I think a bounce would be preferable! Why waste someone's time?
I think it should only hell-ban via a special checkmark. By default it should cause a bounce saying that this person is not receiving email from that address. Then neither sender nor recipient have their time wasted going forward.
I mean for the 0.01% of cases where someone would literally create a new address just to continue harrassing you, yeah, you could then hellban their second address.
