rfc1869.txt

用C#开发实现SMTP相关技术,能接收到带附件的邮件服务功能.

   In the case of any error response, the client SMTP should issue
   either the HELO or QUIT command.

4.6.  Responses from servers without extensions

   A server SMTP that conforms to RFC 821 but does not support the
   extensions specified here will not recognize the EHLO command and
   will consequently return code 500, as specified in RFC 821.  The
   server SMTP should stay in the same state after returning this code
   (see section 4.1.1 of RFC 821).  The client SMTP may then issue
   either a HELO or a QUIT command.

4.7.  Responses from improperly implemented servers

   Some SMTP servers are known to disconnect the SMTP transmission
   channel upon receipt of the EHLO command. The disconnect can occur
   immediately or after sending a response.  Such behavior violates
   section 4.1.1 of RFC 821, which explicitly states that disconnection
   should only occur after a QUIT command is issued.

   Nevertheless, in order to achieve maxmimum interoperablity it is
   suggested that extended SMTP clients using EHLO be coded to check for
   server connection closure after EHLO is sent, either before or after



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RFC 1869                SMTP Service Extensions            November 1995


   returning a reply.  If this happens the client must decide if the
   operation can be successfully completed without using any SMTP
   extensions. If it can a new connection can be opened and the HELO
   command can be used.

   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

   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)>




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RFC 1869                SMTP Service Extensions            November 1995


                          ; 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.

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].






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RFC 1869                SMTP Service Extensions            November 1995


 (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 nonstandard and unregistered
       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>
       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.




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RFC 1869                SMTP Service Extensions            November 1995


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, Keith Moore, John Myers, 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.

   [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 Author Addresses

   John Klensin, WG Chair
   MCI
   2100 Reston Parkway
   Reston, VA 22091

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






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RFC 1869                SMTP Service Extensions            November 1995


   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]


   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
   Brandenburg Consulting
   675 Spruce Dr.
   Sunnyvale, CA 94086 USA
   USA

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









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