问题如下
System.Net.Mail.SmtpException: Failure sending mail.
---> System.InvalidOperationException: Asynchronous operations are not allowed
in this context. Page starting an asynchronous operation has to
have the Async attribute set to true and an asynchronous op
甭理他什么页面需要异步，直接把发邮件代码仍到 Task.Run() 里面执行妥妥的完事儿 ：
Task.Run(()=> {
SendMailCodes();
});