Why can't grafana send email?

Pull grafana helm chart from official site.

https://github.com/kubernetes/charts/tree/master/stable/grafana

Set email send configuration in values.yaml file:

https://github.com/kubernetes/charts/blob/master/stable/grafana/values.yaml#L363

[smtp]
enabled = true
host = smtp.gmail.com:587
user = sender@gmail.com
password = sender_password
;cert_file =
;key_file =
skip_verify = true
from_address = sender@gmail.com

Then install it at local:

$ helm install grafana

Test send email, failed. Don't know why.