465端口发送邮件失败

您好，我现在用C#编程发送邮件，用smtp.xxx.com.cn 25端口发送，可以发送成功。用465端口发送失败。主要代码如下：

方法一：

System.Net.Mail.MailMessage mailMessage = new System.Net.Mail.MailMessage();
mailMessage.From = new MailAddress(_name);
mailMessage.To.Add(new MailAddress(destEmail));
mailMessage.Subject = "测试主题";
mailMessage.Body = "测试内容";
mailMessage.Priority = System.Net.Mail.MailPriority.High;
SmtpClient client = new SmtpClient();
client.Host = "smtp.xxx.com.cn";
client.Port = 465;
client.EnableSsl = true;
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.UseDefaultCredentials = false;
client.Credentials = new NetworkCredential(_name, _pass);
ServicePointManager.ServerCertificateValidationCallback = delegate (Object obj, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors) { return true; };
client.Send(mailMessage);

 

异常提示：无法从传输连接中读取数据: net_io_connectionclosed。

 

方法二：

System.Web.Mail.MailMessage mmsg = new System.Web.Mail.MailMessage();
            mmsg.Subject = title;// "zhuti1";//邮件主题
            mmsg.BodyFormat = MailFormat.Html;
            mmsg.Body = body;// "wqerwerwerwer";//邮件正文
            mmsg.BodyEncoding = Encoding.UTF8;//正文编码
            mmsg.Priority = System.Web.Mail.MailPriority.High;//优先级
            mmsg.From = from;//发件者邮箱地址
            mmsg.To = to;//收件人收箱地址
            mmsg.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate", "1");
            mmsg.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusername", username);
            mmsg.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendpassword", password);
            mmsg.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpserverport", 465);//端口
            mmsg.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpusessl", "true");
            System.Web.Mail.SmtpMail.SmtpServer = smtp;//ssl://smtp.xxx.com.cn 或 smtp.xxx.com.cn 都不行
            SmtpMail.Send(mmsg);

 

异常提示：与服务器的传输连接失败。

 

补充方法三: