Hello,
I'm a Network and System Administrator. I've installed so many mail servers, and I believe if provided root ssh access and mysql root password, I can deliver this task in less than 5 hours. From the link you provided, it seems that the mail users should be created as local server users, but I think I'll install this using virtual users, it means users will be created using mysql. Please see my feedback to evaluate my previous works, and shoot me your reply if you want to talk about this further.
Regards,
Aroel