I was having trouble with my Yahoo! too. I did a hard factory reset. After the main set-up, I tried to add my Yahoo! mail. I got a Cannot connect to server and another error : 503 10102 LDAP lookup failed. It won't allow me to add the email, when in fact i was working up until the reset.

 

I got my email working by going to settings, select emai from "accounts". Select "settings" under common settings. Select your account under "added accounts" and remove the "@" and anything that follows. Save it and try logging in. You may need to reboot your phone.
Also make sure your logged into your account via your yahoo, gmail or other account.
Let me know if this works. IT WORKED FOR ME.
terofpa

 

I got my email working by going to settings, select emai from "accounts". Select "settings" under common settings. Select your account under "added accounts" and remove the "@" and anything that follows. Save it and try logging in. You may need to reboot your phone.Also make sure your logged into your account via your yahoo, gmail or other account.
Let me know if this works. IT WORKED FOR ME.
Terofpa