Configure exim on Debian to redirect mail to another server
I'm having some problems setting up my mail server. I have a mailserver (A)located in a network where port 25 is blocked for incoming connections. Thus, I've configured my server (A) to also listen on port 26 for smtp connections.
But now comes the tricky part: I want another server (B), which does has port 25 openend for the world, to function as a relay. But how do I make exim on B relay mail for server A to port 26 on A?
I've ben looking for a method to exim to do this, as well as an iptables rule for B that simply send all traffic directed to server A:25 to server A:26, but I haven't been abled to find a method for both of these.