Hi Pwizard,
some question:
what kind of ip addres you have configurate in you SMTP Home?
not a domanin, true?
if you have setting the ip pubblic of the macchine, you must to make a rule for trasfert the request from the RED zone to DMZ Zone where there is the mail server.
read this post for know how
http://efwsupport.com/index.php?topic=156.0 .... when you set the port, you must only use the port 25.
bye