Advertising has been increased on the forums webpage, unfortunately (you can send feedback to Mobile Nations to let them know you noticed and it's excessive... I have, and even Phil N. from the AC Blog did, they're looking into it).
As for the e-mail, however, that is definitely not from AC. While the AC Forums app does rely on Tapatalk, it doesn't send spam e-mails to your account. But that doesn't mean that if you signed up for Tapatalk or something like that before, your browser cookies and history won't 'reveal' that you use AC a lot and uses that to suggest app usage to you.