System.Net.Mail.MailMessage mss = new System.Net.Mail.MailMessage();       
mss =new  System.Net.Mail.MailMessage("__@__.com","__@__.com");
mss.Subject = "主题";
mss.Body = "内容";
System.Net.Mail.SmtpClient cl = new System.Net.Mail.SmtpClient("服务器",端口);
cl.Credentials = new System.Net.NetworkCredential("验证用户名","验证密码");
cl.Send(mss)

------解决方案--------------------
 MailMessage mailMessage = new MailMessage();         
           
            string strBody;
             mailMessage.From=new MailAddress("xxxxxx@163.com"); //发送人
             mailMessage.To.Add("xxxxxx@yahoo.com.cn"); //收信人
             mailMessage.Subject="Web order";
          strBody = "<h2>" + ddlMainTag.SelectedItem.Text + "</h2><br>";
          strBody += "<h4>" + tbTag.Text + "</h4><br><hr><br>";
         strBody += "·" + tbAdv.Text;
             sendMail(mailMessage);

           foreach (string bo in c)
           {
              Bodytext = "邮件内容";
           }

          objMl.Body = Bodytext;
          SmtpMail.Send(objMl);  
private void sendMail(MailMessage mail)
     
      {
          SmtpClient smtpClient = new SmtpClient();
           smtpClient.EnableSsl = true;
           smtpClient.Host = "smtp.163.com";
           smtpClient.Port = 465;
           smtpClient.Credentials = new System.Net.NetworkCredential("p_bings@163.com","hacker");
           try
           {
               smtpClient.Send(mail);
              // Label1.Text = "ok";
           }
           catch
           {
               Response.Write("发送失败!");
              // Label1.Text = "false";
           }
       }

------解决方案--------------------
 System.Net.Mail.SmtpClient client = new SmtpClient();
       client.Host = "smtp.163.com";  //郵箱服務器
       client.UseDefaultCredentials = false;
       client.Credentials = new System.Net.NetworkCredential("髮件人郵箱名", "密碼");      
       client.DeliveryMethod = SmtpDeliveryMethod.Network;

       System.Net.Mail.MailMessage message = new MailMessage("髮件人郵箱名", "收件人郵箱名");
       message.Subject = "主題";
       message.Body = "正文";
       //message.BodyEncoding = System.Text.Encoding.UTF8;
       message.IsBodyHtml = true;
       //添加附件
       Attachment data = new Attachment(@"附件地址如：e:\a.jpg", System.Net.Mime.MediaTypeNames.Application.Oct