Logstash email output

I'm trying to send an email using logstash, however logstash keep sending the same email every minutes. The output configuration as per below. Any ideas what went wrong?

output {
email {
  to => "zyx@gmail.com"
  body => "Here is the event line that occured: %{message}"
  address => "smtp.gmail.com"
  port => 587
  username => "xyz@gmail.com"
  password => "mypass"
  use_tls => true
}

The schedule is usually defined by the input.
If your input is the same very minute then logstash will output the same thing every minute.
Does your input run every minute? Is it the same input?

Have you tested this with just writing to a file first before sending an email?