F.L. Whiteley wrote:
blackholing 10,000 spams/month at the user-configurable server pre-filter

If you are getting and ignoring over 3000 emails per _day_ I can't see
that you can know that none of those are legitimate email. I don't know
of any perfect spam filter and the black hole lists are also not perfect
as there are documented cases of innocent IPs being "collateral damage"
of over-zealous listings.