It looks like Google's acquisition train just keeps going. Yesterday they announced the purchase of Postini, a major corporate security and spam filtering company, for $625 million. The press release says that Google is looking to include this in their Google Apps strategy with Gmail, Calendar, Talk, and Docs and Spreadsheets. Google plans to use Postini's expertise to add security, archiving, policy enforcement to their apps.

Postini is well known for providing spam filtering, anti-virus, encryption, archival and compliance services for email. They also provide instant messaging and web security services.

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

Google and Postini are both heavy believers in SaaS (Software as a Service) and that IT shops are wanting to outsource as much as they can if the price is right. Postini currently has over 11 million users and has been profitable since 2004.