The spammers don't attack mail servers, but individual mailboxes.
Your personal gmail account has the same risk of receiving spam as mine, but Google has much more tools available to detect spam. For example they can easily see somebody is spamming, when large gmail accounts are receiving the same message. They can easily see which hosts are compromised proxies as they receive tons of mail, and seeing large number of e-mails sent from questionable hosts should be easy to spot.
They didn't really improve spam detection much for for a decade, because blocking small hobbyist mail servers is more likely increase their user base.
Those special farms you're mentioning, wouldn't work, if filtering would be individual per user, as it should be, because each person's mailbox is different and each person has different definition what spam is.
Your personal gmail account has the same risk of receiving spam as mine, but Google has much more tools available to detect spam. For example they can easily see somebody is spamming, when large gmail accounts are receiving the same message. They can easily see which hosts are compromised proxies as they receive tons of mail, and seeing large number of e-mails sent from questionable hosts should be easy to spot.
They didn't really improve spam detection much for for a decade, because blocking small hobbyist mail servers is more likely increase their user base.
Those special farms you're mentioning, wouldn't work, if filtering would be individual per user, as it should be, because each person's mailbox is different and each person has different definition what spam is.