The "Recipient Email Address" feature allows you to curate a list of email addresses that have the authorization to send emails to the device's email address. Even after approving or rejecting an email, you retain the ability to adjust this list as needed.
The "Member Application Review" setting, when turned ON, requires your manual approval for any applications seeking membership to the device. Conversely, when it's set to OFF, all applications for device membership will be approved automatically.