Alertmanager failing in email receiver at certificate validation

Issue

• Alertmanager is failing to send alerts using email receiver with certificate validation errors like:

  level=warn component=dispatcher receiver=MyEmailReceiver=email[0] msg="Notify attempt failed, will retry later" attempts=1 err="send STARTTLS command: x509: cannot validate certificate for <SMTP_ip_address_here> because it doesn't contain any IP SANs"
  

  level=warn component=dispatcher receiver=MyEmailReceiver=email[0] aggrGroup="{}:{namespace=\"[namespace_name]\"}" msg="Notify attempt failed, will retry later" attempts=7 err="send STARTTLS command: tls: failed to verify certificate: x509: certificate has expired or is not yet valid: current time 2026-01-01T00:00:00Z is after 2025-12-31T23:59:59Z"