Notifications not going through

After talking to both our email host and web host companies, we cannot figure out why notifications to anyone using the @medicalcost.com domain are not going through. I’ve added my own personal email as a BCC on the notification and I am getting them fine. It’s only emails that use the same domain as the web site that are not getting through. Can you please help us?

The page I need help with: [log in to see the link]