I had screened the email test-destroy@yopmail.com in my Discourse instance, and couldn’t register with test-destroy-4@yopmail.com. But removing test-destroy@yopmail.com from the screened emails allowed test-destroy-4@yopmail.com to register.
I’d assume that to be true for the reason that sub-addressing is a thing and ESPs use all sorts of separators e.g. some use + while others use .
So in that sense, if some provider uses - to allow for sub-addressing emails then screening at discourse stands true.
E.g. if someone@example.com is blocked but someone+new@example.com is not then someone@example.com can still register by just adding a +new to their existing email. That defeats the purpose of screening.
So it seems like by design but I’d have a look into the code for an evidence verifying the same.