It was flat out impossible for me to get Outlook to accept my mail server. They'd only give me some vague response with no actionable steps to resolve it. I gave up and used a gmail account to route everything outgoing. That way mail still shows up as from:jimm@jimm.horse but rides on Google's reputation. Defeats the purpose a little but there's nothing more I can do (apparently unless I buy my own non residential ISP line, host the server in my house, and build reputatiom forever, but that's an absurd length to have to go through. ideally we'd have antitrust legislation forcing MS et al to be fair towards smaller email and save the open internet overall, but I'm not holding my breath.).