"I’ve had exactly one problem with deliverabilty during that time, where someone with a Hotmail account complained to never have received my mail - even though the Microsoft server claimed to have accepted it according to my logs. While Microsoft can be notoriously intransparent and unforgiving with (not) accepting mail, in this case it turned out to be a blacklisting issue. I had just moved servers and IP addresses shortly before, with the new IP having been on an internal MS blacklist. I raised a ticket with their mail infrastructure department, and to my surprise, the IP was cleared soon after."

Unfortunately, MS and others have now adopted an "opt-out" blacklisting policy. Even with a clean IP, you'll have these problems if you set up your own server.

(I've been running my own mail servers for 30 years.)