I wonder if their recent domain change from tutanota.com to tuta.com has anything to do with it. I remember many users didn’t like how they did it because only paid users could claim their new tuta.com email, meaning if you are a free user, someone else can sign up with (your-email)@tuta.com essentially making their email look more legit than your tutanota.com email. For reference, protonmail gave all users an equivalent proton.me address for free. Obviously MS needs to rectify the situation, but it would be interesting to know if the domain change is related.