The term 'Mailbox FEATURE' can be broken down into two words, 'Mailbox' and 'FEATURE'. The word 'Mailbox' is a receptacle for receiving mail, usually located outside of a house or other building. The word 'FEATURE' refers to a distinctive attribute or element, often one that is prominent or important. The crossword solution for this term is 'SLOT', which is a narrow opening or aperture in a machine or container, used to insert something. In the context of a mailbox, a SLOT is the opening where mail is placed. Therefore, the term 'Mailbox FEATURE' refers to the SLOT in a mailbox where mail is inserted.