[badc0ffee]

But those have been around forever. The newer ones (.shop, .wiki, etc.) are >3 and it makes more sense to me they wouldn't be handled correctly.

[abirch]

I don't know the specifics. I can imagine someone using a regex like

^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{3}$

it worked for the emails that the web dev tried and you have to have a valid email address to file a complaint.