I've been a loyal DigitalOcean customer for five years and recently all my email servers are being put on to blocklists constantly (UCEPROTECTL3/UCEPROTECTL2 being the most troubling ones). I decided to try and have a conversation with one of the blocklists and their view is that DigitalOcean allows large amounts of spam to be sent from all its IP address ranges and not doing enough about it.
AWS and Azure apparently do not suffer this problem as strongly as DigitalOcean, and right now I'm forced to consider moving some of my servers to either of them. AWS, for example, block port 25 by default and you must request it be unblocked and you're told your traffic will be monitored. I'd be more than happy if DigitalOcean did the same to keep spammers off of the service.