When I first started photography for Forgotten New York in 1998 there were still a number of these small mailboxes mounted on telephone poles, or even proprietary concrete posts, scattered in outlying areas around town, such as this one on West 254th Street in Riverdale, Bronx. In former years they were also mounted on castiron lampposts.
Not one of the mailboxes featured on the page I devoted to them in 1999 is still in place today!
These boxes had just a small slot at the top and could tale envelopes only. Packages may have begun to take up more of the total volume of mail, so these boxes were gradually replaced.