Tell me you've never run a mail server without telling me you've never run a mail server. It's pretty standard practice for there to be a gradient of anti-spam

Tell me you've never run a mail server without telling me you've never run a mail server. It's pretty standard practice for there to be a gradient of anti-spam enforcement. The messages the scoring engine thinks are certainly spam don't reach end users. If the scoring engine thinks it's not spam, it gets through. The middle range is what ends up in spam folders.