If you want to allow any user to access your academy if they have a specific email domain, here is how.
To allow an email domain to grant access to everyone with that domain to your academy, you will want your academy to be private. This will make it so that if someone who you haven't invited comes to the academy, they will have to request access in order to take training.
To turn on, make the academy private, you will simply want to go into the general settings and check the "make academy private" option.
After enabling this, you will want to click the invite users button either in the same area or on the Users section in the settings.
Once you click the invite users button, a screen will show up. Click the "Allow Email Domains" at the top center, enter the domain in the text box, and click "Allow"
And that's it, you don't need to do anything else now. Once users create an account using that email domain, they will have access to your full academy.