Speaking from personal experience working with these reputation warehouses and with handling a good deal of incoming and outgoing email volume, they aren't any more effective than other IP-based spam heuristics and if everyone configured their DKIM correctly these warehouses would be largely obsolete. I don't see a problem with crowdsourcing heuristic data per se, but email is a much narrower field than internet traffic at large and I can see a lot of the ways that poorly configured fail2ban type software could accidentally ban a lot of valid traffic.
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