Thanks for all the advise.
I did some extra googling on the email-log messages.
And it all came down to a closed port 25.
Although I had a portforwarding rule on my router and it was reachable from the internet with telnet.
So I thought what happens if I close the port(delete the forwarding rule).
Ha!!! Same error messages in my log.
So I went back to the shop where I bougt the router a few days ago and returned it.
I got a brand new router, installed it, and.... ta ta ta !!! It worked.
All the test mails that were still in my que were send.
Whel thanks anyway, I now have a beatifull ISPCONFIG running on my DEBIAN machine.
thanks for the help all of you, hope to be of any help soon to.