This act covers email and faxs - I know it is the case with DIBP (Department of Immigration and Boarder Protection) and it certainly would not surprise many (yourself excluded Lead Balloon) if it is a CASA policy in fine print that if you elect/agree (contact with your signature and date) to communication via email, they have elected option (a) above.
In fact I would assume most if not all Government agencies have it as a default Leady.
(Remember if CASA sent a "fax" on Christmas eve - but the fax did not print - fax was indeed considered received by CASA)
Electronic Transactions Act 1999 (Cth)
Is a faxed message an electronic communication for the purposes of the Act?
Yes, it falls within the definition of ‘electronic communication’ because it is a message sent over phone lines as information. Usually the recipient receives the message through their fax machine in paper form but it can just as easily be received by a computer as an electronic document if the computer is attached to a fax modem. Alternatively, a computer can be used to send a fax to another computer. There will be no paper involved until either the sender or the recipient prints out the fax.