Google's Strategic Placement of Ads
But, in the process of this little accident, the advertiser lost money, and Google made money. I am not saying this is a scam, but this is a very strategic placement of ads because of these reasons:
1. The ads are relevant to the email I just opened. Which means that by accidentally clicking the ad, I will be taken to a site that is relevant to the email I just read, so it could lead to a possible conversion depending on what the topic is and how much I am interested in it.
2. Since there is very little gap between the "Back to Inbox" link and the "Sponsored Ad", Google gets some free clicks but this is not wrong, in any way, so to speak.
Therefore, due to the closeness of those two links, the chances are that the user may read the title of the ad, and because it is relevant to the topic of the email, it could entice the user to click on those ads.
Using the same concepts in your marketing efforts, you could get some added conversions, or just plain free clicks.