Noun
a private box for delivery of mail
public box for deposit of mail
a numbered compartment in a post office where mail is put to be called for
Source: WordNetletter-box
I became a connoisseur of that nasty thud a manuscript makes when it comes through the letter box. James Herriot
Around 8:30 a.m. on April 10, Proulx says someone brazenly broke into mailboxes in his Mount Pleasant apartment lobby and stole a new Toronto Dominion bank debit card in his letter box. Source: Internet
“Where candidates can do more work is with letter box drops and social media, which will probably play a greater part in this election.” Source: Internet