Ah .. okay I see. Looking at the advanced outbound rule you posted, it seems wrong. As the others stated, you need to put this rule above all others in the AON screen. You also need to change the destination port to blank (any). Your server is going to be responding to request on high port with a source port of 25. As others have stated, you also need to change the interface to WAN.
I would open it up first and then lock it down so i would do:
NAT Address: SESRICMailServer
NAT Port: blank (any)
If that works, then just change SPort to 25 if you only want to NAT smtp.