private SimpleSmtpServer(Configuration configuration)
 {
     this.Configuration = configuration;
     this.ServerReady = new AutoResetEvent(false);
 }
 internal static SimpleSmtpServer Start(Configuration configuration)
 {
     var server = new SimpleSmtpServer(configuration);
     new Thread(new ThreadStart(server.StartListening)).Start();
     server.ServerReady.WaitOne();
     return server;
 }