HubSpot automatically validates email addresses as they are entered on your HubSpot forms. This default functionality helps to prevent spam form submissions. If you or your customers attempt to submit a form with a fake or outdated email address, an error message will be displayed beneath the email field.
If you are seeing the message "Please enter your business email address. This form does not accept addresses from domain.com", your email field is likely set to not allow submissions from free email providers. Read more here.