Events Clean Up
Are your Opencart emails are getting sent our twice or more times? The reason could be that you have duplicate events. Possible from when you've upgraded your store and they've become duplicated.
But fear not, this can easily be fixed by running this SQL query (using phpMyAdmin or equivalent).
DELETE FROM `event` WHERE `event_id` IN (SELECT * FROM (SELECT MIN(`event_id`) FROM `event` GROUP BY `code`, `trigger`, `action` HAVING COUNT(`event_id`) > 1) temp)