When you can't access the yahoo mail account on the phone or computer. it means, something is wrong with the user account or password. here are the guide to fix the problem.
1. First of all, you need to check the username and password.
2. Update the server status. make sure that the server is working fine.
3. Check the incoming and outgoing server status. make sure that the servers are working perfectly fine.
4. Let's remove the current account from the mail application. now re-add the mail application on your smartphone.
once you will make these changes into the yahoo mail account. it will start working fine. for more details, you need to visit down reporter blogs.