SMTP Service Extension for 8-bit MIME Transport
RFC 6152

Document Type RFC - Internet Standard (March 2011; Errata)
Obsoletes RFC 1652
Also known as STD 71
Authors Dave Crocker  , John Klensin  , Marshall Rose  , Ned Freed 
Last updated 2019-03-06
Stream IETF
Formats plain text html pdf htmlized bibtex
Stream WG state (None)
Document shepherd No shepherd assigned
IESG IESG state RFC 6152 (Internet Standard)
Action Holders
Consensus Boilerplate Unknown
Telechat date
Responsible AD Alexey Melnikov
Send notices to (None)
Internet Engineering Task Force (IETF)                        J. Klensin
Request for Comments: 6152
STD: 71                                                         N. Freed
Obsoletes: 1652                                                   Oracle
Category: Standards Track                                        M. Rose
ISSN: 2070-1721                             Dover Beach Consulting, Inc.
                                                         D. Crocker, Ed.
                                             Brandenburg InternetWorking
                                                              March 2011

            SMTP Service Extension for 8-bit MIME Transport


   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.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Klensin, et al.              Standards Track                    [Page 1]
RFC 6152              SMTP Extension for 8-bit MIME           March 2011

1.  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 [RFC2045][RFC2046][RFC5322] containing arbitrary octet-
   aligned material.  This memo uses the mechanism described in the SMTP
   specification [RFC5321] 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.

2.  Framework for the 8-bit MIME Transport Extension

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

   1.  the name of the SMTP service extension defined here is

   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 command.  The value associated with this parameter is a
       keyword indicating whether a 7-bit message (in strict compliance
       with [RFC5321]) or a MIME message (in strict compliance with
       [RFC2046] and [RFC2045]) with arbitrary octet content is being
       sent.  The syntax of the value is as follows, using the ABNF
       notation of [RFC5234]:

       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.

3.  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

Klensin, et al.              Standards Track                    [Page 2]
RFC 6152              SMTP Extension for 8-bit MIME           March 2011

   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
Show full document text