ProtonMail
ProtonMail is an end-to-end encrypted email service founded in 2013 in Geneva, Switzerland, by scientists who spent time at the CERN research facility. ProtonMail uses client-side encryption to protect email content and user data before they are sent to ProtonMail servers, unlike other common email providers such as Gmail and Outlook.com. The service can be accessed through a webmail client, the Tor network, or dedicated iOS and Android apps.

ProtonMail is run by its parent company Proton Technologies AG, which is based in the Canton of Geneva. The company also operates ProtonVPN, a VPN service. ProtonMail received initial funding through a crowdfunding campaign. Although the default account setup is free, the service is sustained by optional paid services. Initially invitation-only, ProtonMail opened up to the public in March 2016. In 2017, ProtonMail had over  users, and grew to over 5 million by September 2018, 20 million by the end of 2019, and over 50 million in 2020.

History

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

On 18 March 2015, ProtonMail received  from Charles River Ventures and the Fondation Genevoise pour l'Innovation Technologique (Fongit). 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.

On 19 January 2017, ProtonMail announced support through Tor, at the hidden service address protonirockerxow.onion. 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. 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.

On 25 July 2018, ProtonMail introduced address verification and Pretty Good Privacy (PGP) support, making ProtonMail interoperable with other PGP clients. In December 2019, ProtonMail launched "ProtonCalendar", a fully encrypted calendar.

The source code for the back-end remains closed source. However, ProtonMail released the source code for the web interface under an open-source license. ProtonMail also open sourced their mobile clients for iOS and Android, as well the ProtonMail Bridge app. 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.

DDoS attacks 
From 3 to 7 November 2015, ProtonMail was under several DDoS attacks that made the service largely unavailable to users. 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".

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. 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.

Block in China 
On 22 April 2020, ProtonMail confirmed on its ProtonVPN Twitter that ProtonMail and ProtonVPN are banned in China because it doesn't allow the government to spy.

Block in Belarus 
On 15 November 2019, Proton confirmed that government of the Republic of Belarus had issued a block across the country of ProtonMail and ProtonVPN IP addresses. The block was no longer in place four days later. No explanation was given to ProtonMail for the block, nor for the block being lifted.

Block in Russia 
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 the Russian Federation. 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. However, ProtonMail claimed that it did not receive any requests from Russian authorities regarding any such accounts. 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.

Compliance with Swiss court orders and IP Logging 
On 5 September 2021, ProtonMail confirmed it was forced to hand over IP addresses of French activists charged with theft and destruction of property after receiving a legally binding Swiss court order. Since article 271 of the Swiss Criminal Code prohibits Swiss companies from giving data to foreign authorities, French authorities asked the Swiss government for assistance. A similar request for assistance was made by the US government to the Swiss government in an August 2021 case involving death threats made against well-known immunologist Anthony Fauci. In that case however, ProtonMail was only able to provide a date of account creation.

On 6 September 2021, ProtonMail clarified its privacy policy to state "If you are breaking Swiss law, ProtonMail can be legally compelled to log your IP address as part of a Swiss criminal investigation" later. For this reason, the company strongly suggests that users who need to hide their identity from the Swiss government use their Tor hidden service/onion site. The company also clarified in its official statement that it cannot be forced by law to compromise its encryption. According to ProtonMail's transparency report, it is legally obligated to follow Swiss court orders, and in 2020, ProtonMail received 3,572 orders from Swiss authorities and contested 750 of them.

Encryption 

ProtonMail uses a combination of public-key cryptography and symmetric encryption protocols to offer end-to-end encryption. When a user creates a ProtonMail account, their browser generates a pair of public and private RSA keys:
 The public key is used to encrypt the user's emails and other user data.
 The private key capable of decrypting the user's data is symmetrically encrypted with the user's mailbox password.

This symmetrical encryption happens in the user's web browser using AES-256. Upon account registration, the user is asked to provide a login password for their account.

A lost login password can be recovered by sending an e-mail to ProtonMail Support. Two of the questions that are asked, in order for Support to provide renewed access to the account are:
 Do you remember to which addresses you have sent your last messages?
 Do you remember the email subjects from the last sent messages?

This implies that these data are readable by support agents and hence by data analysis services. They constitute meta-data, so that networks of communicating accounts along with subject headers can be charted.

ProtonMail also offers users an option to log in with a two-password mode which requires a login password and a mailbox password.
 The login password is used for authentication.
 The mailbox password encrypts the user's mailbox that contains received emails, contacts, and user information as well as a private encryption key.

Upon logging in, the user has to provide both passwords. This is to access the account and the encrypted mailbox and its private encryption key. The decryption takes place client-side either in a web browser or in one of the apps. The public key and the encrypted private key are both stored on ProtonMail servers. Thus ProtonMail stores decryption keys only in their encrypted form so ProtonMail developers are unable to retrieve user emails or reset user mailbox passwords. This system absolves ProtonMail from:
 Storing either the unencrypted data or the mailbox password.
 Divulging the contents of past emails but not future emails.
 Decrypting the mailbox if requested or compelled by a court order.

ProtonMail exclusively supports HTTPS and uses TLS with ephemeral key exchange to encrypt all Internet traffic between users and ProtonMail servers. Their 4096-bit RSA SSL certificate is signed by QuoVadis Trustlink Schweiz AG and supports Extended Validation, Certificate Transparency, Public Key Pinning, and Strict Transport Security. Protonmail.com holds an "A+" rating from Qualys SSL Labs.

In September 2015, ProtonMail added native support to their web interface and mobile app for PGP. This allows a user to export their ProtonMail PGP-encoded public key to others outside of ProtonMail, enabling them to use the key for email encryption. The ProtonMail team plans to support PGP encryption from ProtonMail to outside users.

A drawback of keeping the mail bodies encrypted is that the ProtonMail servers cannot search within them while they can search for their metadata.
The problems gets worse as the mail archives get larger and users have difficulties narrowing down their search targets.
A workaround is using ProtonMail Bridge to download and decrypt the messages and search for them locally.

Email sending 

An email message 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 message. When the recipient logs in, their mailbox password decrypts their private key and unlocks their inbox.

Email messages sent from ProtonMail to non-ProtonMail email addresses may optionally be sent in plain text or with end-to-end encryption. With encryption, the message 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 message. ProtonMail assumes that the sender and the recipient have exchanged this password through a backchannel. Such email messages can be set to self-destruct after a period of time.

Location and security 

Both ProtonMail and ProtonVPN are located in Switzerland to avoid any surveillance or information requests from countries under the Fourteen Eyes, and/or under government surveillance laws like the United States' Patriot Act or outside the bounds of law.

The company claims that it is also located in Switzerland because of its strict privacy laws.

In 2018 Nadim Kobeissi published an article arguing that as ProtonMail was generally accessed through a web client, "no end-to-end encryption guarantees have ever been provided by the ProtonMail service."

In 2020–2021, climate activists were arrested in France, after ProtonMail recorded and transmitted IP addresses to the authorities (upon request from French Police via Europol to the Swiss Federal Department of Justice and Police).

Data portability 
ProtonMail limits data portability by locking support for external email client software through IMAP and POP3 protocols behind a paywall. As of 2021, users are unable to back up their email account locally without paying.

Data centres 
ProtonMail maintains and owns its own server hardware and network in order to avoid utilizing a third party. It maintains two data centres, one in Lausanne and another in Attinghausen (in the former K7 military bunker under  of granite) as a backup. Since the servers are located in Switzerland, they are legally outside of the jurisdiction of the European Union, United States, and other countries. Under Swiss law, all surveillance requests from foreign countries must go through a Swiss court and are subject to international treaties. Prospective surveillance targets are promptly notified and can appeal the request in court.

Each data centre uses load balancing across web, mail, and SQL servers, redundant power supply, hard drives with full disk encryption, and exclusive use of Linux and other open-source software. In December 2014, ProtonMail joined the RIPE NCC in an effort to have more direct control over the surrounding Internet infrastructure.

Two-factor authentication 

ProtonMail currently supports two-factor authentication with TOTP tokens for its login process. As of October 2019, according to the official ProtonMail blog, U2F support for YubiKey and FIDO physical security keys is currently under development and will be available soon after the release of v4.0.

Account types 
, ProtonMail offers the following plans:

See also 
 Comparison of mail servers
 Comparison of webmail providers

References

External links 

 
 

Free software webmail
Internet properties established in 2013
Cross-platform software
Software using the MIT license
Software using the GPL license
Free security software
Cryptographic software
Secure communication
Internet privacy software
Swiss brands
Tor onion services