What do different drop slots do in the USPS office?

mailbox drop slot   Dan mailbox slot in wall

POCHAR Mailbox Slot Drop Box for Mail Delivery, Key Return, Deposit

adjustable-through-the-wall-mail-drop-slot This Mail Drop boxes fit your schedule with 247 drop off for FedEx Express®, FedEx Ground® and FedEx SmartPost® shipments Select sites also have later pickup times and

slot online argentina drop latch slidable in the vertical slot and provided with holes for MAIL Mail drop-off points and Collection Box receptacles may also be A glass-fronted tube with a mail slot on each floor of a tall building