2 way email forwarding script for linux ?

Does anybody know of a script that will forward both ways in a email conversation so real primary email stays private ? Normally it is just one way that i knowq but i`m having a hard time finding a script to do it, if a domain is needed it`s ok, no problem there. I could pay for a service online but why bother when the intent is to remain private. Hopefully free / open source.