Recently, I managed to get my personal mail server working and delivering to Outlook.

Of all the major mail providers, I found getting my mails to Outlook the hardest. Gmail played nice once I setup DKIM, DMARC, SPF, MTA-STS, rDNS and a couple more things that I forgot setup exactly the way they like it.

Outlook was harder though. I had to send a series of mails spread over multiple days to people who had Outlook accounts and get them to both mark it as not spam and reply to the mail until it eventually started working.

It's been a couple of months, not sure if it still works though. Hope it does.