Why does MailScanner marks some as spam even when custom function changes score to way below spam threshold

[Rick Duval]

I have a custom module on Mailscanner that often will add(subtract)
100 points so the finished score is (for instance) -160 but sometimes
the emals still get marked as spam.  Anybody know why or how I can
stop this?

Also, anybody know how to set the "whitelist" or "blacklist" flag in a
custom plugin module?

Thanks