cd $ROUNDCUBE_HOME/plugins
git clone https://github.com/OpenCSI/roundcube-dspam-plugin dspam
Ensure to load the plugins, and configure DSPAM URL:
$rcmail_config['plugins'] = array('dspam', '..');
$rcmail_config['dspam_url'] = 'https://mail.opencsi.com/dspam/';