SmtpClient不会通过SSL/TLS进行身份验证(不指向gmail)

我有一个ssl/tls服务器(nodejs)，它作为后缀/sendmail的代理，对发送的邮件执行一些预处理/数据采集。

var sslStream = new SslStream(tcpClient.GetStream(), false,
                         new RemoteCertificateValidationCallback(CertificateValidation),
                         new LocalCertificateSelectionCallback(CertificateSelectionCallback));
                string fn = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "cert.pem");
                X509Certificate c = X509Certificate.CreateFromCertFile(fn);
                var certs = new X509CertificateCollection();
                certs.Add(c);
                sslStream.AuthenticateAsClient(System.Environment.MachineName, certs , SslProtocols.Default, false);

然而，我不能得到SmtpClient连接。顶层错误是超时，但是我已经调试到SmtpClient/SmtpConnection，底层错误是流不可读，大概是因为它从未经过身份验证(我不能在我的ssl/tls代理服务器中使用SmtpClient代码命中断点，但是上面的手动sslConnection工作得很好)。

如果有一种方法可以手动提供底层通信流到SmtpClient，但我找不到一种方法来做到这一点，那将是伟大的。

有人知道为什么下面的代码不能验证吗?

这是我一直在使用的测试应用程序，试图连接SmtpClient没有成功:

    ServicePointManager.ServerCertificateValidationCallback = CertificateValidation;
    // Using Ssl3 rather than Tls here makes no difference
    ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;
    var client = new SmtpClient {
                                  Timeout = 10000,
                                  DeliveryMethod = SmtpDeliveryMethod.Network,
                                  EnableSsl = true,
                                  UseDefaultCredentials = false,
                                  Host = "192.168.15.71",
                                  Port = 10126
                                };
    client.ClientCertificates.Add(c);
    client.Credentials = new NetworkCredential("username", "password");
    //times out here, except the real exception that doesn't bubble up is the stream
    //isnt readable because it never authenticated (when it trys to read the status
    //returned by the smtp server, eg: "220 smtp2.example.com ESMTP Postfix")
    client.send(email);