If you have a locking mailbox made out of metal, like steel or aluminum, then you will have to have some kind of paint, or coating on the metal to maintain corrosion. Especially if your curbside locked mailbox is made of steel, then for sure you will need it to be painted or coated.

Powder coating is the process of painting the mailbox with a special method. A very fine powder is disbursed inside of an airtight paint booth. The powder is so fine that the particles of the powder hang in the air. The powder is charged with a positive charge. Then the steel item that needs to be painted is give a negative charge and put in the chamber. The powder particles become electrically attracted to the negatively charged steel and they stick to the steel in a uniform way.

Then the steel is backed in a superhot oven and the paint sticks to the surface. It is then removed from the oven then cools and dries. This is how a locking mailbox (and other steel items for that matter) have a beautiful uniform finish.