New! Mailbox with Key, White, DIY Approximate mailbox size: Height: 11.5cm Width: 16cm Depth: 18cm Slot size: Thickness: 1cm Width: 13cm Opened for inspection. The brown lines in the photos are packaging material. There is a hole in the bottom (opening) where a key can be attached. The slot is horizontal, so the contents are less likely to get wet on rainy days. Photo 8: The curve on the edge has a poor finish.