code: public void start() throws IOException {
  		// try to automatically retrieve a port
  		port = SocketUtils.getNextFreePort(PORT_RANGE_START, PORT_RANGE_END);
  
  		server = SafeCloseSmtpServer.start(port);
  	}
docs: Start the server, port is chosen automatically in the range of {@value #PORT_RANGE_START} and
  {@value #PORT_RANGE_END}.
  
  @throws IOException if no port is available