The thing is: I couldn't figure out how to do this with Apache so now I use aolserver to handle the domain names...
I'm not 100% sure about this though, because I don't know how to check that. But when I turn off apache, everything keeps working fine.
However I would be saved if I could get openacs to return the URL from the address bar. But if I type in "www.mynewdomain.nl" in the address bar the function [ad_conn location] returens "www.myolddomain.nl"