Spam senders who use their own infrastructure is pretty much solvable using things like reputation score. Details varies but they generally work good enough. He

Spam senders who use their own infrastructure is pretty much solvable using things like reputation score. Details varies but they generally work good enough. Hence, most spam piggybacks on other infrastructure. At the time of IM2000, an eternity in Internet time, most of this was done using open or poorly secured relays. Reputation score worked well for that too and that spam vector is closed now. Remaining vectors are hacked infrastructure and the large cloud and free email providers. Storage cost could be relevant to escalate the problem for the latter.