Just seconds after I submitted my last response it dawned on me to restart ISPConfig...
After running '/etc/init.d/ispconfig_server restart' the new domain now is browsable!
One small issue, I can send Email from the new domain successfully but when I attempt to send Email to the new domain I receive the following error from ThunderBird.
An error ocurred while sending mail. The mail server responded: 5.1.1
<email@example.com>: Recipient adress rejected: User unkown in local recipient table. Please check the message recipients and try again.
I have tried 3 different addresses which exist under this account with the same result.
Thank you very much Till