Check the setting called “Enable mailing list mode” on the Emails page in preferences. If this is ticked then you will receive a lot of e-mails. There’s also a setting on that page for a daily summary.
The terminology Discourse (our forum software) uses for this can be confusing. For any topic/category/user you can be either
Tracking: this means you see a badge showing the number of unread posts. It shouldn’t send you e-mails. By default, any topic you read for more than 4 minutes will be set to tracking.
Watching: you will receive e-mails when anything new happens on that topic.
You can see the list of things you are watching and tracking under Notifications > Categories then “Show watched topics” or “Show tracked topics”.