I heard from a friend internal YMail would have ads too because the YMail team needed to test the ad product of YMail... which is kind of ... eh.
I had to communicate with sales constantly (worked on the front-page ads team), so email was essential, unfortunately.
What kind of work did you do that didn’t require email?
I left in 2016 and in practice we just didn't use email at all because it was so painful to use.