A new Throttle feature was added to the Email Extension plugin in version 1806.v856a_01a_fa_39a_ by https://github.com/jenkinsci/email-ext-plugin/pull/458. But the throttle is not configurable.

The throttle is for 100 email an hour. In some environment, this limit is too short. But at the moment not configurable and this produces an unexpected Could not send email. Throttling limit exceeded. errors upon upgrade to this version of the plugin.

The throttling settings should be configurable.

Workaround

As suggested in the PR, the use the following script:

EmailThrottler.instance = new EmailThrottler() {
  public synchronized boolean isThrottlingLimitExceeded() {
    return false;
  }
}
return

This should work live and could be used as a Post Init groovy script as well.