Classroom Keepers 30-Slot Mailbox

Dixon Ticonderoga Company Classroom Keepers 15-Slot Mailbox EA Classroom Organizers Easy to assemble and designed to hold a variety of materials

I could also find the word letterbox in the dictionary which seems to be used mostly in UK meaning both a mail slot and a postbox According to

slot bank neo Shop Classroom Keepers 30 Slot Mailbox, 31-58 x 12-34 x 21 Inches at Target Choose from Same Day Delivery, Drive Up or Order Pickup

slot kuda Order a 9-slot teacher mailbox that can also be used to organize and store paperwork, or opt for a jumbo 27-Slot Mail And Supplies Center