各位大侠帮帮小弟看看这代码为什么不能发送邮件!感激不尽！

Question

string mailSubject = "会员注册确认函";
string mailBody = "您好！您的注册已经成功，您的注册名为：'" + U_name + "'密码为：'" + U_password + "'"; ;
string mailFrom = ConfigurationManager.AppSettings["SendMail"];
  if (MySendMail(mailTo, mailSubject, mailBody, mailFrom))
                {                    Response.Write("<script>alert('发送成功！')</script>"); //发送成功，进行相应处理
                }
                else
                {                    Response.Write("<script>alert('发送失败！')</script>"); //发送失败，进行相应处理
                    return;
                }
public bool MySendMail(string mailto, string mailsubject, string mailbody, string mailFrom)
    {        try
        {
            //邮件发送人地址
            System.Net.Mail.MailAddress from = new System.Net.Mail.MailAddress(mailFrom);
            //如[email protected],初步测试，用[email protected]不行，用163的邮件服务器，就必须用163邮箱的用户名
            //收件人地址
            System.Net.Mail.MailAddress to = new System.Net.Mail.MailAddress(mailto);//如[email protected]
            System.Net.Mail.MailMessage mail = new System.Net.Mail.MailMessage(from, to);
            mail.Subject = mailsubject;
            mail.Body = mailbody;
            //以下设置服务器
            System.Net.Mail.SmtpClient mySmth = new System.Net.Mail.SmtpClient();
            mySmth.Send(mail);
            mail.Dispose();        }
        catch
        {
            return false;
        }
        return true;    }

Answer 1

好像没什么错，我的代码如下：可以正常发送，你看一下吧
SmtpClient client = new SmtpClient();            
            client.Host = txtSMTP.Text.Trim();
            client.UseDefaultCredentials = false;
            client.Credentials = new System.Net.NetworkCredential(txtSendName.Text.Trim(), txtPassword.Text.Trim());
            client.DeliveryMethod = SmtpDeliveryMethod.Network;
            try
            {
                for (int i = 0; i < listBox1.Items.Count; i++)
                {
                    MailMessage message = new MailMessage(txtSendName.Text.Trim(), listBox1.Items[i].ToString());
                    message.Subject = "测试";
                    message.Body = "用自己写的软件发邮件！";
                    message.BodyEncoding = System.Text.Encoding.GetEncoding("GB2312");
                    message.IsBodyHtml = true;
                    //添加附件
                    for (int j = 0; j < listBox2.Items.Count; j++)
                    {
                        Attachment data = new Attachment(listBox2.Items[j].ToString(), System.Net.Mime.MediaTypeNames.Application.Octet);
                        message.Attachments.Add(data);
                    }
                    client.Send(message);
                }
                MessageBox.Show("Email successfully send.");
            }
            catch (Exception ex)
            {
                MessageBox.Show("Send Email Failed." + ex.ToString());
            }

Answer 2

我原来也做过，用163的发163的不行，用GMAIL发给别的邮箱就可以

Answer 3

 client.Credentials = new System.Net.NetworkCredential(txtSendName.Text.Trim(), txtPassword.Text.Trim());
这是关键