The stupidest ( I know that’s not a word) rule I know is one from Barclays Bank.
For over ten years ( since I bought my house). I have periodically received letters for the previous owner who left no forwarding address. I marked the first few ‘Return to sender, Not at this address’
When they kept coming I opened one to check it was nothing important, it wasn’t, so I rang Barclays and explained I was the new owner and had been returning letters for years,even writing in the envelope that I was the new owner/occupiet.
I was told that the Barclays Legal Dept require them to use the last known address.
And they have continued to do so to date despite me telling them I will no longer return mail to them. It goes in the recycling so at least not wasted. .