This piece from 2013 [https://ellenbrown.com/2013/09/23/what-we-could-do-with-a-po...] showed up on HN just over a year ago. [https://news.ycombinator.com/item?id=23911696]
Edit: quote from Brown:
"Postal banking systems are also ubiquitous in other countries, where their long record of safe and profitable public banking has proved the viability of the model.... The leader today is Japan Post Bank (JPB), now the largest depository bank in the world.... Rather than using its deposits to back commercial loans as most banks do, Japan Post invests them in government securities."