They’re using the bbPress plugin here on this site, so the way to Subscribe and Unsubscribe are the same on all of the other WordPress sites that use this plugin.
There’s a good chance you may have subscribed to those forums a long time ago. Here’s how to Unsub. Go to the Theme page you want to unsub from (let’s use Ambition for example) https://appfinite.com/forum/ambition/
Then look for the Breadcrumbs section (right under the title)
Home › Community Forums › Ambition Unsubscribe
Click Unsubscribe
I believe that should work for that entire Theme Forum. You may have to do that for each Theme you’re subscribed to.
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However, if you create a new thread in a forum, or if you reply inside of someone’s thread, then anytime there is a response in that thread you’ll receive an email. That’s pretty normal, but I think you can still unsubscribe from those threads individually by clicking the Unsubscribe link near the top of where the thread begins.