Sounds more like using outlook.com is a mistake. I've been running my own mail server for over 20 years and outlook.com is literally the only domain I have had problems with, and this is the only reason that I now send via Scaleway's free transactional email service.

The people working on outlook.com are just talentless amateurs - the rest knows how to do it right. It's a shame it's so widely used.

I don't disagree, but what are your options when a giant portion of the population uses O365 and outlook.com? How are you going to get them to stop using it, so that legit emails from user-owned servers are not silently rejected?

Most of them wouldn't even care probably...