ProtonMail

On 16 May 2014, ProtonMail entered into public beta.[14] It was met with enough response that after three days they needed to temporarily suspend beta signups to expand server capacity.[15] Two months later, ProtonMail received US$550,377 from 10,576 donors through a crowdfunding campaign on Indiegogo, while aiming for US$100,000.[16] During the campaign, PayPal froze ProtonMail's PayPal account, thereby preventing the withdrawal of US$251,721 worth of donations. PayPal stated that the account was frozen due to doubts of the legality of encryption, statements that opponents said were unfounded.[17][18] The restrictions were lifted the following day.[19]

On 18 March 2015, ProtonMail received US$2 million from Charles River Ventures and the Fondation Genevoise pour l'Innovation Technologique (Fongit).[20] On 14 August 2015, ProtonMail released major version 2.0, which included a rewritten codebase for its web interface. On 17 March 2016, ProtonMail released major version 3.0, which saw the official launch of ProtonMail out of beta. With a new interface for the web client, version 3.0 also included the public launch of ProtonMail's iOS and Android beta applications.[21]

On 19 January 2017, ProtonMail announced support through Tor, at the hidden service address protonirockerxow.onion.[22][23] On 21 November 2017, ProtonMail introduced ProtonMail Contacts, a zero-access encryption contacts manager. ProtonMail Contacts also utilizes digital signatures to verify the integrity of contacts data.[24] On 6 December 2017, ProtonMail launched ProtonMail Bridge, an application that provides end-to-end email encryption to any desktop client that supports IMAP and SMTP, such as Microsoft Outlook, Mozilla Thunderbird, and Apple Mail, for Windows and MacOS.[25]

On 25 July 2018, ProtonMail introduced address verification and PGP support, making ProtonMail interoperable with other PGP clients.[26] In December 2019, ProtonMail launched "ProtonCalendar", a fully encrypted calendar.[27]

The source code for the back-end remains closed source.[28][29] However, ProtonMail released the source code for the web interface under an open-source license.[30] ProtonMail also open sourced their mobile clients for iOS and Android,[31][32] as well the ProtonMail Bridge app.[33] All of their source code can be found on GitHub.

In September 2020, it was known that Protonmail has joined the Coalition for App Fairness which aims to gain better conditions for the inclusion of their apps in app stores.[34]

From 3 to 7 November 2015, ProtonMail was under several DDoS attacks that made the service largely unavailable to users.[35] During the attacks, the company stated on Twitter that it was looking for a new data center in Switzerland, saying, "many are afraid due to the magnitude of the attack against us".[36]

In July 2018, ProtonMail reported it was once more suffering from DDoS attacks. CEO Andy Yen claimed that the attackers had been paid by an unknown party to launch the attacks.[37] In September 2018, one of the suspected ProtonMail attackers was arrested by British law enforcement and charged in connection with a series of other high-profile cyberattacks against schools and airlines.[38]

On 15 November 2019, Proton confirmed that Belarus had issued a nationwide block of ProtonMail and ProtonVPN IP addresses. The block was no longer in place 4 days later. No explanation was given to ProtonMail for the block, nor for the block being lifted.[39]

On 29 January 2020, the Russian Federal Service for Supervision of Communications, Information Technology and Mass Media reported that it had implemented a complete block of ProtonMail services within Russia.[40] As a reason for the block, it cited ProtonMail's refusal to give up information relating to accounts that allegedly sent out spam with terror threats.[41][42] However, ProtonMail claimed that it did not receive any requests from Russian authorities regarding any such accounts.[43][44] In response to the block, the ProtonMail Twitter account recommended legitimate users circumvent the block via VPNs or Tor.

In March 2020, the company announced that even though the Russia ban was not particularly successful and the service continues to be largely available in Russia without utilising a VPN, ProtonMail will be releasing new anti-censorship features in both ProtonMail and ProtonVPN desktop and mobile apps which will allow more block attempts to be automatically circumvented.[45]

An email sent from one ProtonMail account to another is automatically encrypted with the public key of the recipient. Once encrypted, only the private key of the recipient can decrypt the email. When the recipient logs in, their mailbox password decrypts their private key and unlocks their inbox.

Emails sent from ProtonMail to non-ProtonMail email addresses may optionally be sent in plain text or with end-to-end encryption. With encryption, the email is encrypted with AES under a user-supplied password. The recipient receives a link to the ProtonMail website on which they can enter the password and read the decrypted email. ProtonMail assumes that the sender and the recipient have exchanged this password through a backchannel.[52] Such emails can be set to self-destruct after a period of time.[46]