I organize all emails with categories (created by myself) and search folder. Therefore each email is categorized. I miss an option mapping category quickly (quick search by category field) in the category overview dialog (right click in the email overview column).
It would be nice if a search box would be created via the category assignment menu. When a letter is typed into this search box, the suggested category list should shrink to match the letter. If the letter is not in the suggestion list, it should be searched in all created categories.