SendGrid owned by Twilio did it to me in 2023 and here we are making peer to peer email service.

Also textplus.com did it to me and I lost my phone number after several years of using it saying I violated that terms of conditions without doing anything.

www ?

Some providers use the reputation of the mail servers (smtp.domain.com) and not the actually domain (your-domain.com).

I beg to differ on:

> but if your home internet checks these boxes, you can 100% host your own mailserver at home:

    Static IPv4 address (make sure it's not blacklisted)
    Not behind a CGNAT
    Ability to change the PTR record of your IP (usually though the support of your ISP)
    Ability to open common mailserver Ports (25,143,465,587,993)

Because above is only needed if you want to communicate with people using Gmail, Yahoo, Outlook, Fastmail, Proton etc (The monopoly).

For normal folks, they are better off using an alternate less privileged email service like email.riamu.io.

email.riamu.io comes to mind

How is it different from an agent using SMTP to use existing email made by human? Using something like https://email.riamu.io

EMAIL - email.riamu.io