Unsub from Forum mails

Switch to the user's account, hover on the profile picture of the user on the top right of the screen, click the "forums" then click "Subscribed Topics". That page list down all the forums and forum topics the user was subscribed to. 

If they're not subscribed to a topic but still get emails, check if they're subscribed to the ENTIRE forum.

To unsubscribe on the forum, under the "Subscribed Forums" section, click the link/s of the forums and it will be redirected to the page that contains the "UNSUBSCRIBED" button.

To unsubscribe on the forum topic, under "Subscribed Topics" section, click the "x" button of the each topics.