RoundCube installation on Debian 8 (Jessie)

This tutorial shows the installation of the latest RoundCube webmail on Debian 8. Roundcube is an easy to use webmail client with IMAP and SMTP support that can be extended with plugins. On Debian 7, RoundCube was available as .deb package, it was not the latest version but at least it was easy to install with apt. For the current Debian release, there is no RoundCube package available anymore so I’ll describe the installation from source here. This tutorial contains an optional chapter that describes the steps to connect RoundCube ith the ISPConfig 3 Hosting Control Panel.