While Yahoo! Mail may not always (at least not immediately) display all messages in a folder, you can highlight (and then act on) all the emails with one swift click.
Select All Messages in a Yahoo! Mail Folder
To highlight all a folder's messages (for deletion, for example, or to move them) in Yahoo! Mail:
- Make sure you use Yahoo! Mail and not Yahoo! Mail Classic to access your account.
- If you currently use Yahoo! Mail Classic, you can switch temporarily and return to Classic once you've taken the action on an entire folder.
- Open the folder whose messages you want to select.
- Click the checkbox in the message list's header.
Even if Yahoo! Mail does not display all messages, they are all selected and you can now operate on them in one go.