To try
Finally I found how to build something similar to Win NT Domain and M$ Exchange but on Linux. Here is a document on how to setup Open-XChange + OpenLDAP + Samba + some other stuff to get the whole thing working. The document is not very complete but I think in many cases this should work.
I think I am going to try this, but first I am planning to test Open-XChange by standalone to see how it works :)