Issues like - Yahoo mail not working, Yahoo mail service down, Yahoo mail crash, Yahoo server status, etc. can disappoint users. However people can troubleshoot all these errors by applying the correct methods. To fix the Yahoo Mail problem, first you need to check whether your Yahoo Mail status is down or alive. If your yahoo mail is not down, then you can check your phone settings properly, because sometimes yahoo mail does not work due to some small things like - slow internet issue, wrong password, cache and data etc. So you need to fix all these things then you can resolve your problem.
See also - http://www.onlinegeeks.viamagus.com/blog/Is-Yahoo-s-Website-Down-Right-Now.html