Why are we not receiving email notifications?

Also we using an online registration form for our racing events. They used to get a notification when they would submit it online from our website. They no longer get notification.

I have checked the email history for your recipient and I can see all emails are being sent without any problem, you could also check your email history by following this guide: https://www.jotform.com/help/293-How-to-View-All-Your-Form-Email-History 

I would also suggest you to follow this guide in order know why emails may not be sending: https://www.jotform.com/help/364-Why-I-am-not-Receiving-Email-Notifications 

You may also try whitelisting our IP addresses so you avoid emails being blocked: https://www.jotform.com/help/145-Whitelisting-JotMails-IP-Addresses 

Hope this helps.