Outlook/Hotmail blocks DigitalOcean. After half a dozens attempts over the years to delist my IP, and following all the best practices (dedicated fixed IP, SPF, DKIM, DMARC, FCrDNS, zero spam, TLS, etc.) I gave up. Eventually, most people realize that their Outlook/Hotmail email service is defective because they're not receiving emails, and they migrate to another email service.
This is from DO's own site based on a quick search:
"I am being BOMBARDED, and I mean BOMBARDED with spam from Digital Ocean over 5 spams a day all from the same bunch of domains, all hosted on DigitalOcean and coming from your IPs.
In the last 2 weeks I’ve emailed your abuse mailbox 20+ times and filled in the contact abuse form 10+ times.
NOTHING is being done about it. My next plan of action is to keep posting here until Digital Ocean takes action.
Do you even have an abuse team? are they doing any work at all? I can provide 30 more samples if needed."
Absolutely pathetic - all major providers should blackhole email from DO.
Note that this contrasts to AWS. I was on AWS from flat network days (where folks were running scans internally etc. AWS respond with a ticket usually to abuse reports and then usually a bit later a note that things have been taken care of.
How does AWS which is FAR larger in IP address space than DO have so much LESS spam coming from their IP address space? Perhaps because they pay a tiny bit of attention to the issue.