I'm still not understanding your configuration here. Your servers can't have a "network" assigned to them. The network refers to a range of addresses in a network. So if you have a network of 192.168.10.0 then your email server has an address on that network like 192.168.10.1 through 254.
As for your discription of the firewall (router), I'm afraid you just complicated me a bit. An internal IP and external IP address of which both have to have 4 octets assigned. So 192.168.254:441 is an invalid description of your firewall's internal IP.
This is what you are describing to me in the virtual world:
[INTERNET]--[SONICWALL ROUTER 192.168.10.0]---[EMAIL SERV (192.168.10.1)]
| Same Router
|-[SONICWALL ROUTER 192.168.11.0]---[EMAIL SERV BACKUP (192.168.11.1)]
This is how you have set it up right? Sorry if we are taking steps backward. I have to understand what your setup is before I can formulate a plan.