asp.net System.Net.Mail 发送邮件

163.com的邮箱在早期申请的是支持的，后面申请的都是不支持。
21cn.com似乎现在已经放弃了smtp支持，可能只有缴费用户才可以。
qq.com的邮箱需要在用户帐户里面设置。

MailAddress from = new MailAddress("sosuo8@sina.com");
MailAddress to = new MailAddress("ahuinan@21cn.com");
MailMessage message = new MailMessage(from, to);
message.Subject = "阿会楠的来信";
message.Body = "你好！测试而已";
SmtpClient client = new SmtpClient();
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.Port = 25;
client.Host = "smtp.sina.com";
client.Credentials = new System.Net.NetworkCredential("sosuo8@sina.com", "123");
Response.Write("发送一份邮件到" + to.User + "," + to.Host +"," + client.Host);
client.Send(message);

using System.Net;
using System.Net.Mail ;