Network Working Group                               J. Klensin, WG Chair
Request for Comments: 1426                     United Nations University
                                                       N. Freed, Editor
                                           Innosoft International, Inc.
                                                                M. Rose
                                           Dover Beach Consulting, Inc.
                                                           E. Stefferud
                                    Network Management Associates, Inc.
                                                             D. Crocker
                                                      The Branch Office
                                                          February 1993


                        SMTP Service Extension
                        for 8bit-MIMEtransport

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.

1.  Abstract

  This memo defines an extension to the SMTP service whereby an SMTP
  content body containing octets outside of the US ASCII octet range
  (hex 00-7F) may be relayed using SMTP.

2.  Introduction

  Although SMTP is widely and robustly deployed, various extensions
  have been requested by parts of the Internet community. In
  particular, a significant portion of the Internet community wishes to
  exchange messages in which the content body consists of a MIME
  message [3] containing arbitrary octet-aligned material. This memo
  uses the mechanism described in [5] to define an extension to the
  SMTP service whereby such contents may be exchanged. Note that this
  extension does NOT eliminate the possibility of an SMTP server
  limiting line length; servers are free to implement this extension
  but nevertheless set a line length limit no lower than 1000 octets.

3.  Framework for the 8bit MIME Transport Extension

  The 8bit MIME transport extension is laid out as follows:





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         (1)  the name of the SMTP service extension defined here is
              8bit-MIMEtransport;

         (2)  the EHLO keyword value associated with the extension is
              8BITMIME;

         (3)  no parameter is used with the 8BITMIME EHLO keyword;

         (4)  one optional parameter using the keyword BODY is added to
              the MAIL FROM command.  The value associated with this
              parameter is a keyword indicating whether a 7bit message
              (in strict compliance with [1]) or a MIME message (in
              strict compliance with [3]) with arbitrary octet content
              is being sent. The syntax of the value is as follows,
              using the ABNF notation of [2]:

                   body-value ::= "7BIT" / "8BITMIME"

         (5)  no additional SMTP verbs are defined by this extension;
              and,

         (6)  the next section specifies how support for the extension
              affects the behavior of a server and client SMTP.

4.  The 8bit-MIMEtransport service extension

  When a client SMTP wishes to submit (using the MAIL command) a
  content body consisting of a MIME message containing arbitrary
  octet-aligned material, it first issues the EHLO command to the
  server SMTP. If the server SMTP responds with code 250 to the EHLO
  command, and the response includes the EHLO keyword value 8BITMIME,
  then the server SMTP is indicating that it supports the extended MAIL
  command and will accept MIME messages containing arbitrary octet-
  aligned material.

  The extended MAIL command is issued by a client SMTP when it wishes
  to transmit a content body consisting of a MIME message containing
  arbitrary octet-aligned material. The syntax for this command is
  identical to the MAIL command in [1], except that a BODY parameter
  must appear after the address.

  The complete syntax of this extended command is defined in [5]. The
  esmtp-keyword is BODY and the syntax for esmtp-value is given by the
  syntax for body-value shown above.

  The value associated with the BODY parameter indicates whether the
  content body which will be passed using the DATA command consists of
  a MIME message containing some arbitrary octet-aligned material



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RFC 1426                SMTP 8bit-MIMEtransport            February 1993


  ("8BITMIME") or is encoded entirely in accordance with [1] ("7BIT").

  A server which supports the 8-bit MIME transport service extension
  shall preserve all bits in each octet passed using the DATA command.

  Naturally, the usual SMTP data-stuffing algorithm applies so that a
  content which contains the five-character sequence of

              <CR> <LF> <DOT> <CR> <LF>

  or a content that begins with the three-character sequence of

              <DOT> <CR> <LF>

  does not prematurely terminate the transfer of the content.  Further,
  it should be noted that the CR-LF pair immediately preceeding the
  final dot is considered part of the content.  Finally, although the
  content body contains arbitrary octet-aligned material, the length of
  each line (number of octets between two CR-LF pairs), is still
  subject to SMTP server line length restrictions (which may allow as
  few as 1000 octets on a single line).

  Once a server SMTP supporting the 8bit-MIMEtransport service
  extension accepts a content body containing octets with the high-
  order (8th) bit set, the server SMTP must deliver or relay the
  content in such a way as to preserve all bits in each octet.

  If a server SMTP does not support the 8-bit MIME transport extension
  (either by not responding with code 250 to the EHLO command, or by
  not including the EHLO keyword value 8BITMIME in its response), then
  the client SMTP must not, under any circumstances, attempt to
  transfer a content which contains characters outside the US ASCII
  octet range (hex 00-7F).

  A client SMTP has two options in this case: first,  it may implement
  a gateway transformation to convert the message into valid 7bit MIME,
  or second, or may treat this as a permanent error and handle it in
  the usual manner for delivery failures.  The specifics of the
  transformation from 8bit MIME to 7bit MIME are not described by this
  RFC; the conversion is nevertheless constrained in the following
  ways:

         (1)  it must cause no loss of information; MIME transport
              encodings must be employed as needed to insure this is
              the case, and

         (2)  the resulting message must be valid 7bit MIME.




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RFC 1426                SMTP 8bit-MIMEtransport            February 1993


5.  Usage Example

  The following dialogue illustrates the use of the 8bit-MIMEtransport
  service extension:

         S: <wait for connection on TCP port 25>
         C: <open connection to server>
         S: 220 dbc.mtview.ca.us SMTP service ready
         C: EHLO ymir.claremont.edu
         S: 250-dbc.mtview.ca.us says hello
         S: 250 8BITMIME
         C: MAIL FROM:<[email protected]> BODY=8BITMIME
         S: 250 <[email protected]>... Sender and 8BITMIME ok
         C: RCPT TO:<[email protected]>
         S: 250 <[email protected]>... Recipient ok
         C: DATA
         S: 354 Send 8BITMIME message, ending in CRLF.CRLF.
          ...
         C: .
         S: 250 OK
         C: QUIT
         S: 250 Goodbye

6.  Security Considerations

  This RFC does not discuss security issues and is not believed to
  raise any security issues not already endemic in electronic mail and
  present in fully conforming implementations of [1].

7.  Acknowledgements

  This document represents a synthesis of the ideas of many people and
  reactions to the ideas and proposals of others.  Randall Atkinson,
  Craig Everhart, Risto Kankkunen, and Greg Vaudreuil contributed ideas
  and text sufficient to be considered co-authors.  Other important
  suggestions, text, or encouragement came from Harald Alvestrand, Jim
  Conklin, Mark Crispin, Frank da Cruz, 'Olafur Gudmundsson, Per
  Hedeland, Christian Huitma, Neil Katin, Eliot Lear, Harold A.
  Miller, Keith Moore, Dan Oscarsson, Julian Onions, Neil Rickert, John
  Wagner, Rayan Zachariassen, and the contributions of the entire IETF
  SMTP Working Group. Of course, none of the individuals are
  necessarily responsible for the combination of ideas represented
  here. Indeed, in some cases, the response to a particular criticism
  was to accept the problem identification but to include an entirely
  different solution from the one originally proposed.






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RFC 1426                SMTP 8bit-MIMEtransport            February 1993


8.  References

  [1] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
      USC/Information Sciences Institute, August 1982.

  [2] Crocker, D., "Standard for the Format of ARPA Internet Text
      Messages", STD 11, RFC 822, UDEL, August 1982.

  [3] Borenstein, N., and N. Freed, "Multipurpose Internet Mail
      Extensions", RFC 1341, Bellcore, Innosoft, June 1992.

  [4] Moore, K., "Representation of Non-ASCII Text in Internet Message
      Headers", RFC 1342, University of Tennessee, June 1992.

  [5] Klensin, J., WG Chair, Freed, N., Editor, Rose, M., Stefferud,
      E., and D. Crocker, "SMTP Service Extensions" RFC 1425, United
      Nations University, Innosoft International, Inc., Dover Beach
      Consulting, Inc., Network Management Associates, Inc., The Branch
      Office, February 1993.

  [6] Partridge, C., "Mail Routing and the Domain System", RFC 974,
      BBN, January 1986.

9.  Chair, Editor, and Authors' Addresses

      John Klensin, WG Chair
      United Nations University
      PO Box 500, Charles Street Station
      Boston, MA 02114-0500  USA

      Phone: +1 617 227 8747
      Fax: +1 617 491 6266
      Email: [email protected]


      Ned Freed, Editor
      Innosoft International, Inc.
      250 West First Street, Suite 240
      Claremont, CA 91711  USA

      Phone: +1 909 624 7907
      Fax: +1 909 621 5319
      Email: [email protected]








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RFC 1426                SMTP 8bit-MIMEtransport            February 1993


      Marshall T. Rose
      Dover Beach Consulting, Inc.
      420 Whisman Court
      Moutain View, CA  94043-2186  USA

      Phone: +1 415 968 1052
      Fax: +1 415 968 2510
      Email: [email protected]


      Einar A. Stefferud
      Network Management Associates, Inc.
      17301 Drey Lane
      Huntington Beach, CA, 92647-5615  USA

      Phone: +1 714 842 3711
      Fax: +1 714 848 2091
      Email: [email protected]


      David H. Crocker
      The Branch Office
      USA

      Email: [email protected]


























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