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- S/O ratio of 0.95 or greater (or 0.05 or less for nice rules)
- > 0.25% of target type hit (e.g. spam for non-nice rules)
- < 1.00% of non-target type hit (e.g. ham for non-nice rules)
- not too slow
- TODO: criteria for overlap with existing rules?
A ruleset in the "extra" set would have different criteria.
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