My personal mail server kept getting IP blacklisted, but only on Microsoft Outlook. I kept submitting it as non spam, they kept accepting and then couple days l

My personal mail server kept getting IP blacklisted, but only on Microsoft Outlook. I kept submitting it as non spam, they kept accepting and then couple days later it was back on. No mail relay, no unwanted traffic, nothing. They seem to have some weird way of blacklisting whole IP ranges. In the end what helped was moving the machines at hetzner to more expensive ones, which put them in different IP ranges. Even before the age of Mailgun I remember outlook being a problem at a startup I worked at. There's also dnswl, but dnswl doesn't help for low volume senders.