First the user's name is verified, then an attempt is made to send to the user's terminal. When that fails, the messages is mailed to the user's mailbox.
R: 220 SU-SCORE.ARPA Simple Mail Transfer Service Ready S: HELO MIT-MC.ARPA R: 250 SU-SCORE.ARPA S: VRFY Crispin R: 250 Mark Crispin <Admin.MRC@SU-SCORE.ARPA> S: SEND FROM:<EAK@MIT-MC.ARPA> R: 250 OK S: RCPT TO:<Admin.MRC@SU-SCORE.ARPA> R: 450 User not active now S: RSET R: 250 OK S: MAIL FROM:<EAK@MIT-MC.ARPA> R: 250 OK S: RCPT TO:<Admin.MRC@SU-SCORE.ARPA> R: 250 OK S: DATA R: 354 Start mail input; end with <CRLF>.<CRLF> S: Blah blah blah... S: ...etc. etc. etc. S: . R: 250 OK S: QUIT R: 221 SU-SCORE.ARPA Service closing transmission channel Scenario 5
Doing the preceding scenario more efficiently.
R: 220 SU-SCORE.ARPA Simple Mail Transfer Service Ready S: HELO MIT-MC.ARPA R: 250 SU-SCORE.ARPA S: VRFY Crispin R: 250 Mark Crispin <Admin.MRC@SU-SCORE.ARPA> S: SOML FROM:<EAK@MIT-MC.ARPA> R: 250 OK S: RCPT TO:<Admin.MRC@SU-SCORE.ARPA> R: 250 User not active now, so will do mail. S: DATA R: 354 Start mail input; end with <CRLF>.<CRLF> S: Blah blah blah... S: ...etc. etc. etc. S: . R: 250 OK S: QUIT R: 221 SU-SCORE.ARPA Service closing transmission channel Scenario 6