The company has agreed to pay $310,800 for sending out more than 42 million unwanted marketing messages.

Kogan made it difficult to unsubscribe from the emails, requiring customers to set up passwords and log into their accounts.

Australia's communications watchdog has found the company breached the Spam Act, which requires electronic marketing material to contain an unsubscribe function.

Nerida O'Loughlin from the Australian Communications and Media Authority said Kogan's breaches affected millions of customers and frustrated many people.

She said the company was given multiple warnings about its tactics before the official investigation began.

"Businesses must comply with the unsubscribe requirements in the spam rules," Ms O'Loughlin told AAP.

"This investigation makes clear that businesses can't force customers to set a password and login to unsubscribe from receiving commercial messages."

The company has since updated the unsubscribe settings on marketing emails and accepted a three-year, court-enforceable undertaking which will apply to both its Kogan and Dick Smith brands.

It will be required to appoint an independent consultant to review the company's systems and procedures, as well as train staff responsible for sending marketing messages.

Kogan will also need to regularly report to the ACMA on its customer complaints.

Ms O'Loughlin said the significant fine and tough terms of the deal should send a clear message to Kogan and other companies about flouting spamming laws.

Businesses have paid more than $2.1 million over the past 18 months for breaching spam and telemarketing rules.

The ACMA has also accepted nine court-enforceable undertakings and issued 10 formal warnings.

Australian Associated Press