This needs to be resolved now (if it is not resolved within the next 7 days I am going to bring it to the attention of the 'Telecommunications Industry Ombudsman' (https://www.tio.com.au/).
I have asked the following question twice (in a private email to Telstra Bigpond Support), and both times they responded to my email but did not give me an answer to this question:
Why is it that only the emails I send to people with Bigpond accounts are being delayed by 12 to 24 hours or fail to deliver at all?
If there was anything suspicious or not right about my hardware, software, IP addresses or anything else that I am doing at my end, then you would expect that sometimes the emails I send to other people using other email services (not use Bigpond) would occasionally fail as well. But no, this never happens with the any other email address ONLY EMAILS TO BIGPOND EMAIL ADDRESSES have an issue.
Telstra Bigpond please fix or undo what ever you did to create this problem, because it has created more problems than before.