The report by the state department's independent inspector general cited "longstanding, systemic weaknesses" in how Clinton and four of her predecessors managed the security of their emails.
"Secretary Clinton should have preserved any Federal records she created and received on her personal account by printing and filing those records with the related files in the office of the secretary," said the office of inspector general of the state department in the report to the Congress.
"At a minimum, Secretary Clinton should have surrendered all emails dealing with Department business before leaving government service and, because she did not do so, she did not comply with the department's policies that were implemented in accordance with the Federal Records Act," the report said.
The inspector general said sending emails from a personal account to other employees at their department accounts is not an appropriate method of preserving any such emails that would constitute a Federal record.
During her term as the secretary of state from January 21, 2009 to February 1, 2013, Clinton did not use a department email account and has acknowledged using an email account maintained on a private server for official business, it said.
"In December 2014, her representative produced to the department 55,000 hard-copy pages of documents, representing approximately 30,000 emails that could potentially constitute Federal records that she sent or received from April 2009 through early 2013," it said.
"Clinton’s representative asserted that, because the secretary emailed department officials at their government email accounts, the Department already had records of the secretary's email preserved within its record-keeping systems," it noted.
Clinton is the front-runner to secure the Democratic Party nomination to run in November's presidential election, but her campaign has been marred by criticism of her decision to conduct diplomatic business on a private email account.
The opposition Republican Party was quick to slam Clinton after the report issued by the state department's inspector general.
"The inspector general's findings are just the latest chapter in the long saga of Hillary Clinton's bad judgement that broke federal rules and endangered our national security," said Republican National Committee chairman Reince Priebus.
"This detailed inquiry by an Obama appointee makes clear Clinton hasn't been telling the truth since day one, and her and her aides' refusal to cooperate with this probe only underscores that fact," he alleged.