C# SMTP SendAsync not working

我在使用SendMailAsync时遇到问题。当我将其更改为普通Send时，它可以正常工作。当我使用SendMailAsync时，我得到一个连接超时，并且没有发送邮件。我是不是设置错了？

编辑：1.我更改了变量名！！！2.确切的错误发生在这里await smtpClient.SendMailAsync(mailMessage);它只是挂起，直到连接超时，我得到了"连接超时"的错误描述。返回的状态码是General Error

3. 我现在将表单中的sendEmail称为按钮的onClick事件。await unitOfWork.Instance.SendEmail(...)它是onclick事件中的一行代码

   public async Task SendEmail(List<string> notificationList, string emailSubject, string emailMessage)
           {
               var message = new MailMessage()
               {
                   IsBodyHtml = true,
                   BodyEncoding = System.Text.Encoding.UTF8,
                   Subject = emailSubject,
                   From = new MailAddress(FromEmailAddress),
                   Body = emailMessage
               };
                try
               {
                   foreach (var emailAddress in notificationList)
                   {
                       message.To.Add(emailAddress);
                   }
                   var people = string.Join(Environment.NewLine, message.To);
                   MessageBox.Show(@"from: " + unitOfWork.CurrentSystemUser.Person.Email + "To: " + people);
                   await SendMessage(message);
               }
               catch (Exception E)
               {
                ...
               }
               finally
               {
                 ...
               }
           }
       private async Task SendMessage(MailMessage mailMessage)
       {
           if (!CanSendSmtpEmail) return;
           await SendSmtpMail(mailMessage);
       }
       public async Task SendSmtpMail(MailMessage mailMessage)
       {
           SmtpClient smtpClient = new SmtpClient(SmtpClientHost, int.Parse(SmtpClientPort));
           smtpClient.SendCompleted += (s, e) => {
               smtpClient.Dispose();
               mailMessage.Dispose();
           };
           await smtpClient.SendMailAsync(mailMessage);
           //smtpClient.Send(mailMessage) works fine
       }