Google’s acquisition of e-mail security vendor Postini is paying off for Google Apps enterprise users, who today are gaining free access to extra security and compliance features.

The Google Apps Premier Edition will remain at its current price tag of $50 per user, per year, despite significant upgrades based on Postini’s software-as-a-service offerings, Google officials say. Google is also upping Gmail capacity for Premier Edition users from 10GB to 25GB.

“This is virtually unlimited storage,” says Matthew Glotzbach, head of products for Google's Enterprise group.

Both moves could help Google compete against the Microsoft Office set of workplace tools, which has long dominated the business market. Google is quickly ramping up the feature set for Apps Premier Edition, says Gartner analyst Tom Austin, who says he counted 37 significant enhancements to the software-as-a-service platform between February and June.

“I would be very surprised if there isn’t another major announcement from Google this month, two more in November . . . and on and on,” Austin says.

Google added a presentations application last month to Apps, which already included e-mail, calendaring, instant messaging, voice chat, documents and spreadsheets.

Gmail already had spam and virus blockers, but now Google Apps Premier Edition gives businesses new configurable options, such as a whitelist and centrally managed content policy to filter messages that contain certain words or attachments. The Postini features also let administrators add footers to every outbound message, so you don’t have to rely on employees adding text describing e-mail confidentiality policies, Glotzbach says.

“There’s a whole realm of legal compliance around tagging messages in different ways,” he says.

Companies can use the new features to block outgoing messages that mention particular products, competitors or employee names, or spreadsheets that have proprietary financial data, Glotzbach says.

“This is really an enterprise class system that gives a tremendous amount of flexibility and control to IT administrators to define those content policies,” he says.

Postini services fit well with Google Apps, because they are also offered in the software-as-a-service model, he says.