Earlier quoted context omitted.
Ah, I don't really care about telemetry, but their amazing outlook.com SMTP service rejects mail from small senders, and there's no way to successfully appeal. Yeey, brave new megacorp world!
What’s the difference between a small sender and a spam host?
Before I moved to fastmail, my email was consistently getting nullrouted by microsoft. Everything was setup correctly (SPF, DKIM, DMARC, ARC, etc...), and every other mail host I tried would receive my mail correctly. I send out a very low amount of email (3-4 per month?).