I did not know that, if you refer to the country I have in mind. Crazy.
Goes in line with the fact that using cash for more then 2000.- is forbidden in Spain and in Italy it's a even lower limit with 1000.-. There are high fines when using cash above those limits. Crazy...
In Spain as far as I know the Banks are sending all your financial data to the tax authority end of the year. So you have zero privacy in your financial life beside using cash in limited amounts.
Let me clarify. I remember that I sent once a packet and it was clearly forbidden to send cash. The postal service has specific services for money. I could not find reliable sources regarding the legality of cash-in-mail in Spain.