disallow list of known bad email providers.

Imagine giving someone your phone number, and having them say you have to get a different one because they don’t like some of the digits in it.

I have seen this nonsense more times than I care to remember. Please don’t build systems that way.

If you’re trying to do bot detection of the like, use a different approach. Blacklisting email addresses based on domain or any other pattern does a poor job of it and creates an awful user experience.