Google's policies get exported. For a long time it was OK to drop email that came from a server without rDNS. Then gmail started allowing such emails, and then

Google's policies get exported. For a long time it was OK to drop email that came from a server without rDNS. Then gmail started allowing such emails, and then legit sites started sending email from servers without rDNS. In this case the export mechanism is Captcha v3.