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 ;