Noticed the 3 different postal box. Overtime the company has made different CHANGEs with the size as well as the color. I am not really sure what the number 3,4,5 means and the picture is a little blurry (sorry) so I can’t read what is written.
This one was built in 1971 in commemoration of the Japan Post 100th year anniversary. I have only found 1 of this kind.
In some areas, you can still find some of the old design ( rounded ). In a way these Postal Box’s design have shown how Japan Post have changed over the years.