SmtpClient SSL 发送邮件异常排查

上周使用 SmtpCliet 发送邮件测试，在服务端配置 SSL 465 / 993 情况 ,客户端使用 465 SSL 端口发送邮件异常，测试代码如下:

 System.Net.ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(RemoteServerCertificateValidationCallback);

                SmtpClient smtp = new SmtpClient();
                smtp.EnableSsl = true;
                smtp.Port = ;
                smtp.UseDefaultCredentials = false;
                smtp.DeliveryMethod = SmtpDeliveryMethod.Network;//指定电子邮件发送方式
                smtp.Host =txtSMTP.Text ;//指定SMTP服务器
.....

=>如上代码在 调用 smtp.send() 方法后 ，客户端假死，邮件服务器日志显示:

Performing SSL/TLS handshake for session 829. Verify certificate: False

=>将 smtp.EnableSsl 设为  false ，使用25端口，发送正常。 因此推断，加密通道验证有问题。 将邮件服务端 smtp:25 端口安全验证规则改为:  STARTTLS(Required) , smtp:465端口仍保持: SSL/TLS ， 客户端代码如下 , 邮件发送成功。

System.Net.ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(RemoteServerCertificateValidationCallback);

                SmtpClient smtp = new SmtpClient();
                smtp.EnableSsl = true;
                smtp.UseDefaultCredentials = false;
                smtp.DeliveryMethod = SmtpDeliveryMethod.Network;//指定电子邮件发送方式
                smtp.Host =txtSMTP.Text ;//指定SMTP服务器
.....

 private bool RemoteServerCertificateValidationCallback(object sender, System.Security.Cryptography.X509Certificates.X509Certificate certificate, System.Security.Cryptography.X509Certificates.X509Chain chain, System.Net.Security.SslPolicyErrors sslPolicyErrors)
        {
            Console.WriteLine(certificate);

            return true;
        }

备注:

查阅MSDN ， SmtpClient 版本只支持 Explicit SSL    客户端链路过程如: Connect on 25 -> StartTLS (starts to encrypt) -> authenticate -> send data

http://cn.bing.com/search?q=c%23+mail+ssl&FORM=QSRE1

https://stackoverflow.com/questions/1011245/how-can-i-send-emails-through-ssl-smtp-with-the-net-framework

https://blogs.msdn.microsoft.com/webdav_101/2008/06/02/system-net-mail-with-ssl-to-authenticate-against-port-465/

https://msdn.microsoft.com/zh-cn/library/system.net.mail.smtpclient.enablessl(v=vs.110).aspx

--隐示SSL 示例:

http://blog.csdn.net/qxyywy/article/details/73962948