I've had to locally override some JS on the client-side and hoped their backend validation was a lot more sane. The frontend validation logic was limiting the TLD to minimum of two characters and max of four ({2,4}). I use a .email TLD for sites that I don't want to give my personal email.

If you're using Chrome (65+), you can easily bypass any validations/logic by using local overrides (https://developers.google.com/web/updates/2018/01/devtools#o...). As marcolussetti said, it's worth trying out.