Transparent firewall: rule can use secondary gw if default go down?

[firewire]

I have a production pfsense box configured as a transparent firewall with non-transparent-squid binded on Bridge (interface that have ip).
All works like a charme.

Recently it was added a gateway and i've need to create a failover with pfsense, testing all in lab scenario before changing production.

This is my lab scernario (VMWARE+GNS3) that i'm testing.

LAN (all hosts have gw= 192.168.1.250)
192.168.1.0/24
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PFSENSE (lan<–BRIDGE-->wan)
192.168.1.249 (ip on bridge interface)
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SWITCH--------------
| |
| |
GW1 GW2
192.168.1.250 192.168.1.251

I've enabled gateway switching so if defaulty gw go down automatically http traffic is redirect
on second gw (and go back) and all this in lab scenario seems working.

Now I've a question. With my condiguration, can i create a rule that redirect all outgoing SMTP/POP3 traffic on running gateway in default gw go down?
I've created a Gateway group with priorities, and I've tried to create a rule with advanced field gateway="Gateway Grop" on lan interface (and after on Floating) but without success.
It is not possible or i'm wrong in something?

ThankU in advance.