code: public static SMTPClientTransportFactory createNio(int workerCount) {
          return new NettySMTPClientTransportFactory(new NioClientSocketChannelFactory(Executors.newCachedThreadPool(), Executors.newCachedThreadPool(), workerCount), FACTORY);
      }
docs: Create a new NIO based {@link SMTPClientTransportFactory}
  
  @param workerCount
  @return factory