The Minister for Information Technology and Communications, Daryl Williams, said in a statement that the legislated grace period would give businesses "time to adjust their practices where necessary".
Those businesses who persist in sending spam messages from that date face penalties of up to $1.1m (£0.46m) per day, Williams warned.
The Minister said the Spam Act prohibited the sending of unsolicited commercial electronic messages with an Australian link.
"This means that commercial spam, sent by mobile phone as well as by email, is not permitted to originate from Australia and is not allowed to be sent to Australian addresses, whatever their point of origin".
The legislation will be enforced by the Australian Communications Authority.
Williams also said the National Office of the Information Economy would coordinate a 12-month information campaign about the legislation and about spam, kicking off early in 2004.
However, he conceded that enforcement of the new law against overseas-based spammers would depend on the cooperation of other jurisdictions.
As well as signing an agreement with the Korean Information Security Agency to cooperate on spam-related issues, Australia plans to attend the OECD Workshop on Spam in February 2004, which will discuss multilateral approaches to fighting spam.
