Hello Squashy,
As Yastiandrie mentioned above, please confirm that your Bigpond email settings are correct in the client you are using to access your emails at the following link - https://www.telstra.com.au/support/category/email/set-up/imap-pop-and-smtp-information-for-manual-email-set-up
If you require assistance recovering either detail of your Bigpond Email account (Username of Password)
Forgotten Username: https://myacct.bigpond.com/forgottenUsername?execution=e5s1
Forgotten Password: https://myacct.bigpond.com/forgottenPassword?execution=e6s1
Please let me know if this helps
Regards