The method is quite simple and it takes no time at all to get the old version back
Yahoo’s new mail is annoying a lot of people. Part of this is because people don’t really like it when changes this big happen overnight, while another part can be blamed on all the bugs that have been reported over the past week.For everyone that wants to find a way to get the old Yahoo mail back for a while, there’s a really easy trick for doing so.
Once you are logged into your account, the URL ends in “mail.yahoo.com/neo/launch?.rand” right between a series of numbers that vary between users and login sessions.
In order to get the old Yahoo Mail back, you simply have to go to the URL bar and replace “launch” with “search”. Thus, the URL should now look as follows “mail.yahoo.com/neo/search?.rand” (obviously still surrounded by various other numbers).
Once this is done, you’ll find yourself on the “Search” tab and can quickly go to the “Inbox” tab in order to view all messages.
Yahoo Mail works as it used to, with mails opening up in different tabs, the folders are visible to the side and so on.
(Thanks to user Naldydee for the tip!)
[Update - October 23, 2013] Here's how to get a more permanent solution when switching back to old Yahoo Mail.
[Update - November 11, 2013] Since this workaround no longer works, here's another way to get your old Yahoo Mail back.