Oh god let's not get too deep into the "it's actually like" that happens with every analogy used on the internet, haha
Twitch already has adverts and banners, which are closer to what you're comparing to. This would be injecting text ads into the middle of your emails if we're correcting our analogies
E: Unless you mean Google actually does allow companies to pay to bypass spam filters? That's probably something that needs posting to HN itself if so lol