A mail slot (sometimes calle a letter box) is a mail receptacle designed as an alternative to a mailbox. A mail slot is a hole cut in a door, wall, or garage. The hole is usually covered with a decorative face plate containing a swinging door to allow mail to pass through and to act as a seal when not in use. A mail slot may feature weatherstripping to prevent air from leaking. The mail slot door may be spring loaded or may rely on gravity to keep it closed when not in use. Many mail slots also have a second flap on the inside to offer further protection from the elements. There may also be a small basket or wire cage mounted on the inside of the door to catch the delivered mail.