The easiest way of dealing with spam is to use the Ignore function as seen in the screenshot below. Ignore will close the ticket without sending any outgoing email templates. It will also remove it from any built-in reports so it does not affect statistics. You can however create a report or modify them if you do want to show ignored tickets.
Aside from ignoring it is a good idea to create ignore filters to prevent these emails from being imported in the first place. You can do so by navigating to Configuration\E-mail Settings.