As I told in the expirienced phorum before, there are packages only available for debian. Under Redhat you can run a test-version in a changeroot-system. You can download it as a tarball (ca. 40 MB) but you have to build the changeroot first.
There is a 5-client Version of the bill-workgroup-server available from easygate.
If you want to use it with outlook, you would need commercial clients at 39 $ each.
Karl