“超时等待客户端输入”到IIS localhost SMTP服务器

Question

我的Web服务正在将电子邮件发送到IISv6 localhost邮件中继，但是随机出现“超时等待客户端输入”错误。我们在数据中心中有几个虚拟机，它们以相同的方式进行设置，并且它们都会不时出现此问题，因此我认为这与硬件无关。我在SmtpClient.Send randomly causes SmtpException 4.7.0 timeout waiting for client input读过类似的问题，但根据发布者的结论，结论似乎与交换服务器身份验证有关。因为我正在将电子邮件发送到localhost中继，所以我不认为会有这个问题。我的代码没什么特别的

     MailMessage message = new MailMessage();
                message.From = new MailAddress(from);

                foreach (string address in receivers)
                {
                    message.To.Add(address);
                }
                message.Subject = subject;
                message.IsBodyHtml = true;
                message.Body = body;

                SmtpClient smtpClient = new SmtpClient();
                smtpClient.Host = server;
                smtpClient.Port = port;
                smtpClient.EnableSsl = ssl_enabled;

                if (username != "")
                {
                    smtpClient.Credentials = new System.Net.NetworkCredential(username, password, domain);
                }

                smtpClient.Timeout = email_timeout;

                try
                {
                    smtpClient.Send(message);
                    email_retry_attempts = 0;
                    message.Dispose();
                }
                catch (Exception e)
                {
                    Log.Exception(e, e.Message);
                }
                finally
                {
                    // Try and close up the connections
                    smtpClient.Dispose();
                    smtpClient.ServicePoint.CloseConnectionGroup("");
                    smtpClient.ServicePoint.CloseConnectionGroup(smtpClient.Serv‌​icePoint.ConnectionN‌​ame);
                    email_retry_attempts--;
                }