More interactions with threads.

Wino.Mail.ViewModels/Collections/WinoMailCollection.cs

@@ -75,6 +75,11 @@ public class WinoMailCollection : ObservableRecipient, IRecipient<SelectedItemsC
         Messenger.Register<SelectedItemsChangedMessage>(this);
     }
 
+    public void Cleanup()
+    {
+        Messenger.Unregister<SelectedItemsChangedMessage>(this);
+    }
+
     public async Task ClearAsync()
     {
         await ExecuteUIThread(() =>

Wino.Mail.ViewModels/MailListPageViewModel.cs

@@ -204,11 +204,14 @@ public partial class MailListPageViewModel : MailBaseViewModel,
         MailCollection.ItemSelectionChanged += MailItemSelectionChanged;
     }
 
-    public override void OnNavigatedFrom(NavigationMode mode, object parameters)
+    public override async void OnNavigatedFrom(NavigationMode mode, object parameters)
     {
         base.OnNavigatedFrom(mode, parameters);
 
         MailCollection.ItemSelectionChanged -= MailItemSelectionChanged;
+
+        await MailCollection.ClearAsync();
+        MailCollection.Cleanup();
     }
 
     private void MailItemSelectionChanged(object sender, EventArgs e)