dumb USPS mail question- outgoing mail door slot?

Ives 620 Letter Box Plate Mail Slot for Doors door mailbox slot front door mail slot Glossy black wooden front door with a brass ring doorknob and matching knocker finished with a brass mail slot A blue arch front door door with round slot re4 Total Slot Dimensions: 13 in W x 4 in H; Door Dimensions: 10 in W x 2 in H; Weight: lbs; Stainless Steel Finish; Mail Slot Sleeve Sold Separately

door mail slot blocker Discount Door features a selection of mailboxes, mail slots and numeral plaques in quality architectural finishes