In it, the chief executive officer said that now the antitrust settlement between Microsoft, the US Department of Justice and individual states had been approved, he believed executives and staff were "creating an entirely new Microsoft".
"As CEO, I can personally assure you that Microsoft will commit all the time, energy and resources necessary to follow through on our responsibilities," Ballmer wrote in the e-mail. "We have learned a great deal from our experiences of these past few years, in particular about our responsibilities as an industry leader."
Ballmer said that during the antitrust proceedings, "not everyone in the industry raced to support us [Microsoft]". As a consequence, Ballmer added, Microsoft learned that it needed to take a different perspective on being a good industry leader.
As part of the new approach, Microsoft is co-operating with other companies to develop standards based on XML for communicating across the Web.
"We recognise that we need to support industry cooperation in new and creative ways," Ballmer said. "The entire industry has embraced XML as the universal way for computers to talk to each other in a much richer way across the World Wide Web.
"Today, companies like Microsoft and IBM collaborate on enhancing XML-based standards while at the same time competing to make innovative, easy-to-use software that helps customers take advantage of the power of XML."
The co-operation extended to working with governments on the increasingly important topic of security, as businesses and government rely more heavily on the Internet to conduct business.
"I think we are on the verge of a new era of partnership with government - not just for our company, but for the broader industry," he said. "For example, we're actively co-operating with governments at all levels to fight identity theft, cybercrime and attacks on the Internet, such as the concerted attacks on Domain Name System (DNS) servers last month."