You can use the following query to get all emails which don't have any person or org profile associated with it:
SELECT `email`
FROM `sys_accounts` AS `a`
LEFT JOIN `sys_profiles` AS `p` ON ( `p`.`account_id` = `a`.`id`
AND `p`.`type` != 'system' )
WHERE `p`.`id` IS NULL
Thank you Alex, it helps, but like DeDiary, I hope a more user-friendly solution and secondly it is not a solution for turnkey solutions that you propose to avoid this kind of manipulation.
