The national delivery service. Anything, to anyone, anywhere in school — a book to the library, a Match Attax card to another form room, something you sold on the marketplace. Delivery is free. Couriers are citizens who signed up to run parcels, and the nation pays their wage through the delivery levy.
Free, whatever it is. Tell us which class it's leaving from and which class it's going to — a courier picks it up from there.
Set your usual class once and every delivery to you is addressed there automatically — including things you buy on the marketplace and cards you trade.