Cpanel, php, Prestashop: faster mail() function with delivery mode

Hi,
I want to ask how to set the DeliveryMode on cpanel to send email to prestashop faster, and currently takes too long just to process the order.
I was trying to set the Background of deliveryMode php but the result is always the same. Can anyone help me and tell me how to set it correctly? Or it could be that overrides this parameter prestashop?
Thank you.