Some servers blacklist you no matter what you do because you’re not a big player in the e-mail space… Outlook. Fuck Outlook. M365 doesn’t do that though.
Also the idea that reverse IPs are needed (in practice) when SPF, DKIM and DMARC are in use is insane. I have literally told you my public key and signed the e-mail. It’s me. You don’t need to check the damn PTR!