SmtpClient smtp = new SmtpClient(Mail.SmtpName);
            smtp.UseDefaultCredentials = false;
            smtp.Credentials = new System.Net.NetworkCredential(Mail.MailName, Mail.Mailpwd);
            smtp.DeliveryMethod = SmtpDeliveryMethod.Network;            MailMessage mail = new MailMessage();
            mail.SubjectEncoding = System.Text.Encoding.GetEncoding("GB2312");
            mail.BodyEncoding = System.Text.Encoding.GetEncoding("GB2312");         
            try
            {
                mail.From = new MailAddress(Mail.MailAddres);
                mail.To.Add(new MailAddress(Str));
                mail.Subject = Subject.Text.ToString();
                mail.Body = MailBody.Text.ToString();
                mail.BodyEncoding = System.Text.Encoding.Default;
                mail.IsBodyHtml = true;                
                smtp.Send(mail);
            }
            catch (Exception Err)
            {
                Time.Stop();
                if (MessageBox.Show(Err.Message.ToString() + "\n\n是否继续发送?", "出错", MessageBoxButtons.YesNo, MessageBoxIcon.Error) == DialogResult.Yes)
                {
                    ErrNum++;
                    Fg--;
                    MyErr.Text = "错误:" + ErrNum.ToString();
                    Time.Start();
                }
                else
                {
                    Time.Stop();
                }
            }
现在可以正常发送1到31封邮件,为什么发送到31封邮件的时候就报错呢?
一超过31封邮件就报:事务失败。 服务器响应为: sender is rejected: 0,smtp5,wKjJDUEAuwV0JStFfvaQAA=