Spam has largely been a solved problem for decades IME. You don't need some big-data-crunching mega-mail-host to block it successfully. For my personal mail, I use a small provider that isn't configured to block anything automatically and the built-in tools in my mail software. For my businesses, we have a pretty standard SpamAssassin-style setup. Either way, I see hardly any spam in my inbox despite receiving mail to multiple published contact addresses for those businesses, and I also can't remember the last time a false positive resulted in missing a legitimate mail.
Meanwhile I've seen people miss events because $BIG_MAIL_PROVIDER decided the invitation was spam, I've seen recruitment go wrong because a CV from an excellent candidate was blocked on its way to the designated email address for applications, and countless other examples where bad spam blocking was throwing baby out with bathwater.
You must be living in a different world than me. I regularly get spam even from large corporations, that I know I never signed up for anything for. I know it is actually them, because it's DKIM signed with their domain certificates. Walmart (which doesn't exist in my country), Unilever and tons or their brands.
Even a national division of Microsoft got hands on my email and decided to sign me up for invites to developer events (I know I hadn't signed up for it, because they didn't even use my name in the mails, which they certainly would have known if they had gotten it through any legitimate source).
I assume it's bullshit KPIs, or signup schemes. Some poor seller at Microsoft or Walmart who's ranked according to how many people sign up to the opt-out company promotions, and buys harvested addresses to juice their numbers.
I even got some very obvious fraud spam ("Your [expensive product] is waiting for you!", trying to get you to sign up as a "product tester" only paying $$$ per month) with full DKIM signatures from a site hosted at a Danish hosting provider, and Danish business info. You'd think this sort of thing gets shut down quickly, but nope. The only times I've tried to address this sort of thing through the proper channels (domain registrar's abuse accounts, etc.), I've only gotten markedly more spam.
At least DKIM signatures makes it easy to autodelete mail. No need to even go into the spam folder, I'm happy to forbid Walmart from communicating with me by mail forever.
Apparently we do live in different worlds. May I ask what sort of email infrastructure you use? I don't think anything I use, either personally or professionally, is particularly complicated or unusual but apparently our recent experiences have been very different.
Probably 95% of the spam I receive is automatically filtered to a spam folder, with a negligible false positive rate. Every now and then some new pattern does make it through but once I've flagged a few instances the rest start getting classified as spam automatically.
I have a gmail account and a RoundCube thing at my own domain (managed by the domain name provider).
Gmail's spam filtering is very generous to DKIM-signed mail - it has a tendency to let it trough even if I've flagged exactly that sender before (as I did with walmart). The one on my own domain has received too little spam to tell how good the filter is.
Sure for you, but all of these other mailservers still obviously find value in applying spam filters or they wouldn't keep filtering.
The problem is that it's much easier to send email than it is to receive it. This puts the onus of spam filtering on the recipient. I'm sad that HashCash or some other PoW scheme was never adopted as a way to force rate limiting of mailers.
Sure for you, but all of these other mailservers still obviously find value in applying spam filters or they wouldn't keep filtering.
But since they have no accountability, their incentive is to eliminate anything potentially hostile regardless of the collateral damage from false positives. What are their users going to do? Take their business to another big provider that will probably be doing the same, and in the process lose access to a bunch of online services they like because their accounts on those services are tied to the old address? Move to a small provider, which is being forced out of the network by the giants so can't deliver mail reliably?
We are rapidly heading for a world where email is no longer a reliable communications medium for genuine messages between friends, family, work colleagues, etc. The giants are killing email through death by 1,000 cuts instead of a shotgun to the face but the end result is the same.
Meanwhile I've seen people miss events because $BIG_MAIL_PROVIDER decided the invitation was spam, I've seen recruitment go wrong because a CV from an excellent candidate was blocked on its way to the designated email address for applications, and countless other examples where bad spam blocking was throwing baby out with bathwater.