At this time, there is no built-in option for restricting an email address from registering to your site. However, you can try and use this third-party plugin for this purpose. Restrict Usernames Emails Characters plugin allows you to Restrict a particular or certain username, email addresses or symbols, or email from specific domain names in the form registration when registering for your site. Learn more by visiting these helpful links:

• https://wordpress.org/plugins/restrict-usernames-emails-characters/
• https://www.wpbeginner.com/plugins/how-to-restrict-usernames-in-wordpress/