LibAnswers does a good job of isolating spam from the LibAnswers Dashboard. You can view the spam at Dashboard > Spam.
Sometimes spam does get through, but you can help to move these emails to the appropriate spam folder. To mark as spam, select the no symbol below the ticket ID. This places it in the spam folder, where each email is deleted after 30 days unless previously manually deleted. Emails must be unanswered to mark as spam.