MVCMailer SendAsync() 因 Amazon SES 失败

如果我将 Send() 与 MVCMailer 一起使用，我的 SES 工作正常，但 SendAsync() 显示下面的错误消息，有人知道解决此问题的方法吗？谢谢！

System.Net.Mail.SmtpException: Failure sending mail. ---> System.InvalidOperationException: An asynchronous operation cannot be started at this time. Asynchronous operations may only be started within an asynchronous handler or module or during certain events in the Page lifecycle. If this exception occurred while executing a Page, ensure that the Page is marked <%@ Page Async="true" %>.
   at System.Web.AspNetSynchronizationContext.OperationStarted()
   at System.ComponentModel.AsyncOperation.CreateOperation(Object userSuppliedState, SynchronizationContext syncContext)
   at System.Net.Mail.SmtpClient.SendAsync(MailMessage message, Object userToken)
   --- End of inner exception stack trace ---
   at System.Net.Mail.SmtpClient.SendAsync(MailMessage message, Object userToken)
   at Mvc.Mailer.SmtpClientWrapper.SendAsync(MailMessage mailMessage, Object userState)
   at Mvc.Mailer.MailMessageExtensions.SendAsync(MailMessage message, Object userState, ISmtpClient smtpClient)
   at MVCWebsite.Helpers.AccountHelper.RegisterNewUser(BaseDBContext db, AccountViewModelForReg VM, Boolean isCaptchaValid, Boolean modelValidity) in c:\Users\William-Business\Desktop\TWB\TWB Central\Projects\AwesomeSauce\AwesomeSauce\Helpers\AccountHelper.cs:line 316
   at MVCWebsite.Controllers.AccountController.Register(AccountViewModelForReg VM, Boolean captchaValid) in c:\Users\William-Business\Desktop\TWB\TWB Central\Projects\AwesomeSauce\AwesomeSauce\Controllers\AccountController.cs:line 308
   at lambda_method(Closure , ControllerBase , Object[] )
   at System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters)
   at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass42.<BeginInvokeSynchronousActionMethod>b__41()
   at System.Web.Mvc.Async.AsyncResultWrapper.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _)
   at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.End()
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass37.<>c__DisplayClass39.<BeginInvokeActionMethodWithFilters>b__33()
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass4f.<InvokeActionMethodFilterAsynchronously>b__49()
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass4f.<InvokeActionMethodFilterAsynchronously>b__49()
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass37.<BeginInvokeActionMethodWithFilters>b__36(IAsyncResult asyncResult)
   at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.End()
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethodWithFilters(IAsyncResult asyncResult)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass25.<>c__DisplayClass2a.<BeginInvokeAction>b__20()
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass25.<BeginInvokeAction>b__22(IAsyncResult asyncResult)

此错误是设计使然。您可以全局关闭此功能：

<appSettings>
  <add key="aspnet:AllowAsyncDuringSyncStages" value="false" />
</appSettings>

参考http://msdn.microsoft.com/en-us/library/hh975440.aspx

其他需要考虑的事情是使用任务在后台执行异步，将其与 ASP.Net 使用的调度程序解耦。使用此方法，您不需要更改 appSetting。

using Mvc.Mailer;
...
public ActionResult SendWelcomeMessage()
{
    Task.Factory.StartNew(() => UserMailer.Welcome().SendAsync());
    return RedirectToAction("Index");
}

Edit

启用AllowAsyncDuringSyncStages 或使用任务并行库都有潜在的缺点。使用 AsyncController 没有任何缺点。感谢@StephenCleary 对我的答案提出质疑。

public class HomeController : AsyncController
{
  public void SendMessageAsync()
  {
    var client = new SmtpClientWrapper();
    client.SendCompleted += (sender, args) => 
      AsyncManager.OutstandingOperations.Decrement();
    AsyncManager.OutstandingOperations.Increment();
    new UserMailer().Welcome().SendAsync("", client);
  }

  public ActionResult SendMessageCompleted()
  {
    return View();
  }
}