email is turning into a walled-garden of big tech.

For instance, I am self-hosted, that without DNS. The email designers were carefull to make the email system work without DNS, that with email addresses with IP literals: mailbox@[x.x.x.x] and mailbox@[ipv6:...] (and I guess once ipv4 is really gone, the ipv6: prefix will be dropped).

This is stronger thas SPF, since as soon as a IP literals in the envelope and the various "from" headers does not match the actually IP from the sending SMTP server, the email is dropped, not even going in spam.

If I send such email to gmail for instance... I get a 'missing a DNS PTR' record, go to hell. How, convenient, to send an email there, you must have bought a DNS domain, knowing perfectly that most registrars nowadays are gated by the web engines of the whatng cartel... which gogol, then gmail does belong to... how convenient, the crime is almost perfect, I don't put that on the account of incompetence, this is beyond that, we are in the realm of toxic malice.

I do presume now they know what they are doing, killing all small tech, or self-hosting is in their agenda of dominant internet corporation.

I think it's more they simply don't register small tech and self-hosting.

In time there will be a reckoning though. The geopolitical instability at the moment will see the end of the US dominant services used outside of the US so they will have to work out how to make a not small but balkanised email provider model work again.