Hillary Clinton wrote 104 emails using her private server as secretary of state that the State Department has since designated as classified, an analysis released Sunday found.

Recipients included diplomats, top administration officials and foreigners who did not hold security clearance in the U.S., according to the report published by the Washington Post. Clinton initiated some of the exchanges, but was most often responding to messages sent to her.

The analysis found that an additional 300 emails on Clinton's server written by other parties also contained what State has since designated as classified information. Some of those involved low-level State Department employees who similarly violated federal policies by using improper accounts to send the messages.

Jacob Sullivan, a foreign policy aide who now advises Clinton's presidential campaign, was the most prolific author of classified content, sending a total of 215 emails covered in the analysis. Other authors included Clinton chief of staff Cheryl Mills and deputy chief Huma Abedin.

Federal policies dictate that classified data should only be sent over certain accounts on government networks. The analysis, based on 2,093 chains of Clinton's correspondence that the State Department has deemed classified, did not include 22 emails classified "top secret," the agency's highest level of classification.

Responding to the report, Clinton spokesman Brian Fallon said the information was not designated as classified at the time it was originated by Clinton.

The designation came "after-the-fact," Fallon said, "for purposes of preparing these emails for release publicly."

"It does not mean the material was classified when it was sent or received," Fallon said.

Federal law prohibits the mishandling of classified information regardless of when classification takes place. The State Department has upgraded the classification level on more than 2,000 emails over the last eight months.

Though Clinton and her allies have argued the information is being overclassified by the State Department, the agency has stood by its process. The department has not expressed a judgment on whether the information should have been classified at the time it was being improperly handled.