Not receiving external mail after temporary firewall install

So the skinny is – Our company firewall failed on Friday and in order to provide a temporary solution until we receive the new firewall tomorrow, I setup an extra linksys firewall/router that was available. A WRV54G model that was functioning previously.

After setting it up, and forwarding smtp ports to the right IPs, we can send mail externally, but can’t receive. Any thoughts? Much thanks.