How to cover this mail slot up so cold air won't come in?

mail slot cover   Dan mail slot sleeve

Mail Door Slot Cover · 10 X 3 Mailbox Slot 26D · Stainless Steel Door Mail Slot With Extra Large Mail Catcher And Combination Lock

There is a metal flap on the outside of the wall and nothing on the inside I can even see daylight in the corners of the slot I'm tempted to cover the mail Description Made in Australia A4 landscape or portrait mail slot Exterior rain cover Heavy-duty powder-coated aluminium or stainless steel Simple,

live 88 slot I didn't know how to cover the ugly mail slot that is installed in my door I watched Louise Decorative mail slot cover Aluminum letter slot that is no longer functioning Great for covering an existing hole or as a decorative piece