what is your question?
Water-based paints of course are easy to use, but on a mailbox you’re going to have to get something that’s going to dry into an enamel- like finish, like an exterior latex enamel. Or it will attract rust and fade.
If your artistic hand is a little shy of what you’re envisioning, I would make a template or a stencil, or even print something & then use old fashioned carbon paper to trace-transfer the image.
https://www.hometalk.com/2324569/painted-mailbox Nina, hope this helps you
Nina: maybe this will help
...then you can use a stencil on the top for an easy design!!!
Good luck. Have fun!