If you live in an area where your mail is delivered to your home, you are required by the U.S. Postal Service to have a receptacle to receive the mail. Door slots must be at least 30 inches above the floor where they are installed and mailboxes 41 to 45 inches high if you have curbside or roadside delivery. There the regulation ends.
Some developments have their own requirements for mailbox design aside from the USPS, meant to create a uniform and cohesive look to the streets of a neighborhood. Simple black posts with identical black mailboxes or brick surrounds that encase the mailbox and match the brick of your home.
Popular decoration of mailboxes sometimes includes the personality of the owner. It might include painting the mailbox and post the colors of your favorite sports team or a big plastic fish where the mail is delivered into a big plastic fish mouth, or a clever one that has a 6 to 10-foot rod extended above the regulation 41-inch high mailbox, upon which an additional mailbox is attached and labeled Airmail.
Mailboxes become part of the curb appeal (or not) of your home. Keeping your mailbox tasteful, in good repair and blending with the overall look of your home and landscaping is still the best curb appeal if you are selling your home.