Notification grouping requires Android 7.0

app/src/main/java/eu/faircode/email/FragmentOptionsNotifications.java

@@ -558,6 +558,7 @@ public class FragmentOptionsNotifications extends FragmentBase implements Shared
             }
         });
 
+        swNotifyGrouping.setVisibility(Build.VERSION.SDK_INT >= Build.VERSION_CODES.N ? View.VISIBLE : View.GONE);
         swNotifyGrouping.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
             @Override
             public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {