MainWindow: Delay email sending

Elwig/Windows/MailWindow.xaml.cs

@@ -958,6 +958,7 @@ namespace Elwig.Windows {
                             m.EmailAddresses.OrderBy(a => a.Nr).Select(a => a.Address).ToArray(),
                             subject, docs.Select(d => d.Title).ToArray()
                         )]);
+                        await Task.Delay((int)(App.Config.SmtpWait * 1000));
                     }
                 });