znguissi: Believe me when I say, I understand your pain. Everything I've ever configured in Linux has come at a great price of time.
I don't use ebox for mail. Its actually one of the few things I don't like about it. I think the interface to mail is hindering. For me, I don't know how anyone could configure an enterprise mail server from that interface. If I was going to setup mail from ebox, I would do it as I said before. I would go to /etc/postfix and edit main.cf for my needs. Sorry, I really understand.
Its really not as bad as it sounds. I know the first time you look at the config file its bewildering. However, if you decide to take it on, I can provide steps for getting a straightforward no frills email server up and running. I would be willing to do that because others have done it for me many years ago. If not, perhaps one of the other members has done it and will take the time to help you use the gui.
Good luck