How to Permanently Delete Yahoo Mail Messages
You can empty the Trash folder by permanently deleting messages in your Trash folder in the web version of Yahoo Mail.
How to Empty the Trash in Yahoo Mail Basic
To purge all mail from the Trash folder in Yahoo Mail Basic, select Empty next to Trash.
How to Empty the Trash in the Yahoo Mail App
To empty the trash in the mobile app:
How to Recover Mail After You’ve Emptied the Yahoo Mail Trash
If you act quickly, you might be able to recover messages you deleted from your trash folder. Either download all the messages that came through your Yahoo Mail account, or forward them to a different email address either automatically or manually. You’re not technically undeleting so much as you’re racing against time before the Yahoo servers fully synchronize your deletions across all your devices. To recover an important message after it has been purged from the trash: