The details of more than 28,000 Melbourne IT customers have been emailed to others in an embarrassing privacy breach by the domain registrar.

Each year the registrar is obliged by the Internet Corporation for Assigned Names and Numbers (ICANN) to send a reminder to customers to ensure it keeps registrant information up to date for each registered domain.

It began sending the notifications to 350,000 customers in batches on Thursday, before it realised one of the batches had been emailed to customers other than the relevant domain owners or their representatives.

Melbourne IT was Australia's first domain registrar, it now also offers web hosting, web design and IT services to small and large corporate and government clients.

The public company's general manager of corporate communications, Tony Smith, told IT Pro late on Friday that a single "batch contained erroneous information which resulted in some customers being sent reminder notices meant for other customers."