I've got a server with exim4 and a smarthost in front of it, the use of the smarthost is mandatory, the university closed down port 25. However, on IPv6 this port is open. So when the receiving server has an IPv6 address I could send it directly.
So my question is, how can I let exim make a routing decision based on the IP-address, or try IPv6 first and if that doesn't work use the smarthost.