[DNied]

So far, only Microsoft has been a nuisance to my personal SMTP server (there's an open issue about Microsoft's dubious blacklists on GitHub, with several participants: https://github.com/MicrosoftDocs/microsoft-365-docs/issues/5...).

Just a little part of why I hate and mistrust that company.

[BenjiWiebe]

Me too. I've repeatedly had deliverability problems to Microsoft. Everywhere else has had no problems apart from the initial setup when I didn't know what I was doing.