Route Email Domain to Specific SMTP Host

Hello Members, I would like to know how to configure the FortiMail appliance to route outbound emails with a specific domain suffix to a specific external SMTP server. The domain is not published and does not have an MX record, only an IP address. The SMTP server is open and unencrypted on port 25. It will accept emails from a client when sending directly to the IP. However the FortiMail appliance will not route an email as it does not know the domain. In Microsoft Exchange it is straight forward as it requires a " Smarthost" configured on a send connector. I have no idea how to configure the same smarthost on a FortiMail appliance. Any guidance is greatly appreciated. Thanks all. -Tom-