While processing mailItems, an add-in opens and closes the mailitems and creates a visual pollution. As far as I found out there is now such method for Outlook. I tried:
newItem.Display(false);
newItem.GetInspector.WindowState = OlWindowState.olMinimized;
These methods don't give a result like a screenUpdating in Excel. Maybe there is any trick to switch off screen updating?
The method Display(false)
opens mailitem and then closes it, that's why creates a visual pollution. There is no need to use this method to prevent open the mailitem.