Oh, that's a great idea. Currently, every user has their own private list (it's just text files). It takes a bit of work initially, as you need to approve each email, but it's totally worth it. And it must be per user IMO, as your friends and family have different emails, so its less about public or legit domain, but more what domain and e-mail YOU trust.

But great idea, what i added is the opposite direcrection: showing if a sender used spy pixel. There I used public spylists I found.