Just like the name implies, these letterboxes are designed to be installed on the wall either externally or internally on your property. A wall letter box is one of the most secure options on the market since they feature a plate at the top for the postman to deliver your mail which is secured in a lockable box underneath. These models of post-boxes can be installed on the wall or can be built-in (depending on the wall), either way, they offer one of the best mail security. https://lifestyletrendsofaustralia.wordpress.com/2023/02/02/a-guide-to-different-types-of-letterboxes-and-their-security-level/