|Mailing a package in a Canada Post mailbox|
Mailboxes have been like this for as long as I can remember. Even when I was a child in the 1980s, ever mailbox I saw (some of which, I'm sure, long predated the 1980s) had the large opening for packages.
Which raises the question: why would anyone put a package in a street mailbox? Correct postage for a package varies depending on size and weight, and, even if you could reliably calculate the postage at home, people rarely have a wide selection of different denominations of stamps that would enable them to affix correct postage. Under normal circumstances, you'd have to go to a post office. So why would a person ever put a package in the mailbox?
Of course, in the 21st century, the answer is ecommerce. When returning a product from a website with free returns (and perhaps under other circumstances of which I'm unaware), sometimes you get a shipping label that you can stick on a package and pop it right into a mailbox without having to go to the post office.
But mailboxes were designed to accommodate packages long before ecommerce was a thing! Why? Under what circumstances did people mail packages in street mailboxes back in the day?