When installing RoundCube webmail I found out that the extension "Fileinfo" (also knows as fileinfo.so) wasn't working or installed and I wasn't sure how to get it fixed. After checking my server I found out that its not even installed or configured to work with PHP and Apache. The settings are already set is my Apache vhost as they are supposed to and if you don't know the settings they you can find it here below. The solution I'm posting here worked very well for me and its probably going to work for you as well. For this solution I'm running a Ubuntu LAMP Server.