You shouldn't ever tell anything which server to forward mail to.
You should be telling it which *address* to forward to, and it should use Mail Exchange (MX) records to determine what machines to send the emails to.
I don't think you're forwarding properly, or you took a wrong turn somewhere!
I use UNIX mailservers and just add a rule in procmail to "echo" my email to my BWC account. I wrote an article about it here: