Another method of increasing the rust resistance in your curbside locking mailbox is to use two coats of paint, a primer coat and a powder coat.
Most steel locking mailboxes today on the market do not use a primer coat, they only use a powder coat over a galvanized steel. While the galvanization does provide some rust protection, it can still rust at the cut ends and the welds. If a zinc alloy steel is not used, then the next best thing is to use a high zinc content primer coat before applying the powder coat.
Most outdoor steel fencing (decorative type fencing) uses the double painting method. Most mailbox manufacturers should take a page from the book of the fence makers and do a double coat.
The MailCase solves the problem by using the rust resistant high zinc-steel alloy.