The warnings were issued during mandatory ethics training sessions held for White House personnel in the past several weeks. During the hour-long briefings, deputy counsel Stefan C. Passantino told staffers to use only White House email for work communications and not any unofficial platforms such as smartphone apps, texts and private emails, according to several people in attendance.

Using such messaging services for official government business could violate the Presidential Records Act, which requires that nearly all official White House correspondence be preserved.

Some participants at the ethics sessions in the Old Executive Office Building said Passantino suggested that there had been inappropriate use of smartphone apps such as WhatsApp.

“He did focus on WhatsApp — said that people were using it, and it wasn’t appropriate,” said one staffer who attended a recent briefing and requested anonymity to describe the discussion. “He said, ‘All those apps are a big problem.’ ”