Email Domain at Signup

Hi all,
I am making a webpage that is for students, and needs to be restricted from the world. Is there any way to make sure that new users have a certain domain associated with their account, for example: john.doe@school.org, where school.org is required for the user to have in their email?

If there is a plugin, that’s great. If it requires editing the php, is there a way to do it without making wordpress fall apart?

Thank you so much!
Wilson