A lead was not sent an email by a Smart Campaign
* Check if the lead has reached the daily or weekly communication limit.
* Check if the lead has a duplicate lead with the same email address that was sent an email already.
* Check if the campaign is set to qualify leads only once. If the lead has ran through the campaign previously when it had different flow steps, then the lead cannot qualify for the campaign again even though the flow steps have changed.
* If all leads in the campaign were not processed, check if there is a campaign restriction.