Thanks you Mr Zhang. Finally able to test out iRedMail properly. The installation is very simple. Once installation completed you can send and receive email (internal and external)from the original domain. The only problem is the virtual domains you going to setup. Administrators need to setup A and MX on all the virtual domains' DNS to point to the iRedMail Server Domain or IP address in order to receive external email.
And it has come to my attention that I need to do a power cycle on my VPS every hour or two in order to receive email from other servers on the globe and there is a delay of 20 minutes or more to receive clam. Does Pro version comes with life time support as well?