MVCMailer SendAsync() fails with Amazon SES

Question

If I use Send() with MVCMailer, my SES works fine, but SendAsync() shows the error message below, does anyone know of a work around for this? THanks!

System.Net.         


        

Answer 1

This error is by design. You can turn this off globally:

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

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

Something else to consider is using a Task to do the async in the background, decoupling it from the scheduler that ASP.Net uses. Using this method, you wouldn't need to change the appSetting.

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

---

Edit

Enabling AllowAsyncDuringSyncStages or using the Task Parallel Library both have potential drawbacks. Using AsyncController does not have either drawback. Thanks @StephenCleary for challenging my answer.

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();
  }
}