Hi @mike16
Welcome to the Auth0 Community!
My understanding is that you would be looking to restrict signup and login to your application to a specific list of email domains.
An easy implementation of this flow would be to use our Actions feature in order to restrict access based on an allowlist of email domains. Once you establish the domains that you wish to grant access to, you can then add the list to a Post - Login Action so that access will only be granted to domains from the list. Allow me to share some useful Action templates and documentations on the matter:
While Auth0 cannot directly determine the legitimacy of a business, it can be used to limit access to your application based on a list of email domains that you know are trustworthy.
Hope this helped!
Gerald