That's just one current example of when email delivery matters, likely to resonate with HN as being senders and receivers they recognize struggling with this. Not just a Microsoft thing, we can talk about a dozen where Gmail files things wrongly as well, and where the common element is the mailer.
These mailers all have different levels of trust and deliverability stats. It's critical to know.
I don't think you're getting what I'm saying here. If an email provider is throwing away wanted messages from legitimate senders because of some "trust" metric, then it is that email provider's reponsibility, not the sender's, to make damned sure that doesn't cause the loss of desired email.
You are of course correct that neither GMail nor Microsoft 365 or Hotmail or whatever they call it this week is suitable for any serious use.
You don’t have deny the responsibility of the relevant authorities to properly maintain hiking trails, in order to place responsibility on a hiking guide to safely get you along poorly maintained trails.
These mailers all have different levels of trust and deliverability stats. It's critical to know.