Alex,
If you would take a look at the documentation it states:
"Symantec Messaging Gateway treats mail coming from an address or connection in the Local Good Sender Domains and Local Good Sender IPs groups as legitimate mail. The good sender groups reduce the small risk that messages sent from trusted senders will be treated as spam or filtered in any way. By default messages from these senders are delivered normally. "
To reduce this last bit of risk, as far as i know its the only possibility.
Sorry, but now i dont know what exactly do you need:
- Internet -> one of your users: Mail should get through OR
- One of your users -> Internet: Mail get through?
Why is the need of whitelisting? What exactly is happening, what verdicts, which rule etc.
Depending on that the solution is different
Thomas