Originally Posted by Gordon Fox
I am looking at moving some smaller Microsoft SBS clients to LINUX, but need to find an exchange server app for server. Thank you in advance for any insights you can offer.
The answer is probably going to be Evolution:
...which can duplicate the functionality, and may (or may not), work for what you're after. If you're just looking to duplicate functionality, you may be able to piece things together. You can find one of the many Linux Caldav servers to provide calendar functionality...some of which also provide cardav services for contact/address-book functionality. From there, the only missing piece is email, and there are PLENTY of solutions for that.
You could use Evolution or Kmail as clients.