Non spammers send from a consistent pool of IPs and domains that don’t send crap. By contrast, spammers either send high volumes of crap from a small set of IPs and domains, or they spread a single content pattern over a wide diversity of IPs and domains that do not have a good track record.

So long as you can keep track of literally billions of counters in real time, you can effectively combat spammers.

Source: MailChannels CEO