The new Yahoo Mail is now the one and only version available to users. Up until this week, the 16-year-old Yahoo Mail Classic and the more modern but still old "new" Yahoo Mail were still available, alongside the latest Marissa Mayer-edition Yahoo Mail.
However, Yahoo is upgrading everyone to the new Mail, whether they like it or now. At least, Yahoo is also rolling out a few new features and updates of the new Mail, to soften the blow perhaps.
For one, the new Yahoo Mail now has infinite scrolling. If you want to find a particular message from a few days ago and don't want to search for it, you can now simply scroll down in the inbox until you hit it.
With infinite scrolling, there are no longer pages in your inbox. Press the arrow button if you need to go back.
At the same time, Yahoo has also made it possible to move the preview pane to the right rather than at the bottom. That's if you use the preview pane, of course; you can press “v” to toggle it on and off.