Used in multistory buildings for gravity delivery of mail from the various floors to a mailbox in the main lobby, a mail chute is simply a vertical, unpressurized, rectangular tube. With permission of the Post Office, one or more chutes may be installed in office buildings more than four stories high and in apartment buildings with more than 40 apartments.
Usually made of 20-ga cold-formed steel, with a glass front, and supported by vertical steel angles, a chute is about 3 x 8 in in cross section. In the front of the chute, available in a lobby in each story, a slot is provided for insertion of flat mail into the chute.
The mailbox usually is 20 in wide, 10 in deep, and 3 ft high. It should be placed with its bottom about 3 ft above the floor. The mailbox should be placed within 100 ft of the building entrance.
