Simple way to redirect smtp mail to another s

I have a windows XP (not server) running a Domino server. I am setting up a new server and want to find a simple and flexible way to redirect all incoming mail on port 25 to another server. I have spent many hours loooking for a solution but it seems that the only solutions involves complex proxys that do a lot of processing. I am already using such a proxy ASSP on the new server. It really sounds like a very simple little program