Google ramped up its challenge to Microsoft’s domination of office software tools by more than doubling the storage capacity of its corporate e-mail service and unveiling new security features.

Google increased the storage capacity of each individual corporate mailbox offered under its paid-for Google Premier Apps bundle of services to 25 gigabytes, up from 10 gigabytes.

The group unveiled the package of software tools in February, offering businesses a bundle of web-based services, accessible over the internet, for $50 (£25) a year per user.

Google’s tools, which include a word processor and spreadsheet, compete with Microsoft’s Office software.

Since then Google has added a new presentation tool squarely aimed at Microsoft's PowerPoint application and signed a partnership with Capgemini, the IT outsourcer, which gives it access to some one million corporate desktops.

Yesterday Google also added security features acquired through its purchase of Postini, the antispam specialist that Google bought this year for $625 million.

Tom Austin, the Gartner analyst, said that the upgrade signalled Google’s ambition to wean customers away from stalwart Microsoft products such as Outlook, its rival e-mail system.

“These are all just pixels in a much bigger picture,” he said.

“Google is really trying to shake up the assumptions of people and move the industry to an entirely different model.”

In recent weeks three rivals – IBM, Google and Yahoo! – have all given notice of their intentions to compete head-on with Microsoft Office, recently the software giant’s biggest earner by far.

The suite of office tools, which also includes Word and Excel, accounted for revenues of $4.6 billion – a third of Microsoft total sales – in the company’s most recently reported quarter.

Much of the threat comes from software given away free over the internet – a dramatic departure from Microsoft’s licence-based model, in which software is hosted on a user's desktop machine.

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