[ Thanks to Falko
Timme for this link. ]
“This tutorial shows how you can use a free Class1 SSL
Certificate from StartSSL to secure your ISPConfig 3 installation
and get rid of self-signed certificate warnings. The guide covers
using the SSL certificate for the ISPConfig web interface (both
Apache2 and nginx), Postfix (for TLS connections), Courier and
Dovecot (for POP3s and IMAPs), and PureFTPd (for TLS/FTPES
connections). If you’ve installed monit and use HTTPS for its web
interface, I will show you how to use the StartSSL certificate for
it as well. This guide assumes you use Debian or Ubuntu; the
principle is the same for other distributions supported by
ISPConfig 3, but paths might differ. “