"I never thought the leopards would eat MY face," sobs dude who contributed to the leopard-owned face eating industry.

There has never been a good argument for attempting to filter email addresses based on domain. Check address syntax on interactive forms purely to help users (did they fat finger something). Whatever well-formed address you've got, fire off emails and if they can receive them then it's a legit address. If you want to rate limit signups, then do so per-domain or per-mx, the same way you might limit incoming connections per-ip. That is the extent of guarantee that email provides you - trying to step over that demarc point is a control delusion.

Even outright throwaway domains like mailinator.com - if a user is giving you this type of address, it says more about your own requirement demanding an email address rather than the user themselves.