i mean that's a rather large group of people you can't communicate with right there.
and it's the only one you know about.
i say this is the exact reason running your own mail server in 2018 is problematic. you just chose to not consider it a problem.
It's a reason why allowing these fairly core services to be provided by a shrinking group of organisations is equally problematic.
Maybe one day Google will decide that they get too much spam from outlook.com (or vice versa) and cut them off too. What are you going to do about it, set up your own mail server? Vote with your feet to another provider? Start a company doing the same? Good luck with that.
>.. it's the only one you know about.
In the case of outlook.com, there's a delivery failure message. My yardstick is gmail.com. If the mail is getting to gmail accounts then I'm confident that it's as good as it is going to get.