By default, Moodle will email you every time someone posts to a forum to which you’re subscribed, but you have the option to adjust your forum email preferences. To modify the way Moodle sends you email updates on forums, click on “Preferences” in your user menu.
In the next window, click on “Forum preferences” under the “User account” options.
In the “Forum preferences” area, look for the “Email digest type” drop down. Select the option that works best for you. Be sure to save your work.