Under the domains, you can specify the email domains your company is using.
If a new user registers with such a domain name, the administrator will get a notification and can quickly add that user to the account.
The user will see a message informing him about this and ask him to wait for approval. This mechanism is disabled, for example, gmail.com and hotmail.com (in total nearly 10.000 of those free email provider and internet service providers).
Go to the [Company Account] settings, and then: