记一次邮件推送的坑，c#基于smtp使用腾讯企业邮箱发送邮件总是失败，超时的原因

首先先贴上代码

try
            {
                MailAddress receiver = new MailAddress("zhan.com", "邮箱");
                MailAddress sender = new MailAddress(WebSettingsConfig.SenderAddress, "PC");
                MailMessage message = new MailMessage();
                message.From = sender;//发件人
                message.To.Add(receiver);//收件人
                //message.CC.Add(sender);//抄送人
                message.Subject = model.Title;//标题
                message.Body = "内容：" + model.Content + "<br> 联系姓名：" + model.SenderName + "<br> 联系邮箱：" + model.SenderEmail + "<br> 电话号码：" + model.SenderPhone;//内容
                message.IsBodyHtml = true;//是否支持内容为HTML
 
                SmtpClient client = new SmtpClient();
                client.Host = "smtp.exmail.qq.com"; //
                client.Port = 587;
                client.EnableSsl = true;//是否启用SSL
                //client.Timeout = 10000;//超时
                client.DeliveryMethod = SmtpDeliveryMethod.Network;
                client.UseDefaultCredentials = false;
                client.Credentials = new NetworkCredential(WebSettingsConfig.SenderAddress, WebSettingsConfig.SenderPassword);
                client.Send(message);
                return this.Json(new ResultU(true, ConstResult.success, "邮件发送成功!"));
            }
            catch (Exception ex)
            {
                LogFile.WriteErrorLog(DateTime.Now + " 邮件发送失败:" + ex.Message);
                return this.Json(new ResultU(false, ConstResult.fail, "邮件发送失败!"));
            }