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Actually it should be called as "Alerts" or something else than "notifications" because this forum isn't a social media.
And there is a button which name "notify" on the top right of every topic to turn on your notification .You should try and see how it works first okay?
Anyway it's a good ideal through.
Notify just sends an email whenever someone posts on the topic, whetehr they reply to you or not.
It should be something refined like "Mentions" where you're notified only when someone either quotes you or
mentions your name on a post.