I’ve actually blocked any incoming email without a valid email address (belonging to my domain) in the To: or CC: headers; it’s helped me cut spam significantly.
Using a specific prefix I can generate a new email address for each website I visit. So when someone emails me, they’re forced to tell on themselves and/or the website they stole/bought my email address from.
All this makes it easy to see who lied and sold my shit (data) after I explicitly said not to. And I figure if I really needed to be BCC’d on something, the sender can simply forward the email to me after they receive the rejection message.
I’ve tried them but they never really clicked for me. In case I need to block one I add it to a server-side Sieve filter.