It is understood that SEMA, which handled the printing and mailing of the letter discussing upcoming fixed line price changes, was supplied with incorrect data by the telco.

A Telstra spokesperson confirmed to ProPrint that the error occurred within Telstra’s internal operations.

“The error happened before printing and mailing,” he said.

SEMA executive director Brent McCulloch told ProPrint: “SEMA have contributed no faults to this issue. It’s a Telstra issue, and we’ll be working with Telstra to rectify that.”

The mailing list error meant around 220,000 letters with incorrect addresses were mailed out, including 23,500 letters involving customers with silent lines.

According to Telstra, the mail-out was stopped as soon as the error was identified. The telco emphasised that, while the letters contained customers’ names, telephone plans and phone numbers, no billing or call record information was disclosed.

“Telstra is taking this issue very seriously.  An urgent and thorough investigation is underway to examine how this occurred and to stop it happening again,” the company said.

Telstra said it is co-operating with the Privacy Commissioner, regulatory authorities and consumer groups in investigating the mistake. Customers who have received multiple letters are requested to securely destroy them or return to sender.

Neither Telstra’s print manager Fox Print Solutions nor regular billings supplier Salmat were involved in the mail-out.

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