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)

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