Basically, masonry is talking about any material that's put together in units and bound as well as what is called mortar. Mortar is at short, the "glue" because of these sorts of things. There are a many different materials which can be used in brick in mailbox, including granite, brick, https://www.xaphyr.com/blogs/1221684/Brick-Mailboxes-Classic-Curb-Appeal-with-Lasting-Durability