I'm deeply sorry, that you have to read those disgusting words in your mailbox. To be honest, it even hurts me.
There are tons of people like this, I observe this behavior more and more these days. Go and talk to a random youtuber/twitch streamer how much hate they have to deal with for their "free" content.
I once thought its the German culture (doing business and earning money is almost a nono-thing in Germany and makes you an easy target), but I guess some humans are just like that...