SMTP Service Extension for 8bit-MIMEtransport (RFC1426)
Original Publication Date: 1993-Feb-01
Included in the Prior Art Database: 2019-Feb-10
Internet Society Requests For Comment (RFCs)
J. Klensin: AUTHOR [+5]
This memo defines an extension to the SMTP service whereby an SMTP content body containing octets outside of the US ASCII octet range (hex
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.
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.
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  containing arbitrary octet-aligned material. This memo uses the mechanism described in  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 ) or a MIME message (in strict compliance with ) with arbitrary octet content is being sent. The syntax of the value is as follows, using the ABNF notation of :
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 arbitr...