Add isolated gateway.

[dcol]

Hi all,
I am now running 2 OPNsense boxes where box one has a DHCP WAN, and a LAN (192.168.100.0/24).
Box two has a static WAN and LAN (192.168.20.0/24). Both work fine right now.

My goal is to eliminate box two since the only task on that box is to NAT port 25 to the email server on the LAN.
This email server has another NIC which connects to the LAN subnet on box one (192.168.100.5).

I tried moving the box two WAN to box one WAN2. Then using a NAT rule on box one to forward WAN2 port 25 connections to the email server. This does not work.
The WAN2 gateway is online. I can ping WAN2.
The box one LAN rule is matched to the one from Box 2
WAN2   TCP   *   *   WAN2 address    25    192.168.100.5    25

I assumed all I needed to do was install the WAN2 interface/gateway on OPT1, then NAT WAN2 to port 25 to the email server.
Am I missing something? Is there something else I need to do to isolate these gateways?
Please reply if you need more info.