When installing ISPConfig 3 using the guide here:https://www.howtoforge.com/tutorial/perfect-server-ubuntu-16.04-with-apache-php-myqsl-pureftpd-bind-postfix-doveot-and-ispconfig/
After initial installation and configuration
When trying to access the webmail at https://YOURIP:8080/webmail/ you get a 404 error. If we select roundcube as our default webmail client
Issue these commands
cat >> /etc/apache2/conf-available/local.conf <<EOF Alias /webmail /var/lib/roundcube EOF
a2enconf local
service apache2 restart