Emmanuel Macron’s digital team responded to cyberattacks with a “cyber-blurring” strategy that involved fake email accounts loaded with false documents.
[…]
“We created false accounts, with false content, as traps. We did this massively, to create the obligation for them to verify, to determine whether it was a real account,” Mr. Mahjoubi said. “I don’t think we prevented them. We just slowed them down,” he said. “Even if it made them lose one minute, we’re happy,” he said.
[…]
But he did note that in the mishmash that constituted the Friday dump, there were some authentic documents, some phony documents of the hackers’ own manufacture, some stolen documents from various companies, and some false emails created by the campaign.

Source: Hackers Came, but the French Were Prepared

What this does – which is more important – is it puts the onus on the leakers / hackers to verify the contents of their data, which is a big deal, as this is hard to do and time consuming. As soon as any doubt is seeded on the authenticity on even one of the documents in a leaked trove, the whole of the trove massively loses value.