National Postal Museum
Beginning in the 1950s, many cities offered separate mailboxes for local and out-of-town mail to speed processing. Marketing photo's like this promoted their use to increase efficiency.
The sender writes:
How adorable is this postcard displaying the old Post Boxes here in D.C.?! I might just frame this one, I love it so much!
This is postmarked in 2016 from Washington D.C.
USA stamp 2015