I have fastmail configured to accept *@{my name}.{my domain} and then I have a rule for each blocked sender. So it's it opposite of the logic that you want: I'll receive they mail until I explicitly block you.
This is still not implicit block like you're after, but when I looked through the settings to see how I had it configured I discovered this integration with 1password: https://1password.com/fastmail/
At least from the promo video that seems very much like Apple's "supply a unique email" feature. Which is better than nothing, but waaaaay less feature-ful and much more manual than my ideal setup.
This is still not implicit block like you're after, but when I looked through the settings to see how I had it configured I discovered this integration with 1password: https://1password.com/fastmail/
which, now that I know about, I may start using.