When a user's email gets suppressed, (this can happen for many reasons, i.e. marking notifications as spam accidentally, file size too big, etc.), they won't receive email notifications to their inbox.
You can now view this and delete the suppression from within the portal. First, search the user then select the settings on the right side.
From here, click "Delete Suppression"
This will remove the suppression from the user's email. We reccommend then sending a test to ensure email notifications begin sending. If your user still isn't receiving email notifications, make sure to check the email notification settings. You can find how a user changes and accesses email notification settings here.