I deployed Prometheus and Grafana in our Kubernetes cluster. On the Grafana server web page, I clicked on the “Send Test” from Alerting Notification channels. But, I do not receive any email from Grafana server. I think I need to deploy SMTP server into Kubernetes cluster, configure the SMTP and Grafana servers to enable Grafana sends out email. Are there any instructions or links that tell how to deploy a proper SMTP server, and configure Grafana inside Kubernetes cluster to make Grafana sends out email?