Delete Mails in Mac Mail without Trash
You can delete emails and bypass the trash using

⌥ Option + ⌫ Backspace

(Successfully tested with OS X 10.9 (Mavericks). Could work with older versions, too.)



If you want to delete emails that are already in trash it is enough to hit ⌫ Backspace to delete them permanently. If you are accustomed to also press the ⌘ Command, like deleting a file in Finder, you can do so. But basically, backspace is enough.