I self-host on Linode, and they occasionally fall into UCEPROTECT level 3 (the ISP-wide blocklist), likely due to a spammer trying to set up business as a Linode client. You can't really do much about ISP-wide blocklists, and honestly mail servers should not aggressively reject E-mail simply because some other rando at the ISP sends spam. I've always had success working with the aggressive mail server admin to get unblocked. Often it's just an E-mail to provider-abuse@provider.com
They come across as pretty scummy: "Yea, we put your whole VPS provider in our blocklist. It's their fault for having one spammer customer: Blame them! By the way there's nothing you can do about it--except of course pay us to be whitelisted..."