France’s electoral commission has said any organisations that circulate information from the leaked messages may be committing a criminal offence.
On Friday, Mr Macron’s campaign team confirmed it had fallen victim to a “massive hacking attack” which resulted in hundreds of internal documents being dumped online.
About nine gigabytes of data was posted by an anonymous user called EMLEAKS, only hours before the end of official election campaigning.
The En Marche! party has said the files only showed the normal functioning of a presidential campaign, but claimed fake documents were being circulated alongside authentic ones in order to sow “doubt and misinformation”.
Aides have alleged those behind the cyberattack were attempting to destabilise Sunday’s final round between Mr Macron and his far-right rival Marine Le Pen.
The officials drew comparisons with the emails leaked from Hillary Clinton’s campaign in the run-up to last November’s presidential election in the US.
“We knew that this kind of risk would be present during the presidential campaign, because it has happened elsewhere. Nothing will be left without a response,” French President Francois Hollande told French news agency AFP.
Recent opinion polls have forecast that Mr Macron will win the second round with 62% of the vote.
In the days prior to the cyberattack, the front runner’s campaign had made repeated complaints that unsuccessful attempts were being made to compromise its email accounts.
Mr Macron’s team had suggested that Russia may have had an interest in orchestrating the cyberattacks, but the Kremlin has denied any involvement.
Vitali Kremez, a cyber intelligence expert, told the Reuters news agency that Moscow’s involvement in the leak would mark “a significant escalation over the previous Russian operations aimed at the US presidential election, expanding the approach and scope of effort from simple espionage efforts towards more direct attempts to sway the outcome”.
Ben Nimmo, a UK-based security researcher, said initial analysis suggested that online activists affiliated with American far-right groups had been behind early efforts to spread the leaked Macron emails on social media.
Following this, the documents were seen and promoted by social media users who back Ms Le Pen.
Mr Macron has been fighting battles on several fronts in recent days. Earlier in the week, he filed a legal complaint over rumours he has an offshore account in the Bahamas – claims which were repeated by Ms Le Pen during a TV debate.
The 39-year-old centrist, who has never held elected office, described her remarks as “defamation”.
Meanwhile, his campaign described it as a “textbook case of fake news”, and said the unfounded reports about his financial affairs had been spread by Kremlin-friendly media organisations and President Trump’s supporters.