The FBI did not serve the subpoena directly to Proton Mail.
"We want to first clarify that Proton did not provide any information to the FBI, the information was obtained from the Swiss justice department via MLAT," said Proton AG's head of communications, Edward Shone. "Proton only provides the limited information that we have when issued with a legally binding order from Swiss authorities, which can only happen after all Swiss legal checks are passed. This is an important distinction because Proton operates exclusively under Swiss law."
Proton is incorporated and headquartered in Switzerland, meaning your data is protected by some of the world's strictest privacy laws.
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From newsrooms, activists, and international organizations to academics, Nobel Prize winners, and movie characters, Proton Mail is the trusted choice for secure and private communication.
The FBI did not serve the subpoena directly to Proton Mail.
https://www.msn.com/en-us/travel/news/privacy-focused-proton-mail-handed-protester-data-to-police/ar-AA1XH3R5
Meanwhile, on Proton's homepage: