Have you try new Yahoo Mail?
I have a hard time using Yahoo mail before because I cannot find the button to delete all of my inbox in a go. However, once I moved to the new Yahoo mail, all of my messages is sort in one page. Making it easier to download more than 1000 messages in a click.
Furthermore, I feel easier to read mail using the new Yahoo mail because I do not need to change window to read new mail or pressing back button to access another messages.
However, the new Yahoo mail seems to use quite a lot of resource cost I feel a little lagging during access.