Proton Mail

Key takeaways

Proton Mail belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Proton Mail to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Proton Mail from memory before moving on to harder problems.

Reference excerpt

Proton Mail is an end-to-end encrypted email hosting service. It was launched in 2014 by Andy Yen, Jason Stockman and Wei Sun. Proton Mail is headquartered in Geneva, Switzerland. It is owned by the non-profit Proton Foundation through its subsidiary Proton AG, which also operates Proton VPN, Proton Drive, Proton Calendar, Proton Pass, Proton Wallet, Proton Meet, and Lumo AI. Proton Mail uses client-side encryption to protect email content and user data before they are sent to company servers, unlike other common email providers such as Gmail and Outlook.com. Proton Mail received its initial funding through a crowdfunding campaign, and initial access was by invitation only, but it opened to the public in 2016. There were two million users by 2017, almost 70 million by 2022, and 100 million users in 2024. The source code for the back end of Proton Mail remains closed-source, but Proton Mail released the source code for the web interface, iOS and Android apps, and the Proton Mail Bridge app under an open-source licence.

History On 16 May 2014, Proton Mail entered into public beta. Due to high demand, after three days beta signups were temporarily restricted to expand server capacity. Afterwards, Proton Mail implemented an invite-only waiting list. In summer 2014, Proton Mail received US$550,377 from 10,576 donors through a crowdfunding campaign on Indiegogo, while aiming for US$100,000. During the campaign, PayPal froze Proton Mail'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. The restrictions were lifted the following day. On 14 August 2015, Proton Mail released major version 2.0, which included a rewritten codebase for its web interface. On 17 March 2016, Proton Mail released major version 3.0, which saw the official launch of Proton Mail out of beta. With a new interface for the web client, version 3.0 also included the public launch of Proton Mail's iOS and Android beta applications and the removal of the waiting list. On 19 January 2017, Proton Mail announced a Tor onion site. On 21 November 2017, Proton Mail introduced Proton Mail Contacts, a zero-access encryption contacts manager. Proton Mail Contacts also utilizes digital signatures to verify the integrity of contacts data. On 6 December 2017, Proton Mail launched Proton Mail 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, Proton Mail introduced address verification and Pretty Good Privacy (specifically the open-source OpenPGP variant) support, making Proton Mail interoperable with other GPG clients. Around July 2021, Proton Mail's security and cryptographic architecture were both independently audited by Securitum, a European security auditing company, who uncovered no major issues or security vulnerabilities, and the audit results were publicly published. In April 2022, Proton acquired SimpleLogin, a company based in Paris, France that provides email aliasing addresses. SimpleLogin functionality was subsequently integrated into Proton Mail, but the email masking service is also available independently to use with any email provider. That same month, Proton also announced that users would now be able to create @proton.me email addresses, to complement the @protonmail.com addresses that were previously the default choice. In May 2022, following a rebrand of Proton, a space was added to the official name of the service, transitioning from ProtonMail to Proton Mail. In February 2023 a new version of the Proton Mail Bridge was launched that was considered to be a major improvement. Proton Mail Bridge allows Proton Mail to be used with any third party email client on Windows, macOS, or Linux, without losing end-to-end encryption. In April 2024, Proton Mail launched a desktop app for Windows and macOS. A version for Linux is in beta. The desktop client is only available for users with a paying subscription, despite Proton AG's earlier comments that it would be "gradually be made available to all users, including free". The app also allows access to Proton Calendar. In July 2024, Proton released a private AI writing assistant for Proton Mail, called Scribe, for the mail composer to initiate new emails. This is only available on higher tiers beginning on the paid 'Duo' plan, not even available for subscribers of the individual 'Unlimited' plan.

Encryption Proton Mail uses a combination of public-key cryptography and symmetric encryption protocols to offer end-to-end encryption. When a user creates a Proton Mail 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. Proton Mail also offers users an option to log in with a two-password mode that 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 Proton Mail servers. Thus Proton Mail stores decryption keys only in their encrypted form so Proton Mail developers are unable to retrieve user emails or reset user mailbox passwords. This system absolves Proton Mail from:

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Proton Mail

Start with the simplest possible case. Write down what Proton Mail claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Proton Mail before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Proton Mail ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Proton Mail

In research: Proton Mail appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Proton Mail in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Proton Mail is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cross-platform software, Cryptographic software, End-to-end encryption, so understanding it makes those chapters shorter.
In everyday life: Look for Proton Mail outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Proton Mail in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Proton Mail means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Proton Mail out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Proton Mail in simple terms?

Proton Mail is an end-to-end encrypted email hosting service. It was launched in 2014 by Andy Yen, Jason Stockman and Wei Sun.

Why does Proton Mail matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Proton Mail?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Proton Mail.