I've just sent out the second muse-letter which you can view online or, if you haven't already, join me.
It looks as though my host is having issues sending to hotmail or outlook.com addresses so I'll need to check what's going on but I think it's getting blocked because the IP address of the mail server has been flagged.
That's the problem with shared hosting where everyone's accounts are following the same routing. It only takes a couple of bad actors to ruin it for the rest.