gmail, outlook and salesforce create about 90% of the spam that gets through blacklists. Salesforce is simple to fix: I just block anything from salesforce from our network, as it just seems to be 100% used by spammers. Gmail and outlook are the major problem, as there is no way of addressing their spam issue.
In my experience, everyone got their act together except Google. I also used to receive massive amounts of spam from Azure and Sendgrid but this eventually stopped. Now 80% of the spam I receive is from the Google network, mainly Google Cloud.
Add Mailchimp in there as well. I have never gotten an email from someone using Mailchimp that was not spam.
Yeah, Salesforce clearly has some kind of whitelisting at Gmail. I get so much nonsense from that domain.