I’m not NAT’ing through the firewall. I’m using the firewall as my relay host. This firewall has a email protection functionality, so I want to have it scan all the email receiving and sending. So the incomming mail will be delivered to the firewall first, this will than be processed and, if OK, sent to Mail-in-a-box. Than what I want is when I sent a Mail, It should be sent from Mail-in-a-box to the firewall and that will than forward it to the destination. Can that last part be done with the link you sent?