Allowing users to relay through your server
In order to relay through FTGate the users must be Authenticated , either using SMTP authentication or by being from an address that has been granted Automatic Authentication (AA flag) in the appropriate Security Policies.
Thus you have two options:
Enable the users mail client to use SMTP authentication. With this set the default configuration of the Global Security Policy will allow relay.
Enter the users IP address or range into the Global Security Policy and set the PA (Permit Access), AA (Automatic Authentication) , AS (Authenticate by SMTP) and AR (Authenticated Relaying) flags.