Yes! IMHO every registrar should be turning this on by default. Every DNS should do this by default until the owner explicitly turns on email sending.

It would solve a lot of issues globally.

Also consider (using your example domain):

  *.mydomain.io. TXT "v=spf1 -all"

to restrict SPF on all subdomains.

I use postfix and the recipient_access file to control email to my domains which use little email, so the domains are able to process standard email:

admin@example.com OK postmaster@example.com OK abuse@example.com OK webmaster@example.com OK hostmaster@example.com OK info@example.com OK example.com REJECT example.com