a private box for delivery of mail
"The courier placed the package directly into the locked mailbox at the end of our driveway."
public box for deposit of mail
"The postman emptied the red mailbox after collecting letters from the neighborhood."
A box into which mail is put
"The postal worker sorted the letters from the mailbox before heading back to the truck."
In plain English: A mailbox is an outdoor box where you put letters and packages so mail carriers can pick them up to deliver to your house.
"I left the letter in my mailbox for the postman to pick up later today."
The word mailbox is a straightforward combination of the words mail and box, created to describe a container specifically designed for holding letters. It entered English as a practical compound term reflecting its function rather than undergoing any significant shift in meaning over time.