Replace a mailbox latch by purchasing a replacement latch set kit. These kits are available on websites such as Amazon.com and eBay.com. Ensure the kit is usable with your current mailbox. Another option is to replace the mailbox door with a new door that already has a latch installed.
A flat head screwdriver is the only tool needed to replace a broken mailbox latch with a latch set kit. Open the mailbox door and support it with your left hand to ensure it does not bend too far when pressure is applied. Next, using the screw driver, bump the molded lip of the bracket clip toward the open box to free the broken pieces.
To install the new latch, place the latch on the front of the mailbox door, threading the pegs through the holes on the door from front to back. Hold the new latch in place and lower the mailbox door until it is completely open. Support it with the same hand while simultaneously placing the new clip over the second peg from the back side of the door with the other hand. Slide the clip forward so it hugs both pegs and secures the new latch.