Logstash email output using linux sendmail

Hi i want to use Linux sendmail service to send email using Logstash email output plugin.
how can i do it.
email {
to => "crazy@noreply.com"
codec => "plain"
body => "hi how are you"
via => "sendmail"
}
Is these are the only information i want but it does not send the email
This is urgent.

Thanks for help.