>...and everything you mention doesn't help shit for mitigation of spam because all spamming domains have SPF entries meanwhile, too.
It does help stop false attribution of spam mail, though; spammer@example.net can't pretend to be sending mail from example.org.
It does lose its effectiveness when huge mail domains (e.g. GMail) can pump out so much spam, though, or when domains share email hosts (and therefore different tenants will be sending from the same IP addresses - another reason why IPv4 exhaustion is bad, isolation would work better with IPv6).
It does help stop false attribution of spam mail, though; spammer@example.net can't pretend to be sending mail from example.org.
It does lose its effectiveness when huge mail domains (e.g. GMail) can pump out so much spam, though, or when domains share email hosts (and therefore different tenants will be sending from the same IP addresses - another reason why IPv4 exhaustion is bad, isolation would work better with IPv6).