When you have the Bigpond mail and you notice that certain emails have disappointed you by reaching the outbox, it is mostly a case of the configurations that were set on the SMTP outgoing mail server (SMTP) settings or the network connection. First, check the internet; if it is weak or has been disconnected, that would mean emails would not be sent out. Others are outbound server settings.
If you are using an email client such as Outlook or the Mail app, you will need to check that smtp.telstra.com is the server you are using, Port 465 or 587, with SSL secured. In addition, ensure that the outgoing mail server settings correctly include your email and password. Where the issue persists, it may be that clearing the outbox by deleting emails and sending them again might address the concern.
It sounds rather rudimentary, but log off and log on to your email client or switch off your device or app in a bid to restart them, as these are sometimes competent ways of curing the trouble in sending emails. Also, if the issue persists, it is advisable to re-add your Bigpond email account, which in most cases addresses outbox issues due to the reconnection established to the server.
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