Dubbed Key Transparency, the system uses a “pure form” of blockchain rather than the cryptocurrency Ponzi scheme form.  

Proton CEO and founder Andy Yen said that the platform solves the thorny issue of ensuring that every email address belongs to the person claiming it.

Proton Mail uses end-to-end encryption and can senders encrypt an email using their intended recipient's public key -- a long string of letters and numbers -- which the recipient can then decrypt with their private key.

Yen said the issue is ensuring that the public key belongs to the intended recipient.

"Maybe it's the NSA that has created a fake public key linked to you, and I'm somehow tricked into encrypting data with that public key," he said.

Blockchains are an immutable ledger, meaning any data initially entered into them can't be altered. Y

Yen realised that putting users' public keys on a blockchain would create a record ensuring those keys belonged to them -- and would be cross-referenced whenever other users send emails.

"For the verification to be trusted, it needs to be public, and it needs to be unchanging," Yen said.