Thank you for writing back. I believe you need to reinstate your bigpond account. But before that you need to backup your PST file since this file stores ALL of your Outlook data. Create a copy of this PST file into a safe location as backup.
Open Outlook and then go to Tools => Account Settings. Click on Data Files tab to see all your PST file.
In the list, please locate the PST file for your Personal Folder. The other folder might be Archive.
When found, please click on the line where it shows PST at the end. Then click Open File Location button at the top.
Then locate the actual PST file in the new explorer window that opens. It is called Outlook.pst file by default and has an icon similar to MS Outlook. If your files does not show the extensions, then the Type column must be Outlook Data File.
When found, copy that PST file to any location like My Documents for backup.
When done, close MS Outlook all all windows, then follow the steps described in this link to create a NEW Email Profile:http://www.technicalforum.org/windows/how-create-new-mail-profile-windows-7
After creating a new email profile, you will need to add your bigpond account again to your Outlook but do not worry, all your old emailas are intact. Just add your bigbond again in this new email profile and then see if it will send without any issues.