邮件发送

using System.Net.Mail;public partial class _Default : System.Web.UI.Page 
{
    protected void Page_Load(object sender, EventArgs e)
    {    }
    private bool SendMail(string strSend,string strReceive,string strSubject,string strContent)
    {
        try
        {
            MailAddress from = new MailAddress("[email protected]");
            MailAddress to = new MailAddress("[email protected]");
            MailMessage message = new MailMessage(from, to);
            message.Subject = strSubject;
            message.Body = strContent;
            message.SubjectEncoding = System.Text.Encoding.UTF8;
            message.BodyEncoding = System.Text.Encoding.UTF8;
            SmtpClient client = new SmtpClient();            client.UseDefaultCredentials = true;
            client.Credentials = new System.Net.NetworkCredential("[email protected]", "lidong19891029");
            client.DeliveryMethod = SmtpDeliveryMethod.Network;
            client.Host = "smtp.sohu.com";            client.Send(message);            return true;        }
        catch
        {
            return false;
        }
    }
    protected void btnSend_Click(object sender, EventArgs e)
    {
        bool flag = SendMail(txtSend.Text, txtReceiver.Text, txtSubject.Text, txtContent.Text);
        if (flag == true)
        {
            Response.Write("<script>alert('发送成功!');</script>");
        }
        else
        {
            Response.Write("<script>alert('发送失败!');</script>");
        }
    }
    protected void btnExit_Click(object sender, EventArgs e)
    {
        Response.Write("<script language:javascript>javascript:window.close();</script>");
    }
}
运行   发送邮件时都是发送失败  
单步运行时在catch那提示“事物失败，服务器响应为: 5.7.1 <[email protected]>: Sender address rejected: Access denied”  谁知道怎么回事啊