I think this new feature – whitelisting subjects – is going to be extremely powerful to avoid false positives. There are a lot of words that spammers would never use in the subjects of their emails that are related to your specific business. Suppose you are an auto repair shop. You might white list phrases like:

• brakes
• alignment
• wheels
• oil change
• paint job
• appointment
• drop off

Unless the spammer is targeting your industry they would never use these words and customers who do use these words would always get through. All you have to do is go through the subject lines of your common emails and look for words that are used a lot but never used in spam.