User subscription settings
When a user is subscribed to a forum it means that they will receive notification (via popup and/or email, depending on the user’s messaging settings preferences) of each new posting. By default, posts are recorded about 30 minutes after the post was first written. Depending upon the email settings of each forum member, they may be sent an email immediately after the 30 minute edit window is closed, or in a batch at a time fixed by the site administrator. (from moodle.org)
there are two areas that users can use to manage subscription preferences. Each is outlined below.
Area 1: My Profile Settings:
From your course home page select Administration > My profile settings > Edit profile and ensure the Forum auto-subscribe feature is set the way you want.
Area 2: Forums:
Provides the option of subscribing or unsubscribing to all forums or individual forums based on the options selected by the instructor when setting up the forums.
To view all the forum subscription settings select “Forums” from the Activities block.