The ABC reported that for 11 months, emails from the accounts of three Australian employees had been forwarded to a source outside the company.
But it also claimed that the sensitive personal information of about 500 employees was affected.
The forwarding of email apparently began on 27 May last year; accounts in finance, payroll and operations were affected.
The NDB scheme makes it mandatory for Australian Government agencies and other bodies that are obliged to comply to secure personal information under the Privacy Act 1988 (Cth) and notify individuals who are affected by data breaches that are likely to result in serious harm.
The ABC quoted Svitzer's head of communications, Nicole Holyer, as saying the company was alerted to the breach on 1 March. She said that between 50,000 to 60,000 emails may have been exfiltrated.
It claimed the data that was exfiltrated could have included tax file numbers, superannuation accounts numbers and names of next of kin of staff.
"Our absolute priority is our employees. We are offering the highest levels of support to those affected," Svitzer Australia managing director Steffen Risager was quoted as saying in a statement.
"Svitzer's IT help desk received a call from an employee about a suspicious email rejection notice from an external email account," she said.
"We then identified, after an investigation, that an email rule had been created on three Svitzer Australia employee accounts to automatically forward emails to two external email accounts."
The Office of the Australian Information Commissioner was informed about the breach on Thursday.