string from = "webmaster@xxx.cn";
string pwd = "xxxxxxxxx";
string to = user.Email;
string subject = "欢迎加入xxx，请激活您的帐号";
string body = GetEMailBody(user);

SmtpClient client = new SmtpClient();
client.Host = "smtp.xxx.cn";
client.UseDefaultCredentials = false;
client.Port = 25;
client.Credentials = new System.Net.NetworkCredential(from, pwd);
client.DeliveryMethod = SmtpDeliveryMethod.Network;
MailMessage message = new MailMessage(from, to);
message.Subject = subject;
message.Body = body;
message.BodyEncoding = Encoding.UTF8;
message.IsBodyHtml = true;
client.Send(message);