do_start

# File lib/net/smtp.rb, line 542
    def do_start(helo_domain, user, secret, authtype)
      raise IOError, 'SMTP session already started' if @started
      if user or secret
        check_auth_method(authtype || DEFAULT_AUTH_TYPE)
        check_auth_args user, secret
      end
      s = Timeout.timeout(@open_timeout, Net::OpenTimeout) do
        tcp_socket(@address, @port)
      end
      logging "Connection opened: #{@address}:#{@port}"
      @socket = new_internet_message_io(tls? ? tlsconnect(s) : s)
      check_response critical { recv_response() }
      do_helo helo_domain
      if starttls_always? or (capable_starttls? and starttls_auto?)
        unless capable_starttls?
          raise SMTPUnsupportedCommand,
              "STARTTLS is not supported on this server"
        end
        starttls
        @socket = new_internet_message_io(tlsconnect(s))
        # helo response may be different after STARTTLS
        do_helo helo_domain
      end
      authenticate user, secret, (authtype || DEFAULT_AUTH_TYPE) if user
      @started = true
    ensure
      unless @started
        # authentication failed, cancel connection.
        s.close if s
        @socket = nil
      end
    end