Install Working Mail Server after Successful Installation of VestaCP

[atorui]

Hi! I have installed VestaCP successffully on Debian 8.6, opting 'MAIL' in 'Advanced Install Settings' on the Homepage to 'no', due to lower RAM I had at that time. Now as I have upgraded my RAM, I want to have mail functionality on my VestaCP installation. How do I do that and what to configure? Thanks!