Okay - did that, restarted apache and still nothing. I can't get to webmail - no websites other than the ISPconfig control panel itself. No webmail interface, no phpMyAdmin.
This is bizarre..... It has been rock solid up until now.
I just had a flash of inspiration and decided to add an entry into my hosts file to direct one of the domains to the internal IP address, and it is working! Now.... where to start trouble shooting this new problem.
At least ISPConfig retains its rock solid reputation with me
Thanks Till for your help with this.