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authorThomas Voss <mail@thomasvoss.com> 2024-11-27 20:54:24 +0100
committerThomas Voss <mail@thomasvoss.com> 2024-11-27 20:54:24 +0100
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+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:
+
+
+
+
+
+Klensin, Freed, Rose, Stefferud & Crocker [Page 1]
+
+RFC 1426 SMTP 8bit-MIMEtransport February 1993
+
+
+ (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
+
+
+
+Klensin, Freed, Rose, Stefferud & Crocker [Page 2]
+
+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.
+
+
+
+
+Klensin, Freed, Rose, Stefferud & Crocker [Page 3]
+
+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:<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
+ 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.
+
+
+
+
+
+
+Klensin, Freed, Rose, Stefferud & Crocker [Page 4]
+
+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: klensin@infoods.unu.edu
+
+
+ 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: ned@innosoft.com
+
+
+
+
+
+
+
+
+Klensin, Freed, Rose, Stefferud & Crocker [Page 5]
+
+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: mrose@dbc.mtview.ca.us
+
+
+ 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: stef@nma.com
+
+
+ David H. Crocker
+ The Branch Office
+ USA
+
+ Email: dcrocker@mordor.stanford.edu
+
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+Klensin, Freed, Rose, Stefferud & Crocker [Page 6]
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