The notifiers from the portal are sent out via a mail profile. If you do not see notifier going out or you are just setting up your portal, follow the Microsoft Documentation to get started. The Database Mail Profile will need to be Public to allow the portal to send out emails.
If the portal has already been installed
Once the database mail profile is configured, log in to the portal and navigate to Admin > Portal Settings > Email Notification Settings. Fill in this setting with the profile name of the SQL Mail Profile (2:04 in the video).