How do MBPs test new spam filters before rollout?

MBPs test new spam filters through gradual rollouts and A/B testing on small traffic samples before full deployment. They might apply a new filter to 1% of incoming mail, measure false positive rates and user feedback, then expand if results look good.

Shadow testing is common: the new filter runs alongside existing filters, making decisions that get logged but not enforced. Engineers compare outcomes to identify cases where the new filter would have blocked legitimate mail or missed spam that existing filters caught.

User feedback loops accelerate this process. When users mark messages as spam or rescue messages from spam folders, these signals help validate whether filter changes improve or harm the user experience. Only after extensive testing do MBPs roll changes out broadly, though even then they monitor for unexpected impacts.