The article the describes the appliance's functions
Symantec Messaging Gateway
You can use each of appliance to perform a variety of functions. During the initial setup, the installation wizard prompts you to choose the function that each appliance performs. Symantec recommends making decision which function or set of functions should be assigned to your appliance, before installing the product. Contact a sales representative for additional help with performance sizing.
The available functions are as follows: