When a user sets their email address, they are provided with the option to verify the email address which they would use if they forget their password.
When they click on the Verify Email button, they will be sent an email with a secure link.
When they click that link, they confirm they have control of the email address and the system will set the Verified flag to True.
If a user has an email address that is not within the allowed email domains, the verified flag will be set to False. And the user will have to set a new email address and re-verify their email address.