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Relevant to Moodle 3.4 from September 2018 onwards 

How to:  change email settings for forums 

You will always get emails when a module convenor posts Announcements as you are automatically subscribed and cannot unsubscribe..  Other forums are generally set up so that both staff and students can choose whether or not to receive email alerts when someone posts.  To change whether you receive posts by email or not:

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