[walrus01]

It's incredibly entitled of some big cloud based operator to send mail from an SMTP source that doesn't have proper reverse DNS. Any normal independent small operator sending mail without proper reverse DNS will increase its likelihood of spam rank by a thousand percent. Or get flat out rejected at the SMTP negotiation process or relay attempt.

But things like icloud, office365, google workspace and similar are "too big to fail", right? They don't have to play by the same rules as the rest of us peons.

as referenced here, from the post on the 'mailop' mailing list

https://news.ycombinator.com/item?id=43512353

This is either an astonishing level of technical fuck-up from what has to be an entire work group of people with six figure salaries whose jobs are nothing but running email server infrastructure, so they must clearly know better, or a lack of regard for the internet community and accepted standards. I really cannot think of a third possible explanation for it.

To be clear for those people who don't run their own email servers: Having proper reverse DNS for the IP of your outbound SMTP sending server is one of the absolute bare minimum requirements for accepted mail flow, and is a standard that's probably 25 years old or older now. It significantly pre-dates SPF, DKIM, DMARC and all the rest. Proper RDNS is literally one of the first things you verify before you set up everything else.