大家好:

gmail(587 port)是否能大量寄信..因為我用寄信視窗程式(winform)C#迴圈寄,用gmail當smtp server，程式會卡死，所以又修正非同步(asnyc await)，雖然會有點慢，但至少程式不會卡死

但是執行一陣子程式會回覆以下資訊造成中斷，想請問有甚麼方法改善
ServiceNotAvailable 421
SMTP 服務目前無法使用；伺服器正在關閉傳送通道。

用自家公司信箱 25 port算順利 Q_Q

好像587 port用迴圈gmail跟yahoo真的不行大量寄Orz

private async void button1_Click(object sender, EventArgs e)
        {
            try
            {
                SmtpServer = new SmtpClient("smtp.gmail.com");
                SmtpServer.DeliveryMethod = SmtpDeliveryMethod.Network; 
                login = new NetworkCredential("sample@gmail.com", "srcbn"); 
                SmtpServer.Credentials = login; 
                SmtpServer.EnableSsl = true;
                SmtpServer.Port = 587;
                Mymail = new MailMessage();
                Mymail.SubjectEncoding = System.Text.Encoding.UTF8;
                string senderNameb64Enc = Convert.ToBase64String(Encoding.UTF8.GetBytes("aaavvvv"));
                Mymail.From = new MailAddress("sample@gmail.com", $"=?UTF-8?B?{senderNameb64Enc}?=", System.Text.Encoding.GetEncoding("UTF-8")); 
               
                Mymail.IsBodyHtml = true; //是否用html格式
                Mymail.BodyEncoding = System.Text.Encoding.UTF8; 

                string[] formdata = { "sample@yahoo.com" };
                for (int i = 0; i < 500; i++)
                {
                    Mymail.Subject = "aaaqq"+i.ToString();

                    foreach (string email in formdata)
                    {
                        Mymail.To.Add(email);
                        await SmtpServer.SendMailAsync(Mymail);
                        // SmtpServer.Send(Mymail);
                    }
                }
                MessageBox.Show("OK");
            }
            catch (SmtpException ex)
            {
                MessageBox.Show(ex.StatusCode.ToString());

            }
        }