I contacted my webhost and it turns out this was an issue with my cPanel settings. I use 3rd party DNS management so I needed to change my mail exchange settings in cPanel. See below the advice from my webhost support team:
As your domain uses 3rd party DNS, our server doesn’t know to automatically flick the switch in attempting to deliver mail for adamjaffrey.com externally. To address this issue, simply login to your cPanel > goto MX Entry > Set Mail Exchanger to Remote. Once set, this will resolve your issues immediately.
FYI, this fixed my issue immediately in its entirety! ??
