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Is your account a BigPond email account, or is it a Telstra account?
Accounts can be closed, unfortunately, for simple reasons of having been reported to be sending too many emails at once... or, to be 'spamming' as it's called.
Telstra has this to say:
We’ll email you with your exact move date and the steps you’ll need to follow to move to Telstra Mail™
We will notify you of the date your move is scheduled and then send a confirmation email once your move to Telstra Mail™ is complete. If we have been unable to move you within 48 hours we’ll send you an email to advise you of a rescheduled date. This will be sent to your Telstra or Bigpond email address and to any nominated email address you have supplied to Telstra.
So... have you supplied any nominated address to Telstra ?