I want a Microsoft Exchange FREE Alternative + installation

I'm looking for a FREE alternative to Microsoft Exchange, and i need the same bidder to install and set up the application on my linux server (most likely CentOS 6.3), but if it works better on other Distros, please mention it to us. 1) find the right FREE alternative to microsoft exchange server which has features like below. 2) must have webmail which looks professional 3) must work with microsoft outlook, even if it needs a connector 4) must sync all calendar, contacts, emails between server and outlook 5) must be able to share files (like a briefcase folder located on the server) 6) i want to sell seperate accounts to different companies based on their needs, either the ability to limit their quota space per mailbox created, or limit the mailboxes created per client. if it has the option to limit features like the "share files" option, to make it as an option sold separately, that would be great too. 7) full system needs to be setup, FULLY configured on my server, and you must show me how i can create accounts, and how i can get them to use their own domain names (ex: if i own [login to view URL], i don't want email accounts created to be related to my own domain name, but i want to be able to sell email accounts for clients own domains) 8) server must be configured properly to be fully secure against hacking, malware, etc... 9) you must install an SSL certificate for me, I will supply the SSL certificate when you are ready. 10) you must help setup a "fail-over" type of server, where we can have 2 servers setup, both have identical info (as up-to-date as possible), where if one server fails, the next server will take-over, to keep everything almost 100% uptime guarantee. I have checked a few options online, but most free options i found are very limited to the features, and i don't mind purchasing a solution, but if the price is fair, and without limitations (ex: 2users, 10 domains, 15 email accounts, etc...), because with limitations like these, i will not be able to make money, and in that case, there is no use for me to even bother building this system. the best one i found so far is Sogo, but it's missing the "shared-files" feature, unless there is an easy option, some how we can integrate it into Sogo, that would Sogo the most suited email/collaboration software i find so far (which is FREE). your recommendations are highly appreciated, and making sure no cheap webmails like squirrelmail or horde, because those are not considered professional at all. Payment: We will Escrow full agreed payment upton bid award, but no payment will be released until project is 100% completed to our satisfaction. if you are unable to live with this rule, please don't bid. Outrageous bidders, please stay away, as your bids will get either ignored, and/or deleted. Notice to all bidders: if you are showing us previous work you have done, please do not show us any work which is not related to this project at all, we are not interested to see your web design skills, and or graphic design skills, as this is not related to our project. thx and good luck to everyone