Step 1. Clean mailbox and post.
Since you’re working with an old, grimy mailbox you should definitely clean both the mailbox and post. I just used a hose to rinse them off and then wiped them down with a wet paper towel. If your mailbox has rust, you should scrape that off first as well.
Step 2. Spray both mailbox and post with outdoor spray paint.
Once the mailbox and post are clean, you can get them painted. I gave them a few coats of outdoor spray paint.