Financial services provider CommSec will pay the media watchdog $55,000 and review its emailing systems after customers complained it was sending them spam.
The Australian Communications and Media Authority launched an investigation after receiving complaints that CommSec was continuing to send commercial emails to people who had opted out of the service.
ACMA also found CommSec's email campaigns in January, February and March 2009 did not provide customers the option to opt out of receiving emails.
"ACMA expects that Australian businesses take note of this outcome," ACMA chairman Chris Chapman said.
"Under the Spam Act, every person has the right to unsubscribe from receiving commercial electronic messages and to have that request acted on effectively and quickly.
"The failure to act on a request can result in significant penalties if a business is found to have breached the Act."
As a result of ACMA's investigation CommSec has begun a review of its system and processes, while an independent consultant will assess the review and the company's email campaigns for a year.
CommSec will also pay ACMA a financial component of $55,000, Mr Chapman said.
AAP