There was a requirement in 2014 (I think?) and recently they updated it in 2017. I think people that weren't meeting guidelines started getting notices from registrars around that time. A few clients of our had this happen to them from everyone from GoDaddy to Network Solutions to NameCheap. Some organizations that had their emails set to go to a person that no longer worked at the company were having their domains suspended...but it was all because of ICANN.