I had an unsolved problem installing onto CentOS7, so switched to the recommended OS of Debian 8 which worked a treat. Easy to install, no problems and mail server off and running. The only disappointment was that the Debian installation used Squirrelmail, which looks absolutely terrible. Unless you are from East Germany c.1986 where it probably looked great. The CentOS installation used roundcube which looks lovely. Unless you work for Apple. So my question is, can the webmail client be easily be switched from Squirrelmail (Bad) to Roundcube Mail (Good) without breaking everything?