The finding is the first accounting of the Democratic presidential front-runner’s personal role in placing information now considered sensitive into insecure email during her State Department tenure. Clinton’s ­authorship of dozens of emails now considered classified could complicate her efforts to argue that she never put government secrets at risk.

In roughly three-quarters of those cases, officials have determined that material Clinton herself wrote in the body of email messages is classified. Clinton sometimes initiated the conversations but more often replied to aides or other officials with brief reactions to ongoing discussions.

The analysis also showed that the practice of using non-secure email systems to send sensitive information was widespread at the department and elsewhere in government.