In looking at my Postfix mail.logs, I only see the new ICANN vanity gTLDs really generating garbage spam. Lots of press on the mess this all is causing. I got kind of sick of even dealing with that, so here is the header_checks lines I use to block them via postfix if you want to do that on your setup. There are a lot of articles on the internet for this, but I here is what works for me. YMMV...