I worked for an Australian insurance company and we physically DDOSed a poor man's real mailbox with printed policy documents as we used their address during e2e testing and we mistakenly didn't put a testing flag somewhere.
I lost a Nationwide Building Society account I've had for forty years last year because the bank bought some extremely poor online-ID-verification system.
The bank forgot it had customers in a Crown Dependency. It forgot those countries issues their own ID, their own passports, their own drivers' licences. It forgot it closed its branches in those countries: it told me I had to go into my branch. My nearest branch is a £200 airfare away. It was not paying, naturally.
The crappy online-verification tool only recognises UK documents. It can't handle Isle of Man ones. They did not think.
The documents pack is like an A4 folder 1cm thick. He received close to 100 in one day. Enough for his mailbox to get full and for the postie to dump most of it on the lawn
Our CTO had to personally apologise to him