Web Forms candidate notification not being sent

We are having an issue with the Candidate notification not being sent when they register via a Web Form. The rest of the workflow is operating correctly, i.e. the user is added to Zoho, the owner gets notified. I checked the email history of some test candidates and there is no record of an email being sent. We have only just launched the website and started using this feature. I know it worked when I was testing it a month or so ago. I have attached a screen shot.