Is this new?
I have a small mail server running on a Linode VPS. It was up and down as to whether emails got delivered. Google, Microsoft and Apple were the most likely to refuse delivery. I traced the block to UCEPROTECTL3. I looked into their policy, as all the other blacklist sites were fine. Turned out that although MY IP address was clean, as were all other in the subnet, I still get marked as spam because I'm with Linode. They are asking for £20pm to whitelist my IP. Sounds like a protection racket to me. Thankfully, the server is so low volume I can use a reputable mail forwarder for next to nothing.