Cheating

My husband has emails in his spam folder from dating websites. I understand that if he had a profile in the past because he uses the same email address that that is where thoes would come from....but what about craigslist casual encounters? If he was using the same old email address could he occasionally still receive these or has he been using the site? Or is it from porn sites. I am uneducated and feeling like I need to check into this. Is he cheating on me with women online?