POP3 Command Summary

Minimal POP3 Commands:

      USER name               valid in the AUTHORIZATION state
      PASS string
      QUIT

      STAT                    valid in the TRANSACTION state
      LIST [msg]
      RETR msg
      DELE msg
      NOOP
      RSET

      QUIT                    valid in the UPDATE state

   Optional POP3 Commands:

      APOP name digest        valid in the AUTHORIZATION state

      TOP msg n               valid in the TRANSACTION state
      UIDL [msg]

   POP3 Replies:

      +OK
      -ERR