"Blacklisted" probably doesn't have a sufficiently clear definition. I don't even run my own server, just use a custom family domain that is served by protonmail, and discovered when trying to go through foster licensing that virtually all of the agencies were not reading my e-mails because Microsoft and Google alike were routing them into the spam folder, but they weren't being blocked or bounced. I wouldn't have even known if I hadn't called a few and asked them to check.

I am definitely not being flagged for any actual spam-like behavior. I might send out 40 e-mails a year, and even though it's a "family" domain, I'm the only one who has ever used it, ironically enough, as part of my decade-old effort to de-Google.