At present (25/2/2019) Bigpond is marking our emails as sent and saying everything went well but not actually passing the emails on to the end recipient.
Easiest way to do this fix on your Bigpond email.
Go here http://email.telstra.com
Go to Settings (top right next to logout)
Go to Mail (left hand menu)
Go to Safe Senders (just under where you clicked Mail)
Add [email protected] as a safe sender