I thought as much.. Ok, the link below references the exact issue your havinghttp://support.apple.com/kb/TS2621
We ran through the accepted and suggested repair steps, and we werent able to resolve the issue.
Im not saying that were out of hope, but were on experimental territory here.
What im going to suggest, is that you run through the process to update to the new outlook version of bigpond email.
The entire process is shown below.. This will get all your devices working correctly, as outlook will allow all devices to work at the same time without issue.
Once updated, the page has steps to show you how to update your email settings on your mac.
And at the end, also on your ipad / iphone.
If you run into any issues carrying out these steps, please send a reply and let me know. But whats for certain is that once you are fully upgraded to the new version of bigpond email, you wont have this issue any more.
If my answer helped, please click one of the smiley faces to rate the solution, and then click the green submit button to rate the answer. We can still communicate after rating, as rating does not end the conversation.