A full session example

      S: <wait for connection on TCP port 110>
      C: <open connection>
      S:    +OK POP3 server ready <1896.697170952@dbc.mtview.ca.us>
      C:    APOP mrose c4c9334bac560ecc979e58001b3e22fb
      S:    +OK mrose's maildrop has 2 messages (320 octets)
      C:    STAT
      S:    +OK 2 320
      C:    LIST
      S:    +OK 2 messages (320 octets)
      S:    1 120
      S:    2 200
      S:    .
      C:    RETR 1
      S:    +OK 120 octets
      S:    <the POP3 server sends message 1>
      S:    .
      C:    DELE 1
      S:    +OK message 1 deleted
      C:    RETR 2
      S:    +OK 200 octets
      S:    <the POP3 server sends message 2>
      S:    .
      C:    DELE 2
      S:    +OK message 2 deleted
      C:    QUIT
      S:    +OK dewey POP3 server signing off (maildrop empty)
      C:  <close connection>
      S:  <wait for next connection>