Google has announced that they are to buy Postini Inc for US$625m, adding a range of email security programs to its offering for small businesses. Postini is a California-based company that operates data centers to process and protect customers' e-mails and instant messages, with a reported 11 million users at 35,000 firms.

This acquisition will help to bolster Google's Gmail service and make it more attractive to businesses, with Google taking another step to challenge Microsoft on the email front and to broaden its web-based applications. This is Google's second largest purchase this year after the Doubleclick acquisition in April.