The interface, blocking spoofed email addresses
Interface Design: I tried the new, and just like each prior time, the interface --for what users prefer-- keeps getting worse. But eventually we adapt, which seems to signal yahoo to change it again. I have been dissatisfied with each "new yahoo" since I began with yahoo many years ago, but this present new one was irritating enough that, if forced to use it, I am considering Proton's paid version. I've never paid for email, but with the combination of yahoo reducing storage, limiting blocked emails when yahoo fails to block spoofed addresses, and these worsening interfaces, I will bear the pain of payment.
4th
ranked