Online shopping hub Grays has been slugged with a $165,000 fine for not complying with spam regulations.
An Australian Communications and Media Authority (ACMA) investigation found Grays NSW, the company behind GraysOnline, was incorrect when it decided an email campaign was not promotional.
The campaign introduced its GraysEscape website.
The decision allowed Grays to send hundreds of thousands of emails without an opt-out facility for recipients and to some people who had already withdrawn their consent to receiving marketing material.
GraysOnline is a retail and auction site selling goods - including wine, cars and furniture - direct from manufacturers and distributors.
Under the Spam Act, all marketing emails must be sent with a recipient's consent and include an opt-out option.
ACMA deputy chairman Richard Bean said the case demonstrated the domino effect one wrong decision could have.
"This conduct involved a conscious decision by an experienced e-marketer," he said in a statement.
"The consequences of getting it wrong can be severe, from potential penalties such as this, to damaging your reputation."