
Network Working Group                   John Klensin, WG Chair
Internet Draft                               Ned Freed, Editor
<draft-ietf-smtpext-8bitmime-03.txt>             Marshall Rose
                                               Einar Stefferud
                                                 David Crocker

                    SMTP Service Extension
                    for 8bit-MIMEtransport

                         May 6, 1995



                     Status of this Memo

This document is an Internet-Draft.  Internet-Drafts are
working documents of the Internet Engineering Task Force
(IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-
Drafts.

Internet-Drafts are draft documents valid for a maximum of six
months. Internet-Drafts may be updated, replaced, or obsoleted
by other documents at any time.  It is not appropriate to use
Internet-Drafts as reference material or to cite them other
than as a "working draft" or "work in progress".

To learn the current status of any Internet-Draft, please
check the 1id-abstracts.txt listing contained in the
Internet-Drafts Shadow Directories on ds.internic.net (US East
Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast),
or munnari.oz.au (Pacific Rim).

This draft is intended to supercede RFC 1652. The only
significant change has been to bring the definition of
8bitMIME into alignment with the definition in the MIME
specification.


1.  Abstract

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











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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. Given that this restriction still applies,
this extension does NOT provide a means for transferring
unencoded binary via SMTP.


3.  Framework for the 8bit MIME Transport Extension

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

 (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)   The maximum length of a MAIL FROM command line is
       increased by 14 characters by the possible addition of
       the BODY keyword and value;







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

 (7)   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
lines of 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 that use the capabilities of the 8bit
MIME content-transfer-encoding.

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 lines of 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.  Only one BODY parameter may be used in a single MAIL
command.

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 8-bit material
("8BITMIME") in accordance with [3] 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






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     <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 lines of
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). This restriction means that
this extension MAY provide the necessary facilities for
transferring a MIME object with the 8BIT content-transfer-
encoding, it DOES NOT provide a means of transferring an
object with the BINARY content-transfer-encoding.

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 with values greater than hex 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







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


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:<ned@ymir.claremont.edu> BODY=8BITMIME
S: 250 <ned@ymir.claremont.edu>... Sender and 8BITMIME ok
C: RCPT TO:<mrose@dbc.mtview.ca.us>
S: 250 <mrose@dbc.mtview.ca.us>... 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





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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.


8.  References

[1]  J.B. Postel.  Simple Mail Transfer Protocol.  Request for
     Comments 821, (August, 1982).

[2]  D.H. Crocker.  Standard for the Format of ARPA Internet
     Text Messages.  Request for Comments 822, (August, 1982).

[3]  N.S. Borenstein, N. Freed.  Multipurpose Internet Mail
     Extensions.  Request for Comments 1521, (September,
     1993).

[4]  K. Moore.  Representation of Non-ASCII Text in Internet
     Message Headers.  Request for Comments 1522, (September,
     1993).

[5]  M.T. Rose, E.A. Stefferud, D.H. Crocker, J.C. Klensin,
     N. Freed.  SMTP Service Extensions.  Internet-Draft,
     (April, 1995).

[6]  C. Partridge.  Mail Routing and the Domain System.
     Request for Comments 974, (January, 1986).



















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9.  Chair, Editor, and Author Addresses

John Klensin, WG Chair
MCI
2100 Reston Parkway
Reston, VA 22091
 tel: +1 703 715-7361           fax: +1 703 715-7436
 email: klensin@mci.net

Ned Freed, Editor
Innosoft International, Inc.
1050 East Garvey Avenue South
West Covina, CA 91790
USA
 tel: +1 818 919 3600           fax: +1 818 919 3614
 email: ned@innosoft.com

Marshall T. Rose
Dover Beach Consulting, Inc.
420 Whisman Court
Moutain View, CA  94043-2186
USA
 tel: +1 415 968 1052           fax: +1 415 968 2510
 email: mrose@dbc.mtview.ca.us

Einar A. Stefferud
Network Management Associates, Inc.
17301 Drey Lane
Huntington Beach, CA, 92647-5615
USA
 tel: +1 714 842 3711           fax: +1 714 848 2091
 email: stef@nma.com

Dave Crocker
Brandenburg Consulting
675 Spruce Dr.
Sunnyvale, CA 94086 USA
USA
 tel: +1 408 246 8253           fax: +1 408 249 6205
 email: dcrocker@mordor.stanford.edu










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