The federal government, which has some of the most sophisticated antihacking technologies in the world, is offering limited assistance to Mr. Biden’s transition operation in securing its email and other communications, despite concerns that the team is likely a top espionage target for Russia, China, and other adversaries, according to people familiar with the transition.

The lack of government cybersecurity support is among the obstacles the Biden transition team has faced as a result of the Trump administration’s refusal to acknowledge Mr. Biden’s election victory and make available the resources of the federal government ahead of his inauguration in two months.

Normally, the General Services Administration would own and manage the setup of government email accounts for a presidential transition team, which are typically assigned the “ptt.gov” domain. The cybersecurity wing of the Department of Homeland Security typically assists in helping a transition to protect those newly created government email accounts, according to current and former officials, and could rely on information from U.S. intelligence agencies to inform its protective efforts.