NW5 with SP6a, BM35 with SP3 , new installation

I have a e-mail server in the LAN, a Public IP NAT to it.

the Outbound SMTP-ST exception is NOT working well:

Source: Private
Dest: Public
packet type: smtp-st
source ports: All
Dest Ports: 25
Stateful: Enabled
Source IP: 192.168.0.1
Dest IP: Any

but the Inbound SMTP-ST exception is working well:

Source: Punblic
Dest: Private
packet type: smtp-st
source ports: All
Dest Ports: 25
Stateful: Enabled
Source IP: Any
Dest IP: 192.168.0.1

only after I unloaded ipflt, e-mails can sent out.

what's the reason?