I'm a Mandriva user for years. ISPConfig didn't work well with Mandriva so I tried other distro's. So far Debian seemed to be the best choice but now I ran into a new issue. I transfered a mailserver. One user needed 128MB storage space on the Mandriva server which uses the mbox format. That same user needs 535MB disk space on the Debian system with Mairdir. What a difference.