Hi dfex
The command "show security flow session destination-prefix 192.168.254.1/32" didn't display any sessions so I ran the command to show destination-port 25 which showed some information.
I fired a telnet to port 25 with routing set to use the at-1/0/0.0 interface and then changed the routing to go out the fibre on fe-0/0/1.0 and issued a telnet again. The results are displayed below:
root@srx-110> show security flow session destination-port 25
Session ID: 11544, Policy name: SMTP-OWA/6, Timeout: 1586, Valid
In: 114.134.165.186/2195 --> 219.88.101.197/25;tcp, If: at-1/0/0.0, Pkts: 3, Bytes: 128
Out: 192.168.254.1/25 --> 114.134.165.186/2195;tcp, If: vlan.0, Pkts: 2, Bytes: 204
Session ID: 12428, Policy name: SMTP-OWA/6, Timeout: 1798, Valid
In: 114.134.165.186/2018 --> 219.88.101.197/25;tcp, If: fe-0/0/1.0, Pkts: 2, Bytes: 88
Out: 192.168.254.1/25 --> 114.134.165.186/2018;tcp, If: vlan.0, Pkts: 2, Bytes: 204
Total sessions: 2