class Net::SMTP

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 = tcp_socket(@address, @port)
  logging "Connection opened: #{@address}:#{@port}"
  @socket = new_internet_message_io(tls? ? tlsconnect(s, @ssl_context_tls) : s)
  check_response critical { recv_response() }
  do_helo helo_domain
  if ! tls? and (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, @ssl_context_starttls))
    # 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