Mail destination (with secure settings)

Add these settings to elasticsearch.yml :

opendistro.alerting.destination.mail.host: "localhost"
opendistro.alerting.destination.mail.port: 25
# Connexion method : "none", "ssl" or "starttls"
opendistro.alerting.destination.mail.method: "none"
opendistro.alerting.destination.mail.from: "test@localhost"

If authentification needed, add these settings to elasticsearch keystore :

elasticsearch-keystore add  opendistro.alerting.destination.mail.username
elasticsearch-keystore add  opendistro.alerting.destination.mail.password