Hello Chris,
So generally for our products we keep the scoring of messages confidential. The reason for this is that we don't want spammers "reverse engineering" the scoring of the product in a way that would allow them to bypass filtering.
However what I can tell you is that we still base our filtering on a scale. What happens is that we have many different rules that have specific weights. If there is a rule with a 100 weight or if the conglomeration of rules adds to 100+, it will be flagged as spam by Symantec. Anything below that would be scored under "suspected spam" which is configurable by you.
I'm sorry if this doesn't really answer your question, but as you could understand we want to make sure that our customers are protected as best and as long as possible. If you need clarification feel free to ask.
Thanks!
Tom