For months, the U.S. State Department has stood behind its former boss Hillary Clinton as she has repeatedly said she did not send or receive classified information on her unsecured, private email account, a practice the government forbids.

While the department is now stamping a few dozen of the publicly released emails as "Classified," it stresses this is not evidence of rule-breaking. Those stamps are new, it says, and do not mean the information was classified when Clinton, the Democratic frontrunner in the 2016 presidential election, first sent or received it.

But the details included in those "Classified" stamps — which include a string of dates, letters and numbers describing the nature of the classification — appear to undermine this account, a Reuters examination of the emails and the relevant regulations has found.

The new stamps indicate that some of Clinton's emails from her time as the nation's most senior diplomat are filled with a type of information the U.S. government and the department's own regulations automatically deems classified from the get-go — regardless of whether it is already marked that way or not.