RFC788







                     SIMPLE MAIL TRANSFER PROTOCOL



                           Jonathan B. Postel






























                             November 1981



                     Information Sciences Institute
                   University of Southern California
                           4676 Admiralty Way
                   Marina del Rey, California  90291

                             (213) 822-1511

RFC 788                                                    November 1981
                                           Simple Mail Transfer Protocol



                           TABLE OF CONTENTS

   1.  INTRODUCTION .................................................. 1

   2.  THE SMTP MODEL ................................................ 2

   3.  THE SMTP PROCEDURE ............................................ 4

      3.1.  Mail ..................................................... 4
      3.2.  Forwarding ............................................... 7
      3.3.  Verifying and Expanding .................................. 8
      3.4.  Sending and Mailing ..................................... 10
      3.5.  Opening and Closing ..................................... 12
      3.6.  Relaying ................................................ 13
      3.7.  Domains ................................................. 15

   4.  THE SMTP SPECIFICATIONS ...................................... 16

      4.1.  SMTP Commands ........................................... 16
      4.1.1.  Command Semantics ..................................... 16
      4.1.2.  Command Syntax ........................................ 23
      4.2.  SMTP Replies ............................................ 28
      4.2.1.  Reply Codes by Function Group ......................... 29
      4.2.2.  Reply Codes in Numeric Order .......................... 30
      4.3.  Sequencing of Commands and Replies ...................... 31
      4.4.  State Diagrams .......................................... 33
      4.5.  Details ................................................. 35
      4.5.1.  Minimum Implementation ................................ 35
      4.5.2.  Transparency .......................................... 35
      4.5.3.  Sizes ................................................. 36

   APPENDIX A:  TCP ................................................. 38
   APPENDIX B:  NCP ................................................. 39
   APPENDIX C:  NITS ................................................ 40
   APPENDIX D:  X.25 ................................................ 41
   APPENDIX E:  Theory of Reply Codes ............................... 42
   APPENDIX F:  Scenarios ...........................................