"We need more security on our messages to prevent possible espionage," Rousseff said on Twitter, ordering the Federal Data Processing Service, or SERPRO, to implement a safe email system throughout the federal government.
The agency, which falls under Brazil's Finance Ministry, develops secure systems for online tax returns and also creates new passports.
The move came after Rousseff publicly condemned spying against Brazilian government agencies attributed to the United States and Canada.
"This is the first step toward extending the privacy and inviolability of official posts," Rousseff said.
After bringing her complaints against US intelligence agencies to the United Nations General Assembly last month and canceling a state visit to Washington, Rousseff announced that the country will host an international conference on Internet governance in April.
In recent months, Brazilian media outlets have published documents showing that the US National Security Agency's spied on Rousseff's official communications, her close associates and state-controlled oil giant Petrobras.
The information was revealed by Edward Snowden, a 30-year-old former NSA contractor who has sought refuge in Russia and is wanted by the United States after revealing details of the agency's massive snooping activities.
For the latest tech news and reviews, follow Gadgets 360 on X, Facebook, WhatsApp, Threads and Google News. For the latest videos on gadgets and tech, subscribe to our YouTube channel. If you want to know everything about top influencers, follow our in-house Who'sThat360 on Instagram and YouTube.