c#发邮件

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Web.Mail;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void sub_Click(object sender, EventArgs e)
    {
        MailMessage MyMail = new MailMessage();

        //收信人
        MyMail.To = Request.Form["mailto"];
        //抄送
        MyMail.Cc = Request.Form["mailcc"];
        //密送
        MyMail.Bcc = Request.Form["mailbcc"];

        //附件
        if("" != Request.Form["mailattachments"])
            {
                MailAttachment myAttachment = new MailAttachment(Request.Form["mailattachments"], MailEncoding.Base64);
                MyMail.Attachments.Add(myAttachment);
            }

        //发信人
        MyMail.From = Request.Form["mailfrom"];
        //标题
        MyMail.Subject = Request.Form["mailsubject"];
        //信体
        MyMail.Body = Request.Form["mailbody"];
        //优先级
        MyMail.Priority = MailPriority.Low;

        //设置支持服务器验证
        MyMail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate", "1");
        //设置用户名
        MyMail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusername", Request.Form["mailuser"]);
        //设置用户密码
        MyMail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendpassword", Request.Form["mailpassword"]);

        SmtpMail.SmtpServer = Request.Form["mailsmtp"];
        SmtpMail.Send(MyMail);

        Response.Write(Request.Form["mailto"]);
    }
}

运行有错误，SmtpMail.Send(MyMail);这个地方，请问怎么解决！
--------------------编程问答-------------------- 什么错误，具体的错误信息？ --------------------编程问答-------------------- 提示什么错误
换换其他邮箱
--------------------编程问答-------------------- 参考这个：

Easy SMTP Mail Using ASP.NET 2.0

--------------------编程问答-------------------- 楼主的信息不全，没法解释！

补充：.NET技术 ,  C#