C#的异步请求

public async Task SendMailAsync(long userId)

        {

            UserAccount ua = this.appUsersService.GetUserAccountById(userId);

            var user = this.appUsersService.GetAppUserById(userId);

            var mailDetil = "通知信息:<br>领取金额:" + Math.Floor(ua.Withdrawals) + "元<br>用户Id:" + userId + "<br>用户姓名:" + ua.ActualName + "<br>领取时间:" + DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss") + "<br> 用户地址:" + user.Address;

            await HelpTool.SendMailValiAsync("用户取现通知", mailDetil);
        }

在async的方法下，用await调用task方法