title: How do I tell Prometheus' Alertmanager to send email through Gmail's SMTP server
body: <p>I would like Prometheus to send emails from a Gmail (Gapps) account when metrics cross certain thresholds.
  In the <a href="http://prometheus.io/docs/alerting/configuration/#email-receiver-email_config" rel="noreferrer">Alertmanager config docs</a>, there's no mention of passwords.  How do I authenticate to the SMTP server?  </p>