If you configure SMTP in Grafana that ships with Ambari and enable email notifications, new users who are added to Grafana will be able to receive a "New User" email notification. Apart from that, grafana will not be able to send email notifications on alerts as this feature is only supported in Grafana v4.0 and above.
Configuring SMTP for Ambari will let you receive email notifications on alert status changes on configured groups and severity levels. For example: if two alerts go CRITICAL, Ambari sends one email that says "Alert A is CRITICAL and Ambari B alert is CRITICAL". Ambari will not send another email notification until status has changed again. More details on configuring SMTP for Ambari is presented here - https://docs.hortonworks.com/HDPDocuments/Ambari-220.127.116.11/bk_ambari-operations/content/creating_or_ed...