The National Oceanic and Atmospheric Administration has moved 25,000 employees and contractors to Google Apps for Government.
But the agency is also giving its users the flexibility to use a variety of email clients, as well as the option of continuing to use Microsoft Office.
Google announced the NOAA's move to the cloud-based applications in a blog post today.
The migration was completed in about six months, Google said.
NOAA is now using Gmail for all its email, calendaring and docs, according to the agency's CIO, Joseph Klimavicz.
"We did not intend to replace Microsoft Office completely with Google Docs," said Klimavicz in an email response to questions from Computerworld. "We are not requiring users to abandon their mail clients, they may continue to use Outlook, Thunderbird, and Mac Mail."
Previously, NOAA used Sun One messaging and Microsoft Exchange.
NOAA estimated that the move to the hosted system could reduce its messaging costs by 50%, the amount of savings generally touted by government officials about cloud migrations.
The U.S. General Services Administration announced last July that it had become the first federal agency to move to Google Apps for Government.
That agency said it expects to save 50% over the next five years, or about $15.2 million. A large part of the savings is coming from decrease in hardware support and data center services.
U.S. officials have estimated that they will save about $1 million for every 7,500 users who transition to cloud-based services.
Microsoft is also winning federal contracts for cloud-based services.
For example, the U.S. Department of Agriculture has moved some 120,000 users to a hosted version of Microsoft Exchange.
Separately, the city of Pittsburgh announced Wednesday that nearly 3,000 city employees have moved to Google Apps.
The City of Los Angeles, minus its police department, is moving ahead with plans to migrate to Google Apps.
The LAPD dropped its plan to move to Google's cloud-based offerings late last year due to security concerns.
Patrick Thibodeau covers SaaS and enterprise applications, outsourcing, government IT policies, data centers and IT workforce issues for Computerworld. Follow Patrick on Twitter at @DCgov, or subscribe to Patrick's RSS feed . His e-mail address is firstname.lastname@example.org.