Oh yea, come to think of it, when i was setting up the ISConfig according to the instruction manual, i was installing these packages :-
apt-get install apache2 apache2.2-common apache2-doc apache2-mpm-prefork apache2-utils libexpat1 ssl-cert libapache2-mod-php5 php5 php5-common php5-gd php5-mysql php5-imap phpmyadmin php5-cli php5-cgi libapache2-mod-fcgid
on my debian VPS and this message popped up :-
There was no mention of this on the manual, so i pressed ok on the "yes" choice since it was already selected by default.
Could this be why email isn't working properly for me?