Clean the mailbox with soap and water. You can also scuff it up a little with extra fine sandpaper or use a paint prep surface cleaner to make sure the paint adheres.
Wrap flag in painter’s tape.
Once the mailbox is dry, use a spray paintmeant for metals.
Then spray the whole mailbox white, black, or with the color of your choice. See spray painting tips above.
Wait for each layer to dry, and repeat until you are happy with the even appearance of color.
Notes
If you only want one color for your mailbox, then go ahead and put it back up.
If you want a decorative mailbox idea, you can see how we used painter's tape and different layers of spray paint for a fun look.