Just going to put this link from Legal Vision here for future reference.
I come up against this all the time with customers – they collect business cards at tradeshows and events and immediately add the contacts to their email newsletter list.
It can be a bit of an awkward discussion, but it should be clear:
The question is whether a person providing their business card is consent to receiving commercial electronic messages. Under Schedule 1 of the Act, consent is either express or reasonably inferred from the conduct and business relationship of the individual or organisation concerned.
Australian Communications and Media Authority v Clarity1 Pty Ltd (ABN 60 106 529 604) and Another (2006) 229 ALR 658
Summary: don’t send emails to people who haven’t given you their consent. And if you have to ask for clarification on whether they’ve given you their consent, assume they haven’t.