Yahoo keeps 80% of all emails from being sent, because they suspect it’s spam. That doesn’t mean the remaining 20% isn’t spam.
in my experience, Yahoo is terrible at catching spam. Maybe half of it is caught, with some legitimate email marked as spam too.
It's interesting how different peoples experiences of that are. I have an "ancient" Yahoo Mail address that I don't use much but that receive a massive amount of Spam, and pretty much nothing gets through.
I do not believe Yahoo Mail's assertion here. I have a Y! Mail account (which I do check once a week) and almost 80% of mails are spam. So they are not doing a good job at it (vs. GMail which is the other email provider I use) and thus their metrics here look skewed to me.