Zone
firewall zone new upl0 [uplink]
firewall rule add src 192.168.1.2 dst 192.168.1.3 action accept
firewall rule add src 192.168.1.2 dst 81.3.27.38 action snat 1.2.3.4
firewall rule add src group:Servers dst zone:upl0 action reject
firewall rule add src host:mail01.ipfire.org dst zone:upl0 proto tcp dport 25 accept