The big email players are accepting mail from universities and large companies with misconfigured email servers. If you use the same rules that Google and Microsoft use to refuse emails, you will be bouncing emails from valid domains. If you don't apply them, you end up accepting spam. The big players are able to deal with the spam using specialised teams and I suspect advanced algos including machine learning.
IF the big players applied their famous rules to everybody equally, everybody, including universities, big companies etc... Would quickly configure thier mail servers properly, which WOULD reduce spam, possibly eliminate it.
Being able to keep inboxes fairly free of spam in a world full of spammers is what distinguis big email providers and enable them to sell their services.
I remember when I imagined big companies might use their considerable resources to put together something like that. Then I found out it's just a handful of random engineers cobbling together crap and hiding it behind a fancy domain name.
It is probable that Office365's entire spam filtering system is a very large and ugly spreadsheet that gets passed around between a few teams using a ticketing system.
Relevant wikipedia page: https://en.wikipedia.org/wiki/Exchange_Online_Protection
Originally, the product started out as an acquisition, and there's still some legacy code that references the old Forefront name. There's about 50 people on the team.
DKIM/DMARC/ARC is worked on by two engineers.
Right now, Google is refusing to deliver email from logwatch - giving me the "Message rejected. See https://support.google.com/mail/answer/69585 for more information." so those are going to /dev/null with no recourse to fix it because Google literally doesn't like the content of the email.
The fact that I can't hit a button and tell Google that yes indeed I'm not trying to spam myself is ridiculous.
That said, my outcoming mail traffic is almost non-existent outside of few test emails, LoL.
After setting gmail to forward everything, I noticed it was sending 33% of my legitimate email to spam.
They don’t let you disable the spam filter, but you can set up an escoteric filter that prevents it from actually putting stuff in spam.
I honestly don’t understand how people cope with gmail. Fastmail is cheap and orders of magnitude better.
I like the idea of hosting my own email but even if I get around to doing that I will still need a backup. Fastmail is probably where I will go.
It's harder to sign up for a Gmail account than it is to register a domain and get some hosting. And Google has their own protections against sending large amounts of mail built-in. The system is as it is now because spammers will abuse it otherwise.