I have a shiny mail server on gioorgi.com. I decided to manage it on first person because it is important.
I had some troubles sending mail to Hotmail: they banned my IP. So I find out this fantastic site which will check for you a tons of things, like correct DKIM signature and so on.
So I was able to open a ticket to Microsoft exposing the issue. And it is incredible, a real guy answered (or a super AI-azure powered robot running on WindowsServer…I dunno but I think it the guy is cheaper).
Microsoft solved the issue in a week, smooth like a glass.
Extra tip: refer to https://www.rackaid.com/blog/hotmail-blacklist-removal/ too for a list of tips