all-in-one privacy solution":["Proton Unlimited jest kompleksowym rozwiązaniem zapewniającym prywatność"],"Black Friday":["Czarny Piątek"],"No ads. Privacy by default.":["Brak reklam. Prywatność w standardzie."],"People before profits":["Ludzie przed zyskiem"],"Security through transparency":["Bezpieczeństwo dzięki przejrzystości"],"The best Proton Mail ${ BLACK_FRIDAY } deals":["Najlepsze oferty Proton Mail ${ BLACK_FRIDAY }"],"The world’s only community- supported email service":["Jedyna na świecie usługa e-mail wspierana przez społeczność"]},"specialoffer:limited":{"${ hours } hour":["${ hours } godzina","${ hours } godziny","${ hours } godzin","${ hours } godziny"],"${ hoursLeft }, ${ minutesLeft } and ${ secondsLeft } left":["Pozostało: ${ hoursLeft }, ${ minutesLeft } i ${ secondsLeft }"],"${ minutes } minute":["${ minutes } minuta","${ minutes } minuty","${ minutes } minut","${ minutes } minuty"],"${ seconds } second":["${ seconds } sekunda","${ seconds } sekundy","${ seconds } sekund","${ seconds } sekundy"],"Limited time offer":["Oferta ograniczona czasowo"]},"specialoffer:listitem":{"Create multiple addresses":["Utwórz wiele adresów"],"Hide-my-email aliases":["Aliasy hide-my-email"],"Quickly unsubscribe from newsletters":["Szybko anuluj subskrypcję biuletynów"],"Use your own domain name":["Korzystaj z własnej nazwy domeny"]},"specialoffer:logos":{"As featured in":["Opinie naszych klientów"]},"specialoffer:metadescription":{"Get an encrypted email that protects your privacy":["Uzyskaj zaszyfrowaną usługę e-mail, która chroni Twoją prywatność"]},"specialoffer:metatitle":{"Proton Mail Black Friday Sale - Up to 40% off":["Wyprzedaż Proton Mail z okazji Czarnego Piątku – uzyskaj do 40% zniżki"]},"specialoffer:newmetadescription":{"Get up to 40% off Proton Mail subscriptions this Black Friday. Find great deals on our secure end-to-end encrypted email plans.":["Uzyskaj do 40% zniżki na subskrypcje Proton Mail w ten Czarny Piątek. Znajdź wspaniałe oferty naszych bezpiecznych planów usługi poczty elektronicznej w szyfrowaniu end-to-end."]},"specialoffer:newmetatitle":{"Proton Mail Black Friday sale | Up to 40% off secure email":["Wyprzedaż Proton Mail z okazji Czarnego Piątku | Do 40% zniżki na bezpieczną pocztę elektroniczną"]},"specialoffer:note":{"* Billed at ${ TOTAL_SUM } for the first year":["* Płatne ${ TOTAL_SUM } za pierwszy rok"],"*Billed at ${ TOTAL_SUM } for the first 2 years":["* Płatne ${ TOTAL_SUM } za pierwsze 2 lata"],"30-day money-back guarantee":["30-dniowa gwarancja zwrotu pieniędzy"],"Billed at ${ TOTAL_SUM } for the first 2 years":["Płatne ${ TOTAL_SUM } za pierwsze 2 lata"],"Billed at ${ TOTAL_SUM } for the first year":["Płatne ${ TOTAL_SUM } za pierwszy rok"],"You save ${ SAVE_SUM }":["Oszczędzasz ${ SAVE_SUM }"]},"specialoffer:off":{"${ PERCENT_OFF } off":["-${ PERCENT_OFF }"]},"specialoffer:testimonial":{"I love my ProtonMail":["Uwielbiam ProtonMail"],"My favorite email service":["Moja ulubiona usługa e-mail"],"Thanks Proton for keeping us all safe in the complicated internet universe.":["Dziękuję Protonowi za dbanie o nasze bezpieczeństwo w skomplikowanym internetowym uniwersum."],"You get what you pay for. In the case of big tech, if you pay nothing, you get used. I quit using Gmail and switched to @ProtonMail":["Dostajesz to, za co płacisz. W przypadku przedsiębiorstw big tech, jeśli nie płacisz nic, zostaniesz wykorzystany. Przestałam korzystać z Gmail i przeniosłam się na @ProtonMail"]},"specialoffer:time":{"Days":["Dni"],"Hours":["Godz."],"Min":["Min"]},"specialoffer:title":{"And much more":["I wiele więcej"],"Safe from trackers":["Żadnych elementów śledzących"],"Stay organized":["Dbaj o dobrą organizację"],"Black Friday email deals":["Oferty e-mailowe na Czarny Piątek"],"Don’t just take our word for it":["Nie musisz wierzyć nam na słowo"],"Make your inbox yours":["Niech skrzynka odbiorcza należy tylko do Ciebie"],"Our story":["Nasza historia"],"Transfer your data from Google in one click":["Przenieś dane z Google jednym kliknięciem"]},"specialoffer:tooltip":{"Access blocked content and browse privately. Includes ${ TOTAL_VPN_SERVERS }+ servers in ${ TOTAL_VPN_COUNTRIES }+ countries, connect up to 10 devices, access worldwide streaming services, malware and ad-blocker, and more.":["Uzyskaj dostęp do zablokowanych treści i przeglądaj prywatnie Internet. Obejmuje ponad ${ TOTAL_VPN_SERVERS } serwerów w ponad ${ TOTAL_VPN_COUNTRIES } krajach z możliwością połączenia do 10 urządzeń, a także dostęp do globalnych usług streamingu, blokadę reklam, złośliwego oprogramowania i wiele więcej."],"Easily share your calendar with your family, friends or colleagues, and view external calendars.":["Łatwo udostępniaj swój kalendarz rodzinie, znajomym oraz współpracownikom i wyświetla kalendarze zewnętrzne."],"Includes support for 1 custom email domain, 10 email addresses, 10 hide-my-email aliases, calendar sharing, and more.":["Zawiera obsługę 1 niestandardowej domeny e-mail, 10 adresów e-mail, 10 aliasów hide-my-email, udostępnianie kalendarza i nie tylko."],"Includes support for 3 custom email domains, 15 email addresses, unlimited hide-my-email aliases, calendar sharing, and more.":["Obejmuje obsługę 3 niestandardowych domen e-mail, 15 adresów e-mail, nielimitowane aliasy hide-my-email, udostępnianie kalendarza i nie tylko."],"Manage up to 25 calendars, mobile apps, secured with end-to-end encryption, 1-click calendar import from Google, and more.":["Zarządzanie nawet 25 kalendarzami, aplikacje mobilne, bezpieczne szyfrowanie metodą end-to-end, importowanie kalendarza za pomocą jednego kliknięcia z Google i więcej."]},"Status Banner":{"At the moment we are experiencing issues with the Proton VPN service":["W tej chwili mamy problemy z usługą Proton VPN"]},"Status banner":{"Learn more":["Dowiedz się więcej"],"Please note that at the moment we are experiencing issues with the ${ issues[0] } service.":["Uwaga: obecnie występują problemy z usługą ${ issues[0] }."],"We are experiencing issues with one or more services at the moment.":["Mamy problemy z co najmniej jedną usługą."]},"steps":{"Step":["Krok"]},"suggestions":{"Suggestions":["Sugestie"]},"Support":{"Sub category":["Podkategoria","Podkategorie","Podkategorii","Podkategorii"]},"Support article":{"${ readingTime } min":["${ readingTime } min","${ readingTime } min","${ readingTime } min","${ readingTime } min"],"Category":["Kategoria","Kategorie","Kategorii","Kategorii"],"Didn’t find what you were looking for?":["Nie znaleziono szukanej frazy?"],"General contact":["Skontaktuj się, wykorzystując ogólne zapytanie"],"Get help":["Uzyskaj pomoc"],"Legal contact":["Skontaktuj się z działem prawnym"],"Media contact":["Skontaktuj się z zespołem medialnym"],"Partnerships contact":["Skontaktuj się z zespołem ds. partnerstwa"],"Reading":["Odczytywanie"]},"Support Form Platform option":{"VPN for Android TV":["VPN dla Android TV"],"VPN for Apple TV":["VPN na Apple TV"],"VPN for Chromebook":["VPN dla Chromebooka"]},"Support troubleshooting":{"App version":["Wersja aplikacji"],"Browser":["Przeglądarka"],"Check if this helps":["Sprawdź, czy to pomoże"],"Choose a product":["Wybierz produkt"],"Did this solve your issue?":["Czy Twój problem został rozwiązany?"],"Faster assistance is just a few clicks away":["Szybsze wsparcie uzyskasz w kilka kliknięć"],"How can we help?":["Jak możemy pomóc?"],"No, contact support":["Nie, skontaktuj się z pomocą techniczną"],"Please fill out one field after another":["Wypełnij pola jedno po drugim"],"Please make your selections":["Dokonaj wyboru"],"Proton account":["Konto Proton"],"Proton for Business":["Proton for Business"],"Thank you for your feedback":["Dziękujemy za podzielenie się opinią"],"What can we help with?":["W czym możemy pomóc?"],"Yes":["Tak"]},"support_modal_search_query":{"Search query":["Zapytanie wyszukiwania"]},"support_search_button":{"Search":["Szukaj"]},"support_search_i_am_looking_for":{"I'm looking for":["Szukam"]},"SupportForm":{"For a faster resolution, please report the issue from the Bridge app: Help > Report a problem.":["W celu szybszego rozwiązania problemu dokonaj zgłoszenia przez aplikację Bridge: Pomoc > Zgłoś problem."],"Information":["Informacje"]},"SupportForm:option":{"Account Security":["Bezpieczeństwo konta"],"Contacts":["Kontakty"],"Custom email domain":["Niestandardowa domena e-mail"],"Email delivery and Spam":["Dostarczanie wiadomości e-mail i spam"],"Encryption":["Szyfrowanie"],"Login and password":["Login i hasło"],"Merge aliases and accounts":["Scalanie aliasów i kont"],"Migrate to Proton":["Migracja do Proton"],"Notifications":["Powiadomienia"],"Other":["Inne"],"Plans and billing":["Plany i rozliczenia"],"Proton for Business":["Proton for Business"],"Sign up":["Rejestracja"],"Storage":["Przestrzeń dyskowa"],"Users, addresses, and identities":["Użytkownicy, adresy i tożsamości"]},"SupportForm:optionIntro":{"Select a topic":["Wybierz temat"]},"Testimonial":{"Awards":["Nagrody"],"Customers":["Klienci"],"Featured":["Wyróżnione"],"Go to testimonial source":["Przejdź do źródła referencji"],"Open source of award":["Otwórz źródło nagrody"],"Open source of quote":["Otwórz źródło cytatu"],"Reviews":["Opinie"],"Videos":["Pliki wideo"],"Watch on TikTok":["Oglądaj na TikTok"],"Watch on YouTube":["Oglądaj na YouTube"]},"TestimonialCategory":{"Awards":["Nagrody"],"Customers":["Klienci"],"Featured":["Wyróżnione"],"Media":["Multimedia"],"Reviews":["Opinie"],"Videos":["Pliki wideo"]},"Text":{"If you need help, check out our ${ supportLink }.":["Jeśli potrzebujesz pomocy, sprawdź naszą ${ supportLink }."],"The page you’re looking for might have been removed, or it could be an\nold link.":["Strona, której szukasz, mogła zostać usunięta lub link jest przestarzały."],"Your question may already have an answer in our knowledge base:":["Na Twoje pytanie może już istnieć odpowiedź w bazie wiedzy:"]},"Title":{"On this page":["Na tej stronie"],"Page not found":["Nie znaleziono strony"],"Related articles":["Powiązane artykuły"],"Share ${ thisPage }":["Udostępnij ${ thisPage }"],"Switch to Proton Pass - Contact us":["Przejdź na Proton Pass – skontaktuj się z nami"],"Thank you!":["Dziękujemy!"],"this page":["tę stronę"]},"tooltip_vpn":{"Access blocked content and browse privately. Includes ${ TOTAL_VPN_SERVERS }+ servers in ${ TOTAL_VPN_COUNTRIES }+ countries, highest VPN speed, ${ TOTAL_VPN_CONNECTIONS } VPN connections, worldwide streaming services, malware and ad-blocker, and more.":["Uzyskaj dostęp do zablokowanych treści i przeglądaj prywatnie Internet. Obejmuje ponad ${ TOTAL_VPN_SERVERS } serwerów w ponad ${ TOTAL_VPN_COUNTRIES } krajach, najwyższe prędkości VPN, ${ TOTAL_VPN_CONNECTIONS } połączeń VPN, usługi streamingu na całym świecie, blokowanie reklam oraz złośliwego oprogramowania i wiele więcej."]},"vpn_servers":{"Get Proton VPN Plus":["Wybierz plan Proton VPN Plus"]},"wallet_signup_2024:Action":{"Get Proton Wallet":["Wybierz Proton Wallet"]},"wallet_signup_2024:Homepage hero product link title":{"Wallet":["Portfel"]},"wallet_signup_2024:Homepage product navigation bar":{"Wallet":["Portfel"]},"wallet_signup_2024:menu item":{"Bitcoin guide":["Przewodnik po systemie Bitcoin"],"Proton Wallet news":["Aktualności Proton Wallet"],"Proton Wallet support":["Wsparcie dla Proton Wallet"]},"wallet_signup_2024:Pricing":{"Includes everything in Proton Unlimited and":["Zawiera wszystko, co Proton Unlimited oraz"],"Limited availability":["Ograniczona dostępność"],"The easiest way to securely own, send, and receive Bitcoin":["Najprostszy sposób na bezpieczne przechowywanie, wysyłanie i odbieranie waluty Bitcoin"]},"wallet_signup_2024:ProductRange":{"Discover Proton Wallet":["Odkryj rozwiązanie Proton Wallet"],"Store and transact Bitcoin privately with an encrypted self-custody wallet.":["Bezpiecznie przechowuj i przesyłaj Bitcoiny dzięki szyfrowanemu portfelowi typu self-custody."]},"wallet_signup_2024:wallet bitcoin":{"Learn about Bitcoin, the Internet's value network.":["Dowiedz się więcej o internetowym systemie gotówkowym Bitcoin."]},"wallet_signup_2024:wallet overview":{"Ensure you're always in control of your Bitcoin.":["Miej pełny nadzór nad swoimi Bitcoinami."]},"wallet_signup_2024:wallet security":{"The encrypted, open-source wallet that puts you in control.":["Szyfrowany portfel o otwartym kodzie źródłowym, który daje Ci pełną kontrolę."]}}},"base":"blog","cdn":{"enabledForAssets":true,"enabledForImages":true,"url":"https://pmecdn.protonweb.com/"},"unleashApi":"https://account.proton.me/api"};
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Proton Mail Bridge is a desktop application that runs in the background on your computer and encrypts and decrypts your mail as it enters and leaves your device. It allows for full integration of your Proton Mail account with email clients like Microsoft Outlook, Mozilla Thunderbird, and Apple Mail.
This document discusses how Bridge handles sensitive information, describes its potential attack vectors, and explains the security features that mitigate these attacks. (Note: This security model applies to the Bridge application for Linux, macOS, and Windows.)
This security model is technical in nature, but was written in plain language so that the average user can understand the important takeaways. You can also read more about what Proton Mail is and is not designed to protect you from in the Proton Mail threat model(nowe okno).
As part of normal, day-to-day operations, Bridge must handle different types of data with varying levels of sensitivity. This data includes (but is not limited to):
User credentials and an access token for authentication with the Proton servers
Public and private keys for sending and reading messages
Encrypted messages, attachments, and metadata
We explain how Bridge secures this sensitive data in greater detail below.
Your passwords never leave your machine Users log in to Bridge, which in turn authenticates with the Proton Mail API using the Secure Remote Password protocol(nowe okno). This authentication process ensures a user’s password never leaves their machine, and it generates an access token and a refresh token.
The access token is relatively short-lived and is used to authenticate any subsequent API requests; it is stored in the device’s memory. The refresh token is used to generate new access tokens and is stored securely in the operating system’s keychain (Windows Credentials Manager, macOS Keychain, or pass/gnome-keyring on Linux). The user’s hashed and salted mailbox password (used to decrypt their PGP keys) and Bridge password (used to connect an email client to Bridge) are also held in the operating system’s keychain.
Ensuring a secure connection to Proton servers Bridge communicates with the Proton Mail API over an encrypted TLS connection. It additionally employs TLS certificate public key pinning to ensure it only connects to trusted Proton Mail servers. If Bridge receives an untrusted public key, it will assume an unknown intermediary is pretending to be a Proton server and immediately warn the user.
Bridge never stores or shares a user’s PGP keys After the user logs in, Bridge downloads their encrypted, private PGP keys from the Proton servers and unlocks them. These keys are held in the device’s memory, never on disk. Whenever a user turns off their device, they wipe its memory. This makes it unlikely an attacker will be able to obtain a copy of a user’s PGP keys, even if they steal the user’s device. These keys are also never shared with other applications on your device and stay within Bridge’s memory space.
Bridge does not store decrypted message data When an IMAP client requests a message body or attachment, it is downloaded from the Proton servers as an encrypted PGP message, decrypted locally, and then transmitted to the IMAP client. Similar to the user’s PGP keys, Bridge does not permanently store any message bodies or attachments to disk, further reducing the amount of sensitive data available on the device.
Attack mitigation
Here we describe the potential attack vectors of Bridge and how we mitigate these attacks.
Reducing the threat of a MITM attack
As described, Bridge employs TLS certificate pinning, which mitigates the risk of a network-level man-in-the-middle (MITM) attack.
Furthermore, the content of messages sent from Bridge to Proton Mail users or external recipients using PGP has an additional layer of protection thanks to end-to-end encryption. This means Bridge encrypts the user’s message before it leaves their device. The message remains encrypted until it reaches the recipient’s device, which decrypts it. This prevents any third party, including Proton Mail, from accessing the content of a user’s message. Messages sent this way remain inaccessible because a user’s mailbox password never leaves their device and, thus, is never transmitted to an attacker.
Secure updates
Bridge on Windows and macOS includes a feature that allows it to self-update. The update process has additional safeguards in place to verify that only trusted versions of Bridge that are created and signed by Proton Mail are installed.
Bridge recommended use cases
Bridge is a unique tool when compared to the other Proton Mail apps. As such, there are specific cases in which it would be more practical and useful than other Proton Mail apps.
Below are some examples of recommended use cases for Bridge:
Offline editing If you find yourself without a stable Internet connection, you can use your favorite email client with Bridge to download emails while you do have good Internet access and then process them offline later. Most email clients will automatically send and receive your drafts once you are back online.
Offline backups of your emails are required If you need to have offline copies of your messages for whatever reason, Bridge is the easiest way to accomplish this. The Bridge app enables your IMAP/SMTP client to do this automatically if you choose to do so.
Add Proton Mail security to already known email clients If you or your staff do not feel confident learning how to use a new email service, Bridge lets you add Proton Mail encryption to your messages while continuing to use your favorite IMAP/SMTP email client. These clients include Outlook, Thunderbird, and Apple Mail, all applications that many people are familiar with. This means that once you set up Bridge, using it does not require any new training.
Bridge security model scope
No application is 100% secure, and no piece of software can protect its user against every potential threat. Proton Mail Bridge is engineered to provide additional protection to its users’ data, but certain conditions are outside of the scope of the security model.
User device security We assume users run the Bridge app in a safe environment. For instance, we assume that Bridge program files are installed to a location where normal (non-admin) users have no write privileges. Furthermore, we expect the user’s device to be free of any malicious software (keyloggers, screen recorders, memory scanners, etc.) that could access the device’s data in memory or on disk. Bridge, unfortunately, cannot secure your data if your device is already compromised.
Additionally, we assume that the IMAP/SMTP ports that the email client connects to are not exposed beyond the device that Bridge is running on. The Bridge application ignores all connections that do not originate from the localhost, and we assume the user will not attempt to circumvent this.
Bridge installer security We assume that the user securely downloaded the Bridge installer from our server (the server should present a valid and expected SSL certificate). For Windows and macOS, the operating system inspects the signatures on the installer file automatically before installation. It then displays the results to the user, which we assume they properly verify. We recommend Linux users refer to our support article on Verifying the Proton Mail Bridge package(nowe okno) for instructions. If you download the Bridge application from an unauthorized source, we cannot guarantee the safety of the installer.
Our recommendations for keeping your device secure
We have invested heavily in the security of our Bridge app. You can help maximize the security of your own device by taking a few simple measures:
Encrypt your device’s hard drive. Windows(nowe okno) and macOS(nowe okno) devices all have built-in encryption systems, but you have to turn them on. Once you have encrypted your drive, write down your recovery code and store it in a secure place.
Enable your operating system’s antivirus protection, if available.
Ensure your network ports are secured by a firewall to prevent outside machines from connecting to them.
Do not install untrusted programs on your device. This includes unknown open source versions of Bridge. Downloading Bridge directly from Proton Mail(nowe okno) is the safest option.
Do not open links or download attachments from untrusted senders.
Conclusion
Our first priority is always our users’ security. Our goal is to make it easy for anyone to protect their privacy by creating tools that apply advanced cryptography to their messages automatically. The Bridge tool was designed to add additional security to already existing IMAP/SMTP email clients. By keeping your device secure, you can use these email clients and still take charge of your data. Thank you for your support!
Proton Mail and Proton VPN are funded by community contributions. If you would like to support our development efforts, you can upgrade to a paid plan(nowe okno). Thank you for your support.
Thousands of businesses of all sizes were impacted by cybercrime in 2024. Here
are the top cybersecurity threats we expect companies to face in 2025—and how
Proton Pass can protect your business.