8bit data. It is desirable 
      for the extended SMTP environment and these ad hoc mechanisms 
      interoperate.  This document outlines the problems in this 
      environment and an approach to minimizing the cost of transition 
      from current usage of non-MIME 8bit messages to MIME.
    </ja:l>
    <ja:l xml:lang="ja">
      8$B%S%C%HJ8;z$rDL2a$5$;$k$h$&$K(B SMTP 
      $B$r3HD%$9$k(B&ja.protocol;$B$,Dj5A$5$l$F$$$^$9(B
      <xref target="refs.RFC1425" /> <xref target="refs.RFC1426" />$B!#(B
      $B$3$l$i$N(B&ja.protocol;$B$G$O!"3HD%(B SMTP $B$GE>Aw$5$l$k%a%C%;!<%8$,(B
      MIME <xref target="refs.RFC1341" /> <xref target="refs.RFC1342" />
      $B$GId9f2=$5$l$F$$$k$3$H$,I,MW$G$9!#$3$l$i$N(B&ja.protocol;$B$N:n6H$,;O$^$k0JA0!"4v$D$+$N(B
      SMTP $B<BAu$O(B8$B%S%C%H!&%G!<%?$rAw?.$9$k$?$a$NFC@_5!9=$r:NMQ$7$F$$$^$7$?!#3HD%(B
      SMTP $B4D6-$H$3$NMM$JFC@_5!9=$,6(D4$7$FF/$/$3$H$,K>$^$7$$$G$9!#$3$NJ8=q$O!"$3$l$i$N4D6-$G$NLdBj$H!"Hs(B MIME 8$B%S%C%H!&%a%C%;!<%8$N8=:_$NMxMQK!$+$i(B
      MIME $B$X$NJQ49$N7PHq$N:G>.2=$NJ}K!$K$D$$$F35@b$7$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>
</abstract>
</front>
<ja:front>
<author fullname="$B$o$+$P(B" ja:id="wakaba">
        <address>
        <email>w@suika.fam.cx</email>
        <uri>http://suika.fam.cx/~wakaba/</uri>
        </address>
</author>
<ja:copyright>
  <ja:item>Copyright &#xa9; $B$o$+$P(B (2002)$B!#A48"J]N1!#(B</ja:item>
</ja:copyright>
<ja:change>
  <ja:item year="2002" month="05" day="08"><author ja:ref="wakaba" />
    <t><ja:link type="rfc" number="2629" /> $B$G%^!<%/IU$1!#(B</t>
    <t>$BK]Lu40N;!#(B</t>
  </ja:item>
</ja:change><!-- $Date: 2002/05/08 14:43:57 $ -->
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</ja:front>
<middle>

<section title="Terminology" ja:title-ja="$BMQ8l(B"><!-- 1. -->
  <t>
    <ja:pair>
    <ja:l xml:lang="en">
   RFC 821 defines a 7bit transport.  A transport agent which does not
   clear the high order bit upon receipt of octets with this bit set in
   SMTP messages is called 8 bit transparent in this document. An
   implementation of the general SMTP Extensions document 
      <xref target="refs.RFC1425" /> and the
      8bit extensions protocol <xref target="refs.RFC1426" /> 
      which passes MIME messages using all 8
   bits of an octet is called 8bit ESMTP.  An implementation of extended
   SMTP which does not accept 8bit characters is called 7bit ESMTP.  A
   gateway is defined to be a transport agent with User Agent authority
      to alter or convert the content of a message.
    </ja:l>
    <ja:l xml:lang="ja">
      <ja:link type="rfc" number="821" /> $B$O(B8$B%S%C%HE>Aw$rDj5A$7$F$$$^$9!#(B
      SMTP $B%a%C%;!<%8Cf$N<u$1<h$C$?%*%/%F%C%H$N:G>e0L%S%C%H$r!"$3$N%S%C%H$KCM$r@_Dj$9$k$3$H$G>C5n$7$J$$E>Aw(B&ja.agent;$B$r!"$3$NJ8=q$G$O(B8$B%S%C%HF)2a$H8F$S$^$9!#0lHL(B 
      SMTP $B3HD%J8=q(B <xref target="refs.RFC1425" /> $B5Z$S(B
      MIME $B%a%C%;!<%8$r%*%/%F%C%H$N(B8$B%S%C%HA4$F$r;H$C$FEO$9(B8$B%S%C%H3HD%(B&ja.protocol; 
      <xref target="refs.RFC1426" /> $B$N<BAu$r(B8$B%S%C%H(B 
      ESMTP $B$H8F$S$^$9!#(B8$B%S%C%HJ8;z$r<u$1IU$1$J$$3HD%(B SMTP 
      $B$N<BAu$r(B7$B%S%C%H(B ESMTP $B$H8F$S$^$9!#4XLg(B (gateway) 
      $B$O!"%a%C%;!<%8$NFbMF$rJQ$($k!&JQ49$9$k(B&ja.UserAgent;$BEv6I$D$-E>Aw(B&ja.agent;$B$HDj5A$7$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>
</section>

<section title="The Problem" ja:title-ja="$BLdBjE@(B"><!-- 2. -->
  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      SMTP as defined in RFC 821 limits the sending of Internet Mail to
      US-ASCII <xref target="refs.ASCII" /> characters.  As the Internet 
      has grown to include non-English correspondents, the need to 
      communicate with character sets
      other than US-ASCII has prompted many vendors and users to extend
      SMTP or RFC 822 to use non-ASCII character sets.  Common approaches
      are to send 7 bit national variant ISO 646 character sets over
      current RFC822/SMTP, to extend SMTP and RFC822 to use 8bit ISO 8859
      character sets, and to use proprietary PC character sets.
    </ja:l>
    <ja:l xml:lang="ja">
      <ja:link type="rfc" number="821" /> $B$GDj5A$5$l$?(B SMTP $B$O(B
      Internet $B%a%$%k$NAw?.$r(B US-ASCII <xref target="refs.ASCII" />
      $BJ8;z$K@)8B$7$F$$$^$7$?!#(B Internet 
      $B$,Hs1Q8lJ8DL<T$r4^$`MM$K@.D9$9$k$K=>$$!"Hs(B US-ASCII 
      $BJ8;z=89g$K$h$k0U;WABDL$NI,MW@-$+$i!"B?$/$N@=B$<T$dMxMQ<T$,(B SMTP 
      $B$d(B <ja:link type="rfc" number="822" /> $B$rHs(B ASCII 
      $BJ8;z=89g$r;HMQ$9$k$h$&$K3HD%$7$h$&$H$7$^$7$?!#$=$N6&DL$N<jCJ$K$O(B7$B%S%C%H$N9q2HHG(B
      ISO 646 $BJ8;z=89g$r8=9T$N(B RFC 822/SMTP $B$GAw?.$9$k(B, SMTP $B$H(B
      RFC822 $B$r(B8$B%S%C%H$N(B ISO 8859 $BJ8;z=89g$r;HMQ$9$k$h$&$K3HD%$9$k(B,
      $BFH@j(B PC $BJ8;z=89g$r;HMQ$9$k(B, $B$,$"$j$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>

  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      A third approach is used for Japanese mail.  Japanese characters are
   represented by pairs of octets with the high order bit cleared.
   Switching between 14 bit character sets and 7 bit character sets is
   indicated within the message by ISO 2022 escape sequences.
    </ja:l>
    <ja:l xml:lang="ja">
      $B;0HVL\$NJ}K!$OF|K\8l%a%$%k$K;H$o$l$F$$$^$9!#F|K\8lJ8;z$O:G>e0L%S%C%H$,>C5n$5$l$?%*%/%F%C%H$NAH9g$;$GI=8=$7$^$9!#(B14$B%S%C%HJ8;z=89g$H(B7$B%S%C%HJ8;z=89g$O%a%C%;!<%8Cf$G$O(B
      ISO 2022 $B%(%9%1!<%WNs$G@Z$jBX$($^$9!#(B
    </ja:l>
    </ja:pair>
  </t>
  <ja:note>
    <t>$B;0HVL\$NJ}K!$H$O!VFH@j(B PC $BJ8;z=89g$N;HMQ!W$G$9$+$i!"$3$N@bL@$G$O9gCW$7$^$;$s!#$*$=$i$/!";0HVL\$NJ}K!$O!"!V0lHVL\!&FsHVL\0J30$NJ}K!!W$H$G$b$7$?$+$C$?$N$G$7$g$&!#(B</t>
  </ja:note>

  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      So long as these implementations can communicate without intermediate
   transformations and have a loose private agreement on the use of a
   specific character set without tagging, basic mail service can be
   provided.
    </ja:l>
    <ja:l xml:lang="ja">
      $B$3$l$i$N<BAu$OESCf7PO)$G$NJQ7AL5$7$KDL?.=PMh!"FCDjJ8;z=89g$N;%L5$7$G$N;HMQ$N4K$$;dE*$J9g0U$,$"$k$N$G!"4pK\E*$J%a%$%k!&%5!<%S%9$,Ds6!=PMh$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>
  
  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      In the transition to the negotiated 8bit ESMTP/MIME environment, it
   is important that mail sent by a currently non-conforming user can be
   read by another non-conforming user.  This existing functionality is
   reduced by conversion from 8bit text to text encoded in unreadable
   Base-64 or "garbled" text encoded in quoted printable.
    </ja:l>
    <ja:l xml:lang="ja">
      $B@^>W(B8$B%S%C%H(B ESMTP/MIME 
      $B4D6-$X$NJQ49$G!"8=:_HsE,9g$NMxMQ<T$,Aw?.$7$?%a%$%k$OB>$NHsE,9g$NMxMQ<T$,FI$`$3$H$,=PMh$k$3$H$O=EMW$G$9!#$3$N4{B85!G=@-$O!"(B8$B%S%C%HJ8$+$iIT2DFI(B
      Base-64 $B$GId9f2=$5$l$?J8$d(B quoted printable 
      $B$GId9f2=$5$l$?!VJ8;z2=$1$7$?!WJ8$KJQ49$9$k$3$H$G8:>/$7$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>
  
  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      There are several interesting non-interoperable cases that currently
      exist in non US-ASCII mail and several new ones likely to emerge in a
      transition to 8bit/MIME.  Below is a listing of the 
      transition-to-mime cases.  Only solutions to <xref target="s2.i4" /> 
      in the context of a translating gateway are discussed in this memo.
    </ja:l>
    <ja:l xml:lang="ja">
      $B8=:_Hs(B US-ASCII $B%a%$%k$KB8:_$9$k6=L#?<$$Aj8_DL?.IT2D$J;vNc!"$"$k$$$O(B8$B%S%C%H(B/MIME 
      $B$X$NJQ49$GIb>e$7$=$&$J?7$7$$;vNc$,4v$D$+$"$j$^$9!#2<$K5s$2$k$N$O!"(B
      MIME $B$X$NJQ49$N;vNc$G$9!#JQ494XLg$K$*$1$k(B <xref target="s2.i4" />
      $B$N2r7h:v$N$_$r$3$N%a%b$G$O<h$j>e$2$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>
  
  <figure>
    <ja:pair>
    <ja:l xml:lang="en">
      <ja:artwork>
        <artwork>
                \ Receiver
                  \    7bit     8bit          MIME/
             Sender \| only   | transparent | ESMTP
           ----------------------------------------
           7bit only |  (1)   |    (1)      | (1)
           ----------------------------------------
    8bit transparent |  (2)   |    (3)      | (4)
           ----------------------------------------
          MIME/ESMTP |  (5)   |    (5)      | (6)
</artwork>
        <h:table>
          <h:thead>
            <h:tr>
              <h:th class="css-first-child">Sender\Receiver</h:th>
              <h:th>7bit only</h:th>
              <h:th>8bit transparent</h:th><h:th>MIME/ESMTP</h:th>
            </h:tr>
          </h:thead>
          <h:tbody>
            <h:tr>
              <h:th>7bit only</h:th>
              <h:td><xref target="s2.i1" /></h:td>
              <h:td><xref target="s2.i1" /></h:td>
              <h:td><xref target="s2.i1" /></h:td>
            </h:tr>
            <h:tr>
              <h:th>8bit transparent</h:th>
              <h:td><xref target="s2.i2" /></h:td>
              <h:td><xref target="s2.i3" /></h:td>
              <h:td><xref target="s2.i4" /></h:td>
            </h:tr>
            <h:tr>
              <h:th>MIME/ESMTP</h:th>
              <h:td><xref target="s2.i5" /></h:td>
              <h:td><xref target="s2.i5" /></h:td>
              <h:td><xref target="s2.i6" /></h:td>
            </h:tr>
          </h:tbody>
        </h:table>
      </ja:artwork>
    </ja:l>
    <ja:l xml:lang="ja">
      <ja:artwork>
        <h:table>
          <h:thead>
            <h:tr>
              <h:th class="css-first-child">$BAw?.<T(B\$B<u?.<T(B</h:th>
              <h:th>7$B%S%C%H$N$_(B</h:th>
              <h:th>8$B%S%C%HF)2a(B</h:th><h:th>MIME/ESMTP</h:th>
            </h:tr>
          </h:thead>
          <h:tbody>
            <h:tr>
              <h:th>7$B%S%C%H$N$_(B</h:th>
              <h:td><xref target="s2.i1" /></h:td>
              <h:td><xref target="s2.i1" /></h:td>
              <h:td><xref target="s2.i1" /></h:td>
            </h:tr>
            <h:tr>
              <h:th>8$B%S%C%HF)2a(B</h:th>
              <h:td><xref target="s2.i2" /></h:td>
              <h:td><xref target="s2.i3" /></h:td>
              <h:td><xref target="s2.i4" /></h:td>
            </h:tr>
            <h:tr>
              <h:th>MIME/ESMTP</h:th>
              <h:td><xref target="s2.i5" /></h:td>
              <h:td><xref target="s2.i5" /></h:td>
              <h:td><xref target="s2.i6" /></h:td>
            </h:tr>
          </h:tbody>
        </h:table>
      </ja:artwork>
    </ja:l>
    </ja:pair>
  </figure>

  <list style="hanging">
    <t hangText="(1)" ja:anchor="s2.i1">
      <ja:pair>
      <ja:l xml:lang="en">7Bit non-MIME sender to 7bit, MIME, or 
      8bit transparent receiver</ja:l>
      <ja:l xml:lang="ja">7$B%S%C%HHs(B MIME $BAw?.<T$+$i(B7$B%S%C%H$^$?$O(B 
      MIME, 8$B%S%C%HF)2a<u?.<T$X(B</ja:l>
      </ja:pair>
        <vspace breakLines="1" />
      <ja:pair>
      <ja:l xml:lang="en">
      This will continue to work unchanged with nationally varient ISO
      646 or ISO 2022 character set shifting if an external "out of
      band" agreement exists between the sender and the receiver.  A
      7bit to 8bit/ESMTP gateway need not alter the content of this
      message.
      </ja:l>
      <ja:l xml:lang="ja">
        ISO 646 $B9q2HHG$d(B ISO 2022 $BJ8;z=89gE>0\$r!"30It!V(B&ja.outofband;$B!W9g0U$,Aw<u?.<T4V$GB8:_$9$k>l9g$OJQ99L5$/1?MQ$7B3$1$^$9!#(B7$B%S%C%H$+$i(B8$B%S%C%H(B/SMTP 
        $B$X$N4XLg$O$3$N%a%C%;!<%8$NFbMF$rJQ$($kI,MW$O$"$j$^$;$s!#(B
      </ja:l>
      </ja:pair>
    </t>
    <ja:note>
      <t>Jargon File $B$K$O!"(B $B!V(Bout of band$B!W(B = 
      <h:q title="Jargon File $B$+$i!V(Bout of band$B!W(B" xml:lang="en">sometimes
      used to describe what communications people call $B!F(Bshift characters$B!G(B,
      such as the <h:code>ESC</h:code> that leads control sequences for 
      many terminals</h:q> $B$H=q$+$l$F$$$^$9!#(B</t>
    </ja:note>

    <t hangText="(2)" ja:anchor="s2.i2">
      <ja:pair>
      <ja:l xml:lang="en">8bit sender to 7bit non-MIME receiver</ja:l>
      <ja:l xml:lang="ja">8$B%S%C%HAw?.<T$+$i(B7$B%S%C%HHs(B MIME $B<u?.<T$X(B</ja:l>
      </ja:pair>
        <vspace breakLines="1" />
      <ja:pair>
      <ja:l xml:lang="en">
        The receiver will receive bit-stripped mail which results in the
      mis-interpretation of the data and the wrong character being
      displayed or printed.  Mail sent using languages where most
      characters are in the US-ASCII subset of ISO 8859 may be somewhat
      readable.
      </ja:l>
      <ja:l xml:lang="ja">
        $B<u?.<T$O!"%G!<%?$N8m2r<a$N7k2L$?$k%S%C%HMn$A%a%$%k$r<u$1<h$j!"4V0c$C$?J8;z$,I=<(!&0u:~$5$l$k$3$H$K$J$k$G$7$g$&!#$[$H$s$I$NJ8;z$,(B 
        ISO 8859 $B$N(B US-ASCII $BItJ,=89gCf$K$"$k8@8l$r;H$C$FAw$i$l$?%a%$%k$O$=$l$J$j$KFI$a$k$+$b$7$l$^$;$s!#(B
      </ja:l>
      </ja:pair>
    </t>

    <t hangText="(3)" ja:anchor="s2.i3">
      <ja:pair>
      <ja:l xml:lang="en">8bit transparent sender to 8bit transparent receiver</ja:l>
      <ja:l xml:lang="ja">8$B%S%C%HF)2aAw?.<T$+$i(B8$B%S%C%HF)2a<u?.<T$X(B</ja:l>
      </ja:pair>
        <vspace breakLines="1" />
      <ja:pair>
      <ja:l xml:lang="en">
        Will work if an external agreement "out of band" to use a
      particular character set without tagging exists between the sender
      and the receiver.
      </ja:l>
      <ja:l xml:lang="ja">
        $BFCDjJ8;z=89g$r;%L5$7$G;HMQ$9$k30It9g0U!V(B&ja.outofband;$B!W$,Aw<u?.4V$KB8:_$9$k>l9g$O$&$^$/F/$/$G$7$g$&!#(B
      </ja:l>
      </ja:pair>
    </t>

    <t hangText="(4)" ja:anchor="s2.i4">
      <ja:pair>
      <ja:l xml:lang="en">8bit transparent sender to MIME/ESMTP conformant receiver</ja:l>
      <ja:l xml:lang="ja">8$B%S%C%HF)2aAw?.<T$+$i(B MIME/ESMTP $BE,9g<u?.<T$X(B</ja:l>
      </ja:pair>
        <vspace breakLines="1" />
      <ja:pair>
      <ja:l xml:lang="en">
        Will work if a reasonable upgrade path is provided via gateways,
      the indicated character set tag inserted by the gateway is correct
      and the receiver supports the character set chosen by the sender.
      This case is the focus of this memo.
      </ja:l>
      <ja:l xml:lang="ja">
        $BJ,JL$"$k3J>e$27PO)$,4XLg7PM3$GDs6!$5$l$F$$$F!"4XLg$,A^F~$9$kJ8;z=89g;%$,@5$7$/$F!"<u?.<T$,Aw?.<T$NA*$s$@J8;z=89g$KBP1~$7$F$$$l$P!"$&$^$/F/$-$^$7$g$&!#$3$N>l9g$,$3$N%a%b$N>GE@$G$9!#(B
      </ja:l>
      </ja:pair>
    </t>

    <t hangText="(5)" ja:anchor="s2.i5">
      <ja:pair>
      <ja:l xml:lang="en">MIME/ESMTP sender to non-MIME 7bit receiver</ja:l>
      <ja:l xml:lang="ja">MIME/ESMTP $BAw?.<T$+$iHs(B MIME 7$B%S%C%H<u?.<T$X(B</ja:l>
      </ja:pair>
        <vspace breakLines="1" />
      <ja:pair>
      <ja:l xml:lang="en">
        Because the ESMTP/MIME sender cannot know if the receiver will
      understand 8bits, the sender will encode the text into base-64 or
      quoted-printable which may be considered "garbled" by the
      receiver.  To provide a useful downgrade path the gateway must
      have some knowledge about the capabilities of the receiver. When
      the character set can be clearly identified, techniques like the
      menmonic MNEM encoding described in RFC 1345 may be helpful in
      this case.
      </ja:l>
      <ja:l xml:lang="ja">
        ESMTP/MIME $BAw?.<T$O<u?.<T$,(B8$B%S%C%H$rM}2r$9$k$+$I$&$+CN$jF@$J$$$N$G!"Aw?.<T$OJ8$r(B 
        base-64 $B$+<u?.<T$K!VJ8;z2=$1$7$?!W$H;W$o$l$k$+$b$7$l$J$$(B 
        quoted-printable $B$GId9f2=$9$k$G$7$g$&!#M-MQ$J3J2<$27PO)$rDs6!$9$k$K$O4XLg$O<u?.<T$NM}2rG=NO$K$D$$$F$NCN<1$rM-$9$kI,MW$,$"$j$^$9!#J8;z=89g$,L@3N$K<1JL=PMh$k;~$O!"(B 
        <ja:link type="rfc" number="1345" /> $B$G@bL@$5$l$F$$$k5-K!(B MNEM 
        $BId9f2=$NMM$J<jK!$,$3$N>l9g$K$OM-MQ$+$b$7$l$^$;$s!#(B
      </ja:l>
      </ja:pair>
    </t>

    <t hangText="(6)" ja:anchor="s2.i6">
      <ja:pair>
      <ja:l xml:lang="en">MIME/ESMTP sender to MIME/ESMTP receiver</ja:l>
      <ja:l xml:lang="ja">MIME/ESMTP $BAw?.<T$+$i(B MIME/ESMTP $B<u?.<T$X(B</ja:l>
      </ja:pair>
        <vspace breakLines="1" />
      <ja:pair>
      <ja:l xml:lang="en">
        Interoperability will be attained provided the receiver supports
      the character set chosen by the sender.
      </ja:l>
      <ja:l xml:lang="ja">$BAj8_DL?.@-$OAw?.<T$,A*Br$7$?J8;z=89g$K<u?.<T$,BP1~$9$k$3$H$K$h$jK~$?$5$l$^$9!#(B</ja:l>
      </ja:pair>
    </t>
  </list>
</section>

<section title="Upgrade Path from 8bit Transparent to ESMTP/MIME"
 ja:title-ja="8$B%S%C%HF)2a$+$i(B ESMTP/MIME $B$X$N(B&ja.upgrade;$B7PO)(B"><!-- 3. -->

  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      A gateway which has been upgraded to support Extended SMTP may
   upgrade an 8bit message received to MIME.  This is consistent with
   the requirement that all 8bit mail sent by ESMTP be encoded in MIME.
   The upgrade should be done using the best available information.
    </ja:l>
    <ja:l xml:lang="ja">
      $B3HD%(B SMTP $B$KBP1~$9$k$h$&(B&ja.upgrade;$B$9$k4XLg$O!"<u?.$7$?(B8$B%S%C%H!&%a%C%;!<%8$r(B
      MIME $B$K(B&ja.upgrade;$B$7$F9=$$$^$;$s!#$3$l$O(B ESMTP $B$GAw?.$5$l$k(B8$B%S%C%H!&%a%$%k$OA4$F(B
      MIME $B$GId9f2=$5$l$F$$$J$1$l$P$J$i$J$$$H$$$&MW7o$rK~$?$7$^$9!#(B&ja.upgrade;$B$O0lHVMxMQ2DG=$J>pJs$r;H$C$F9T$&$Y$-$G$9!#(B
    </ja:l>
    </ja:pair>
  </t>

  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      A site may "upgrade" to MIME en-masse by implementing MIME conversion
   for all messages leaving the site.  For text messages, the body can
   be converted by adding a MIME-version header and a Content-Type:
   Text/Plain with the character set in use in the site, provided the
   site uses a single character set.
    </ja:l>
    <ja:l xml:lang="ja">
      $B%5%$%H$O!"%5%$%H$rN%$l$kA4$F$N%a%C%;!<%8$r!"(B
      MIME $B$r<BAu$9$k$3$H$G$^$H$a$F(B MIME $B$K!V(B&ja.upgrade;$B!W$7$F$b9=$$$^$;$s!#%F%-%9%H!&%a%C%;!<%8$K$D$$$F$O!"(B&ja.body;$B$O(B
      MIME-version $BF,$H(B Content-Type: Text/Plain 
      $B$K%5%$%HFb$G;H$o$l$F$$$kJ8;z=89g$r$D$1$k$3$H$G!"%5%$%H$,C10lJ8;z=89g$r;H$C$F$$$k>l9g$OJQ49=PMh$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>

  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      An appropriate Content-Transfer-Encoding header line must be added to
   indicate any encoding that may be necessary.
    </ja:l>
    <ja:l xml:lang="ja">
      $BE,@Z$J(B Content-Transfer-Encoding 
      $BF,9T$r!"I,MW$+$b$7$l$J$$Id9f2=$r<($9$N$K2C$($J$1$l$P$J$j$^$;$s!#(B
    </ja:l>
    </ja:pair>
  </t>

<!--
    Example:
--><ja:example xml:space="preserve">
MIME-Version: 1.0
Content-Type: Text/Plain; Charset = ISO-8859-1
Content-Transfer-Encoding: 8bit
</ja:example>

  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      If no information about the character set in use is available, the
   gateway should upgrade the content by using the character set
   "unknown-8bit". The unknown-8bit value of the charset parameter
   indicates only that no reliable information about the character
   set(s) used in the message was available.
    </ja:l>
    <ja:l xml:lang="ja">
      $B;HMQ$5$l$F$$$kJ8;z=89g$K$D$$$F$N>pJs$,L5$$>l9g$O!"4XLg$OFbMF$rJ8;z=89g(B 
      "unknown-8bit" $B$r;H$C$F(B&ja.upgrade;$B$9$k$Y$-$G$9!#(B charset
      $B%Q%i%a!<%?!<$N(B unknown-8bit 
      $BCM$O%a%C%;!<%8$K;H$o$l$F$$$kJ8;z=89g$K$D$$$F$N3N<B$J>pJs$rF@$k$3$H$,=PMh$J$+$C$?$3$H$N$_$r<($7$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>

  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      If a message body has been upgraded to MIME, the RFC 822 headers
   containing non US-ASCII characters must be upgraded to conform with
   the header encoding rules of RFC1342. A gateway should recode all
   unstructered header fields as well as RFC 822 "comment"s and
   "phrase"s according to the rules of RFC 1342. There is no equivalent
   in RFC 1342 to the "8bit" Content-Transfer-Encoding value for message
   bodies so all 8bit header text must be transformed according to
   either the "B" or the "Q" encoding method.  For ISO 8859 character
   sets, the "Q" encoding will generally result in somewhat readable
   headers.
    </ja:l>
    <ja:l xml:lang="ja">
      $B%a%C%;!<%8(B&ja.body;$B$,(B MIME $B$K(B&ja.upgrade;$B$5$l$k>l9g!"Hs(B US-ASCII
      $BJ8;z$r4^$`(B <ja:link type="rfc" number="822" /> $BF,$O(B
      RFC1342 $B$NF,Id9f2=5,B'$KE,9g$9$k$h$&(B&ja.upgtade;$B$7$J$1$l$P$J$j$^$;$s!#4XLg$OA4$F$NHs9=B$2=F,NN0h$H(B 
      RFC 822 "comment" $B$H(B "phrase" $B$r(B RFC 1342 
      $B$N5,B'$K=>$$:FId9f2=$9$k$Y$-$G$9!#%a%C%;!<%8(B&ja.body;$B$N(B "8bit" 
      $BFbMFE>AwId9f2=CM$KAjEv$9$k$b$N$O(B RFC 1342 
      $B$K$OL5$$$N$G!"A4$F$N(B8$B%S%C%HF,J8$O(B "B" $BId9f2=J}<0$^$?$O(B "Q"
      $BId9f2=J}<0$GId9f2=$7$J$1$l$P$J$j$^$;$s!#(B ISO 8859 $BJ8;z=89g$K$O!"(B
      "Q" $BId9f2=$r;H$&$H!"DL>o$d$d2DFI$JF,$H$J$j$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>

  <figure>
    <preamble>
      <ja:pair>
      <ja:l xml:lang="en">
        Trace information should be added to the document with a convert
   clause: "rfc822-to-8bit", "rfc822-to-base-64" or "rfc822-to-quoted-
   printable" e.g.,
      </ja:l>
      <ja:l xml:lang="ja">
        $BDI@W>pJs$r<!$NNc$N$h$&$KJQ49(B (convert) $B>r9`(B "rfc822-to-8bit", 
        "rfc822-to-base-64", "rfc822-to-quoted-printable" 
        $B$D$-$GJ8=q$KDI2C$9$k$Y$-$G$9!#(B
      </ja:l>
      </ja:pair>
    </preamble>
    
    <artwork xml:space="preserve">
   Received: from dbc.mtview.ca.us by dbc.mtview.ca.us
             convert rfc822-to-8bit; Tue, 01 Sep 1992 01:18:00 -0700
</artwork>
  </figure>
</section>

<section title="Appendix $B!=(B The $B!H(Bunknown-8bit$B!I(B Character Set"
 ja:title-ja="$BImB0=q(B $B!=(B $B!V(Bunknown-8bit$B!WJ8;z=89g(B" myns:unnumbered="yes">

  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      This section defines a "charset" parameter, for use in a MIME
      Content-Type field.
    </ja:l>
    <ja:l xml:lang="ja">
      $B$3$N@a$G$O(B MIME Content-Type $BNN0h$G;H$&(B "charset" 
      $B%Q%i%a!<%?!<$rDj5A$7$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>

  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      A special purpose character set called "unknown-8bit" is defined to
   be an unknown 8bit character set, encoded into a sequence of octets.
   It can be used as a label for any character set from any language,
   using any encoding.  It must not be further defined.
    </ja:l>
    <ja:l xml:lang="ja">
      "unknown-8bit" $B$H$$$&FC<lL\E*J8;z=89g$r!"%*%/%F%C%HNs$KId9f2=$5$l$?L$CN$N(B8$B%S%C%HJ8;z=89gMQ$KDj5A$7$^$9!#$3$l$O$$$+$J$k8@8l$G$$$+$J$kId9f2=$rMQ$$$k$$$+$J$kJ8;z=89g$K$b;%$H$7$F;H$&$3$H$,=PMh$^$9!#$3$l0J>e$ODj5A$7$^$;$s!#(B
    </ja:l>
    </ja:pair>
  </t>

  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      The use of this token in a "charset=" field of a message indicates
   that nothing is known about the character set used. This marker is
   intended for use by non-MIME to MIME gateways; specifically in those
   which translate from SMTP to 8bit ESMTP/MIME.
    </ja:l>
    <ja:l xml:lang="ja">
      $B$3$N;z6g$r%a%C%;!<%8$N(B "charset=" 
      $BNN0h$G;H$&$3$H$G!";H$o$l$F$$$kJ8;z=89g$K$D$$$FA4$/$b$C$FITL@$G$"$k$3$H$r<($7$^$9!#$3$N0u$OHs(B MIME $B$+$i(B MIME $B$X$N4XLg!"6qBNE*$K$O(B SMTP 
      $B$+$i(B8$B%S%C%H(B ESMTP/MIME $B$KJQ49$9$k4XLg$G;H$&$3$H$r0U?^$7$F$$$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>

  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      This character set is not intended to be used by mail composers.  
      It is assumed that the mail composer knows the character set in 
      use and will mark it with a character set value as specified in 
      <xref target="refs.RFC1341" />, as amended by current Assigned 
      Numbers documents <xref target="refs.STD2" />.
    </ja:l>
    <ja:l xml:lang="ja">
      $B$3$NJ8;z=89g$O%a%$%k:n@.<T$,;H$&$3$H$O0U?^$7$F$$$^$;$s!#%a%$%k:n@.<T$O;HMQ$9$kJ8;z=89g$rCN$C$F$$$F!"(B 
      <xref target="refs.RFC1341" /> $B$G5,Dj$5$l$F8=9T$N3dEvHV9fJ8=q(B 
      <xref target="refs.STD2" /> 
      $B$G2~D{$5$l$?J8;z=89gCM$G0u$r$D$1$k$HA[Dj$7$F$$$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>

  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      The use of the "unknown-8bit" label is intended only by mail gateway
   agents which cannot determine via out-of-band information the
   intended character set.
    </ja:l>
    <ja:l xml:lang="ja">
      "unknown-8bit" $B;%$N;HMQ$O!"(B &ja.outofband;
      $B>pJs$K$h$j0U?^$5$l$?J8;z=89g$r7hDj=PMh$J$$%a%$%k4XLg(B&ja.agent;$B$K$h$j$N$_;H$o$l$k$3$H$rA[Dj$7$F$$$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>

  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      The interpretation of the "unknown-8bit" is up to the mail reader.
   It is assumed that in many cases the human user will be able to
   interpret the information and choose an appropriate character set or
   pre-processor.
    </ja:l>
    <ja:l xml:lang="ja">
      "unknown-8bit" $B$N2r<a$O%a%$%k!&%j!<%@!<$K0Q$M$i$l$^$9!#B?$/$N>l9g$G$O?M4VMxMQ<T$,>pJs$r2r<a$7$FE,@Z$JJ8;z=89g$"$k$$$OA0=hM}4o$rA*Br$G$-$k$H;W$o$l$^$9!#(B
    </ja:l>
    </ja:pair>
  </t>

</section>

<section title="Acknowledgements" myns:unnumbered="yes">
  <t>
    <ja:pair>
    <ja:l xml:lang="en">
      This document originated as a hallway conversation between 
      Ned Freed, Neil Katin, and the author.  Substantive input 
      was received from Jonathan Laventhol, Craig Everhart, 
      Olle Jarnefors, and Olafur Gudmundsson.  The document was 
      refined with the input of many participants in the IETF SMTP 
      Extensions Working Group.
    </ja:l>
    <ja:l xml:lang="ja">
      $B$3$NJ8=q$O(B Ned Freed, Neil Katin $B$HCx<T$N0f8MC<2q5D$+$i@8$^$l$^$7$?!#(B
      Jonathan Laventhol, Craig Everhart, 
      Olle Jarnefors, Olafur Gudmundsson $B$,:2$r?a$-9~$s$G$/$l$^$7$?!#$3$NJ8=q$O(B
      IETF SMTP $B3HD%:n6HIt2q$N;22C<T$N0U8+$K$h$j@:O#$5$l$^$7$?!#(B
    </ja:l>
    </ja:pair>
  </t>
</section>

<ja:insert section="references" />


<section title="Security Considerations" myns:unnumbered="yes">
   <t>Security issues are not discussed in this memo.</t>
</section>

</middle>
<back>
  <references>
    <reference anchor="refs.RFC1341"><!-- [1] -->
      <front><title>Multipurpose Internet Mail Extensions</title>
             <ja:title xml:lang="ja">$BB?L\E*(B Internet $B%a%$%k3HD%(B</ja:title>
             <author initials="N." surname="Borenstein">
               <organization>Bellcore</organization>
             </author>
             <author initials="N." surname="Freed">
               <organization>Innosoft</organization>
             </author>
             <date month="June" year="1992" />
       </front>
      <seriesInfo name="RFC" value="1341" />
    </reference>
    <reference anchor="refs.RFC1342"><!-- [2] -->
      <front><title>Representation of Non-ASCII Text in Internet Message Headers</title>
             <ja:title xml:lang="ja">$BHs(B ASCII $BJ8$N(B Internet $B%a%C%;!<%8F,$K$*$1$kI=8=(B</ja:title>
             <author initials="K." surname="Moore">
               <organization>University of Tennessee</organization>
             </author>
             <date month="June" year="1992" />
      </front>
      <seriesInfo name="RFC" value="1342" />
    </reference>
    <reference anchor="refs.RFC1425"><!-- [3] -->
      <front><title>SMTP Service Extensions</title>
             <ja:title xml:lang="ja">SMTP $B%5!<%S%93HD%(B</ja:title>
             <author initials="J." surname="Klensin" ja:text="Klensin, J., WG Chair">
               <organization>United Nations University</organization>
             </author>
             <author initials="N." surname="Freed" ja:text="Freed, N., Editor">
               <organization>Innosoft International, Inc.</organization>
             </author>
             <author initials="M." surname="Rose">
               <organization>Dover Beach Consulting, Inc.</organization>
             </author>
             <author initials="E." surname="Stefferud">
               <organization>Network Management Associates, Inc.</organization>
             </author>
             <author initials="D." surname="Crocker">
               <organization>The Branch Office</organization>
             </author>
             <date month="February" year="1993" />
      </front>
      <seriesInfo name="RFC" value="1425" />
    </reference>
    <reference anchor="refs.RFC1426"><!-- [4] -->
      <front><title>SMTP Service Extensions for 8bit
       MIMEtransport</title>
             <ja:title xml:lang="ja">8$B%S%C%H(B MIME $BE>AwMQ(B SMTP $B%5!<%S%93HD%(B</ja:title>
             <author initials="J." surname="Klensin" ja:text="Klensin, J., WG Chair">
               <organization>United Nations University</organization>
             </author>
             <author initials="N." surname="Freed" ja:text="Freed, N., Editor">
               <organization>Innosoft International, Inc.</organization>
             </author>
             <author initials="M." surname="Rose">
               <organization>Dover Beach Consulting, Inc.</organization>
             </author>
             <author initials="E." surname="Stefferud">
               <organization>Network Management Associates, Inc.</organization>
             </author>
             <author initials="D." surname="Crocker">
               <organization>The Branch Office</organization>
             </author>
             <date month="February" year="1993" />
      </front>
      <seriesInfo name="RFC" value="1426" />
    </reference>
    <reference anchor="refs.ASCII"><!-- [5] -->
      <front><title>Coded Character Set$B!=!=(B7-Bit American Standard Code 
                    for Information Interchange</title>
             <ja:title xml:lang="ja">$BId9f2=J8;z=89g!=!=(B7$B%S%C%H$N>pJs8r49MQ0!JFMx2CI8=`Id9f(B</ja:title>
      </front>
      <seriesInfo name="ANSI" value="X3.4-1986" />
    </reference>
    <reference anchor="refs.STD2"><!-- [6] -->
      <front><title>Assigned Numbers</title>
             <ja:title xml:lang="ja">$B3dEvHV9f(B</ja:title>
             <author initials="J." surname="Reynolds">
               <organization>USC/Information Sciences Institute</organization>
             </author>
             <author initials="J." surname="Postel">
               <organization>USC/Information Sciences Institute</organization>
             </author>
             <date month="July" year="1992" />
       </front>
      <seriesInfo name="STD" value="2" />
      <seriesInfo name="RFC" value="1340" />
    </reference>
  </references>
</back>
</rfc>