How to Delete a Yahoo! Mail Folder
Yahoo Mail won’t let you delete folders that aren’t empty, so you must first delete or move any emails out of the folder.
To remove a custom folder from Yahoo! Mail:
Open the folder you want to delete. Click the Select All box at the top of the inbox to highlight every message in the folder. Go to the main toolbar and select Delete, Move, or Archive to empty the folder. Set up your Yahoo! Mail account via IMAP in an email program to quickly move or archive messages. When the folder is empty, select the dropdown arrow next to the folder name. Choose Delete folder.
Delete Folders Using Yahoo! Mail IMAP
You can also delete folders using Yahoo! Mail IMAP and have them removed from Yahoo! Mail on the web as well as in other email programs connected to the account via IMAP.
To delete folders using Yahoo! Mail IMAP:
Right-click the folder you want to delete. Select Delete from the menu.
Delete a Folder in Yahoo! Mail Basic
To delete a custom folder from your Yahoo! Mail account using Yahoo! Mail Basic:
Open the folder you want to delete in Yahoo! Mail Basic. Move any messages you want to keep. In the folder list, select Edit next to My Folders. Under My Folders, select Delete next to the folder you want to remove. In Yahoo! Mail Basic, you don’t have to empty the folder before you delete it. Messages in the folder are moved to the Trash folder. You can recover them later. Under Delete Folder, select OK.