Forward domains email to IP?

I have a email server that is off on another network.

I want everything from domain.com to be forwarded to an ip address, which is
the actual email server.

No MX records are in place, except for the main records pointing to the two
primary email servers.

So the third box involved in this does not have an actual MX record, and nor
do I want it to have one. All emai will bounce through the other two boxes
and make their way to the box which only has an ip address associated with
it. I suppose it would be easy enough to create a DNS entry pointing to it,
but I do not want any MX records setup for the box.

Thanks,
Tom W.