Linux eMail Server Script

I'm sure there are any number of open source email server scripts floating around the web, but I don't want just a run of the mill email server script. Undoubtedly, there are many top dog email services world wide. When it comes to these services, I am not interested in competing with them. However, I do want a script that functions with all the bells and whistles as can be found in the best of them. The script has to have a front end and an admin back end complete with an SQL database that is able to handle millions of email addresses as well as all the emails related to each address. Additionally, I want the ability through the admin back end to be able to change the color scheme of the front end. It is imperative that the script be fast and run on a Linux email server system