Yet another acquisition by Google

Google Inc. agreed to acquire email security company Postini Inc. for $625 million in cash, in a deal that furthers the Internet giant's push into business software.

Postini, which has developed technology for protecting and managing email and instant messages, is based in San Carlos, Ca. The closely held company was founded in 1999 and has funding from August Capital and Mobius Venture Capital.

Postini is one of a host of small companies that offer Web-based services to help businesses clean their email of spam, viruses and other software-related problems. Microsoft Corp. acquired Postini rival FrontBridge Technologies Inc. in 2005 and Symantec Corp. bought another company in the area called Brightmail Inc. for more than $300 million in 2004.

Google has moved increasingly into the business software market by offering a suite of Web-based programs. Earlier this year, Google acquired a company with a Web-based word processor named Writely and released a Web-based spreadsheet application allowing users to collaborate online.

"With this transaction, we're reinforcing our commitment to delivering compelling hosted applications to businesses of all sizes," said Google Chairman and CEO Eric Schmidt in a press release.

The Mountain View, Ca. company, said Postini will become a wholly owned subsidiary and the deal is expected to close by the end of the third quarter.

Earlier this month, Google also agreed to acquire GrandCentral Communications Inc., a start-up that allows users to manage their existing phones and voicemail services over the Web.

Postini represents Google's third largest purchase, following the $1.76 billion purchase of YouTube and the $3.1 billion acquisition of online advertising service DoubleClick Inc.