I vaguely recall encountering a service that only accepted addresses from a whitelist of big providers (Gmail, Yahoo, Outlook, etc.), even @icloud did not qualify.
I've never once run into a service with such a restriction, but I can imagine someone being that short-sighted. I have seen services that only support "log in with Google or Facebook", which is comparably terrible.
Who? Never heard of them, and it sounds like there's a good reason for that.