For instance, I am self-hosted and I don't pay for DNS since now, most registrars are gated by whatng cartel web engines.

Then, I have an email address with an IP literal (mailbox@[x.x.x.x] and mailbox@[ipv6:...]), this is stronger than SPF since the second the SMTP server IP does not match the IP literals from the email address, in the envelope and the headers, the email is dropped (not event spam).

Currently, the "geniuses" at gogol ask for a DNS PTR record when I tried to send an email to somebody on gmail. My ISP does provide a reverse DNS service... gated by whatng cartel web engines unfortunately.

All this is so much convenient: destruction of all small alternatives... yeah... how convenient...

Until govs and regulators understand they have to go technical to calm down those corporations, things will get worse and we will end up with compuserv and AOS all over again.