How can I mass delete old emails from my icloud inbox?

Either in the Mail application on your Mac, or on the iCloud website: click the top message of those you want to delete, then shift click the bottom message to select everything between them. On your Mac, hit the delete key. In iCloud this may work, or click the dustbin icon.

Then in Mail hit shift-command-delete to empty the Trash (all accounts) or on the iCloud website click on the cogwheel icon at top right and choose 'Emtpy Trash'. This last is not undoable.

Finally!! I can empty my inbox of all unwanted emails lol, Thank you!!