You can manage the email notifications you receive from teams you belong to from the Team section of your profile at https://hackerone.com/settings/teams. From this section, you can view a list of teams you belong to along with the visibility of that team on your public profile and your notification settings.
In order to change your notification preferences, click on the link below "Notifications" (it will read either "Enabled" or "Disabled," depending upon your existing preference). You will then have the option to disable notifications from future reports, or from future and past reports. Click the green Submit button to save your new preference.
When disabled you will only start receiving notifications when you interact with a report, are assigned to a report, or mentioned in a report.