You're describing SPF and DKIM. Both of which can be used by people sending legitimate mail, and people sending spam... SPF and DKIM are good for preventing so

You're describing SPF and DKIM. Both of which can be used by people sending legitimate mail, and people sending spam... SPF and DKIM are good for preventing some false positives. They're not good for stopping spam. I would bet that currently, well over 90% of spam that is rejected, is rejected because of blacklist lookups.