c#发邮件稳定性问题问题

请各位大侠帮忙看看，因为下面的代码不是非常稳定。希望大家指点下，在线等……for (int i = 0; i < 50; i++)
            {
                
                OnTimer(i);
                Console.WriteLine(i);
                Thread.Sleep(5000);
            }
public static void OnTimer(int i)
        {
            try
            {
                //定义信息
                string user = "[email protected]";//[email protected]  [email protected]
                string passWord = "hao13727815158";
                string receivePerson = "[email protected]";
                string sendTheme = "测试" + i;
                string sendText = "测试文";
                    SmtpClient client = new SmtpClient("smtp.qq.com");
                    client.Credentials = new System.Net.NetworkCredential(user, passWord);
                    client.DeliveryMethod = SmtpDeliveryMethod.Network;                    MailMessage mmsg = new MailMessage(user, receivePerson);
                    mmsg.Subject = sendTheme;
                    mmsg.SubjectEncoding = Encoding.UTF8;
                    mmsg.Body = sendText;
                    mmsg.BodyEncoding = Encoding.UTF8;
                    mmsg.IsBodyHtml = true;
                    mmsg.Priority = MailPriority.High;
                    client.Send(mmsg);  
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }按照上面的代码。测试之后发觉非常不稳定，发了50封才收到25封！