rcron.php is for when you cannot run cron on the webserver. Since you can, you should use the cron.php.If you have configured your email properly and you are running cron and not seeing emails getting picked up then you should be seeing an error somewhere (in the osTicket Admin panel -> Dash board -> System Log, or php error log, or the email servers auth logs, or in mysqls logs). Since your running CentOS I feel inclined to ask if you are running selinux, as that regularly causes issues for people here.