The digital postbox venture was valued at US$4.2 million ($4 million) as of December 2012, according to the firm's half-yearly results. It was valued at US$695,000 in June 2012.

Within that period, Computershare bought out the 40% stake of launch partner Salmat.

Chief executive Stuart Crosby said in a statement: "In December 2012, we increased our investment in Digital Post Australia to 80%. During the last half we conducted a successful private launch and look forward to the public launch in the coming months."

Computershare, whose core business is share registry services, posted a net profit of US$94.6 million for the six months to 31 December 2012, a 15.2% year-on-year decline. Revenue rose 26.1% to US$977 million on the back of acquisitions, but profit margins fell from 14.4% to 9.7%. Net debt fell 0.9% to US$1.3 billion.

Its international print and mail division, Computershare Communication Services, grew revenue 8.9% to US$98.3 million. Within this, its Australia and New Zealand print and mail business increased sales by 4.8% to US$74.4 million.

"Although the Communication Services market [in Australia and New Zealand] remains tough we continue to see opportunities, especially in leveraging our inbound capabilities," said Crosby.

[LinkedIn: Will digital mailboxes kill off printed post?]

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