What features are you looking to use in Outlook Email, Calendar, shared, contacts, and such?
the reason I ask is you will most likely need some sort of in-house server and your answers will determine the server OS and software used i.e Microsoft, Linux, MS Exchange, sendmail or NAS.

Do you already have a server?

If you are looking to do only file sharing you can do this without a server and use peer to peer file sharing


Jim