Please drop the letter into the letter-box.

请将信投到信箱里。

Yesterday she found this leaflet in her letter-box.

昨天她在信箱里发现了一张宣传单。

The key which you posted was in the locked letter-box too.

你邮寄的钥匙也在锁着的信箱里。

The postman tried to crush the packet through the letter-box.

邮递员使劲把信件塞进信箱里。

There are two collections a day from this letter-box, ie The postman empties it twice a day.

这个信筒每天收信两次（邮递员每天取走两次）。