The 3104 is made of 16 gauge electro-galvanized steel with a durable exterior finish. Its unique design has a large opening for the mail to be deposited and a large rear access retrieval door. This unit does not have an outgoing compartment. However it does come with a flag to be used by the carrier to notify recipient mail has arrived. The locking compartment has a cam lock with two keys. It can be mounted into a wall, pilaster, column or post. Recessed mount comes with trim collar to cover up rough opening. Please allow 5-10 business days to be delivered.