https://docs.openshift.com/container-platform/4.16/observability/monitoring/troubleshooting-monitoring-issues.html 

This has been discussed previously - adding content from the following KCS into the mainline docs - https://access.redhat.com/solutions/6984635 

In the past I think we agreed that the best place for this content was a runbook rather than the troubleshooting page - the runbook would be for the alert "AlertmanagerReceiversNotConfigured"

For me the important statement that is currently missing from our docs is: 

• Alertmanager does not support unencrypted connections to remote SMTP endpoints
• The Go package smtp.Sendmail used by Alertmanager does not support unencrypted connections