When Outlook and Hotmail reject your mail server: error S3150
A reply from my own mail server to an msn.com address bounced with a block-list code. SPF, DKIM and DMARC were all fine. The block was on my hosting provider's network range, and the practical fix was to send that one mail another way. How to read the bounce, what does not help, and the detour through SES.
