Really? Wouldn't that catch people with `.co.uk` or similar localized domains?
They use a regex such as /[a-z]+(\.[a-z]{2,3}){1,2}/
There’s a lot of bad email validation regexes floating around on the internet. If it’s an older service it may have been written before gTLDs.
I have an address that ends in .fyi and continue to encounter systems that refuse to accept it as a valid domain. It's really frustrating but at least I have a .com that I can enter into those and just forward it.