Howtoforge shows you how to secure your ISPConfig 3 installation with a SSL cert from SmartSSL

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.

  Securing Your ISPConfig 3 Installation With A Free Class1 SSL Certificate From StartSSL