I have a Nokia Lumia 1020. It just stopped syncing my Yahoo email to my Yahoo app on the phone. It keeps asking for my password and telling me it's incorrect.
- On your phone go to Settings → Email and accounts. Find Yahoo email, press select option to delete.
- On a PC open a browser and go to Yahoo email. Click on your account name and select "Account settings". Go to "Security of account" and scroll down to where says "Allow apps with less security". Enable this and log out from your email.
- On your phone again go to Settings → Email and accounts. Add your Yahoo account, enter your email and password and sync to finish.
IMPORTANT: when on PC or on the phone or app you get a message about device with less security, select "I understand the danger".
Recently revived an old Windows Phone and the process has changed since the last answer.
Now, prior to setting up the email account on the phone, you need to
- Login to Yahoo account on another device (I used a desktop computer)
- Go to Settings -> Account Security -> Manage app passwords (had to scroll to the bottom to see it)
- From here, you click on the "Select your app" drop down menu, choose "Other App"
- Give it a name (ie like "Windows Phone", it doesn't really matter what you call it), then click Generate
- It displays a 16 character string. Go back to your Windows Phone and setup the Yahoo account again, except this time, instead of using your usual password to create the account, use this 16 character string instead. Note that you do NOT enter spaces, just input the characters themselves