Ok Falko, Two things
I set the ISPConfig mx records like such:
mail.example.com >> points to 192.168.1.XX
smtp.example.com >> 192.168.1.XX
pop.example.com >> 192.168.1.XX
imap.example.com >> 192.168.1.XX
The only way the mail works is if I use it outside of the one website on the server (before it is production). Example, when you said to set the MX records at the domain registrar, this allowed me to use Google Apps mail exchange network....working beautifully. But, if I go to the website (which is live) and test the contact us form (which I have used on other sites, so I know the form is set-up correctly and reliable) the mail is not routed to my inbox. So, making sense of it, this indicates to me that ISPConfig is still not set-up correctly (server-side & website), but the registrar MX is.