rfc1651.txt

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   Other improperly-implemented servers will not accept a HELO command
   after EHLO has been sent and rejected.  In some cases, this problem
   can be worked around by sending a RSET after the failure response to
   EHLO, then sending the HELO.  Clients that do this should be aware
   that many implementations will return a failure code (e.g., 503 Bad
   sequence of commands) in response to the RSET.  This code can be
   safely ignored.

5.  Initial IANA Registry

   The IANA's initial registry of SMTP service extensions consists of
   these entries:

   Service Ext   EHLO Keyword Parameters Verb       Added Behavior
   ------------- ------------ ---------- ---------- ------------------
   Send             SEND         none       SEND    defined in RFC 821
   Send or Mail     SOML         none       SOML    defined in RFC 821
   Send and Mail    SAML         none       SAML    defined in RFC 821
   Expand           EXPN         none       EXPN    defined in RFC 821
   Help             HELP         none       HELP    defined in RFC 821
   Turn             TURN         none       TURN    defined in RFC 821





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   which correspond to those SMTP commands which are defined as optional
   in [5].  (The mandatory SMTP commands, according to [5], are HELO,
   MAIL, RCPT, DATA, RSET, VRFY, NOOP, and QUIT.)

6.  MAIL FROM and RCPT TO Parameters

   It is recognized that several of the extensions planned for SMTP will
   make use of additional parameters associated with the MAIL FROM and
   RCPT TO command. The syntax for these commands, again using the ABNF
   notation of [2] as well as underlying definitions from [1], is:

  esmtp-cmd        ::= inner-esmtp-cmd [SP esmtp-parameters] CR LF
  esmtp-parameters ::= esmtp-parameter *(SP esmtp-parameter)
  esmtp-parameter  ::= esmtp-keyword ["=" esmtp-value]
  esmtp-keyword    ::= (ALPHA / DIGIT) *(ALPHA / DIGIT / "-")

                       ; syntax and values depend on esmtp-keyword
  esmtp-value      ::= 1*<any CHAR excluding "=", SP, and all
                          control characters (US-ASCII 0-31
                          inclusive)>

                       ; The following commands are extended to
                       ; accept extended parameters.
  inner-esmtp-cmd  ::= ("MAIL FROM:<" reverse-path ">")   /
                       ("RCPT TO:<" forward-path ">")

   All esmtp-keyword values must be registered as part of the IANA
   registration process described above. This definition only provides
   the framework for future extension; no extended MAIL FROM or RCPT TO
   parameters are defined by this RFC.

6.1.  Error responses

   If the server SMTP does not recognize or cannot implement one or more
   of the parameters associated with a particular MAIL FROM or RCPT TO
   command, it will return code 555.

   If for some reason the server is temporarily unable to accomodate one
   or more of the parameters associated with a MAIL FROM or RCPT TO
   command, and if the definition of the specific parameter does not
   mandate the use of another code, it should return code 455.

   Errors specific to particular parameters and their values will be
   specified in the parameter's defining RFC.







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RFC 1651                SMTP Service Extensions                July 1994


7.  Received: Header Field Annotation

   SMTP servers are required to add an appropriate Received: field to
   the headers of all messages they receive. A "with ESMTP" clause
   should be added to this field when any SMTP service extensions are
   used. "ESMTP" is hereby added to the list of standard protocol names
   registered with IANA.

8.  Usage Examples

   (1)  An interaction of the form:

        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
         ...

        indicates that the server SMTP implements only those SMTP
        commands which are defined as mandatory in [5].


   (2)  In contrast, an interaction of the form:

        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-EXPN
        S: 250-HELP
        S: 250-8BITMIME
        S: 250-XONE
        S: 250 XVRB
         ...

        indicates that the server SMTP also implements the SMTP
        EXPN and HELP commands, one standard service extension
        (8BITMIME), and two non-standard service extensions (XONE
        and XVRB).


   (3)  Finally, a server that does not support SMTP service
        extensions would act as follows:

        S: <wait for connection on TCP port 25>
        C: <open connection to server>



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        S: 220 dbc.mtview.ca.us SMTP service ready
        C: EHLO ymir.claremont.edu
        S: 500 Command not recognized: EHLO
         ...

        The 500 response indicates that the server SMTP does not
        implement the extensions specified here.  The client
        would normally send a HELO command and proceed as
        specified in RFC 821.   See section 4.7 for additional
        discussion.

9.  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 RFC-821.  It does
   provide an announcement of server mail capabilities via the response
   to the EHLO verb. However, all information provided by announcement
   of any of the initial set of service extensions defined by this RFC
   can be readily deduced by selective probing of the verbs required to
   transport and deliver mail. The security implications of service
   extensions described in other RFCs should be dealt with in those
   RFCs.

10.  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, Dan Oscarsson, Julian Onions, 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.

11.  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.



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RFC 1651                SMTP Service Extensions                July 1994


   [3] Borenstein, N., and N. Freed, "Multipurpose Internet Mail
       Extensions", RFC 1521, Bellcore, Innosoft, September 1993.

   [4] Moore, K., "Representation of Non-ASCII Text in Internet Message
       Headers", RFC 1522, University of Tennessee, September 1993.

   [5] Braden, R., "Requirements for Internet Hosts - Application and
       Support", STD 3, RFC 1123, USC/Information Sciences Institute,
       October 1989.

12.  Chair, Editor, and Authors' Addresses

   John Klensin, WG Chair
   MCI Data Services Division
   2100 Reston Parkway, 6th floor
   Reston, VA 22091
   USA

   Phone:: [phone]
   Fax: [phone]
   EMail: [e-mail]


   Ned Freed, Editor
   Innosoft International, Inc.
   1050 East Garvey Avenue South
   West Covina, CA 91790
   USA

   Phone:: [phone]
   Fax: [phone]
   EMail: [e-mail]


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

   Phone: [phone]
   Fax: [phone]
   EMail: [e-mail]








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RFC 1651                SMTP Service Extensions                July 1994


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

   Phone: [phone]
   Fax: [phone]
   EMail: [e-mail]


   Dave Crocker
   Silicon Graphics, Inc.
   2011 N. Shoreline Blvd.
   P.O. Box 7311
   Mountain View, CA 94039
   USA

   Phone: [phone]
   Fax: [phone]
   EMail: [e-mail]






























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