I’ve had a different experience. I have been mysteriously appearing in surbl periodically ever since I switched to ProtonMail. Never had that problem in like 10 years of owning my domain, but within a month of ProtonMail sure enough, I started having deliverability issues. I usually get removed fairly quickly but it was still extremely disruptive when important emails would randomly not get delivered. It hasn’t recurred in a year or so, but the situation with no calendar integration is driving me crazy. That’s another topic… I think I am done w Proton though and am going to give in and sell my soul back to the devil.