From Reuters: A new email client unveiled by Mozilla this week contains code from an unusual source — the French military, which decided the open source product was more secure than Microsoft’s (MSFT.O) rival Outlook…

The military found Mozilla’s open source design permitted France to build security extensions, while Microsoft’s secret, proprietary software allowed no tinkering…

The Gendarmerie Nationale police, which was part of the military at the time and did the design, released some of its work to the public under the name “TrustedBird,” and co-branded it with Mozilla. The military uses Mozilla’s Thunderbird mail software and in some cases the Trustedbird extension on 80,000 computers and it has spread to the ministries of Finance, Interior and Culture…

“The primary changes (the military) have made allow them to know for sure when messages have been read, which is critical in a command-and-control organisation,” said David Ascher, chief executive of Mozilla Messaging.

That qualifies it for NATO’s closed messaging system, and the French military has shown TrustedBird to NATO, military officials said. (graphic: French Ministry of Defense)