Restrict registered User email to Org domains

Hi there. I want to enable users from certain Orgs to self register if their email matches one of the Org domains. I'm using Domain Discovery to do this, and after a user inputs a valid email it is redirected to the Registration form. But then it is possible for the user to change the email inputted into a different one and finish the registration, which makes this a security risk. I believe I can use an Action to solve this but is there another setting? I'm on version v2.55.0
Thanks for the help!