The investigators appeared to want to finish the inquiry quickly and move on, the former officials said. At some point during Mr. Tillerson’s tenure, people who had heard of the investigation thought it had ended because the diplomatic security bureau no longer appeared to be actively pursuing the question, the officials said.
Mike Pompeo took over as secretary of state in April 2018, and in recent months the diplomatic security bureau has been interviewing current and former employees again about their email use under Mrs. Clinton, the former officials said.
Before joining the Trump administration, Mr. Pompeo was a Republican member of the House, and served on the committee investigating the deadly raid on the American diplomatic compound in Benghazi, Libya. Mr. Pompeo was among those who aggressively questioned Mrs. Clinton.
The Justice Department inquiry into her use of a private email server had its roots in that congressional investigation, which brought to light Mrs. Clinton’s email practices.
The former officials who described the current inquiry on Sunday did so on the condition of anonymity, given the sensitivity of the matter. The State Department did not reply to a request for comment on the current investigation.
Looking to future prospects of the inquiry, the diplomatic security bureau could decide to make a formal note in a person’s file saying he or she had mishandled classified information, according to the former officials. That could lead to that person being unable to get proper security clearances in the future, or the applicant might have to wait a long time for those clearances to be approved.
The former officials said scrutinizing the employees over their handling of information that was not classified at the time, and only retroactively classified, was unusual.
Also, many of those emails summarize conversations with foreign officials who themselves have no security clearance in the United States government, yet are engaged in discussions about topics of interest to American counterparts. In many cases, the emails that went to Mrs. Clinton were part of a long email chain created by officials forwarding emails to one another.
Matthew Rosenberg contributed reporting.