How much configuration is required once SecurityGateway is installed?
You will need to configure the email servers that SecurityGateway will be passing messages onto, the method of verification it will use to determine if a local user is valid, along with creating or importing information on your users and email domains. Note that there is a feature to automatically create new users and domains as desired.
Once that information is provided, SecurityGateway should run with a minimal amount of interaction beyond the initial setup.