Each unsubscribe link sent over the email is based on the receiver’s email address and the email type of that particular email template. When a customer clicks on the subscribe link, his email address is added to the unsubscribers list and only for the specific email type. This email address will not receive any emails for this email type, but he can receive emails that are tagged to other email types.
An admin can manually unsubscribe users from all email types by adding the email address. This email address will not receive any emails regardless of the email type.
You can override the subscription status for any email type by using this option shown in the screenshot below. So, if the checkbox is selected for the email type, emails will be sent to the email address even if the email address is added to the unsubscribed list. This is basically an override function useless to send important emails like account emails, and important alert update emails.