But this is the InfoSec community and your reasons are probably entirely separate.

Infosec broadly covers:

• Confidentiality
• Integrity
• Availability

Your problem as you describe it boils down to availability (which some would say is the most important infosec factor). I also have a serious availability with Microsoft. When I send email to an MS recipient (back in the days when I was willing to), MS’s servers refuse my msg because MS aggressively implements a strict IP reputation policy. And to be clear, you need not ever send any spam to have a bad IP reputation. You can simply subscribe to an ISP that gives you an IP address which the ISP has published as “residential”. And just like that, the discrimination machine kicks in.

MS does not want mail from self-hosters like myself. They want to force me to dance for them. Even though my email is RFC-compliant, MS wants me to subscribe to a more costly business class of internet service, or to pawn myself to another email service provider.

Either way, MS can fuck off. I will not lick MS’s boots.

Out of curiosity, why are you declining to transit Microsoft servers? Worried about inspection or something?

First of all, I boycott MS. The boycott is mostly driven by factors unrelated to infosec. Boycotting is no longer just refusal to buy their junk -- boycotting also means to not feed them data because they profit from the data (otherwise, why are they gratis?) I am not generally worried about info in my payloads being specifically exploited in some kind of attack by MS, but I will not feed MS data that it can profit from. I also protest non-US govs throwing away their digital sovereignty and making all their people lick the boots of a privacy-abusing US surveillance advertiser.