all-in-one privacy solution":["Proton Unlimited is een all-in-one privacy-oplossing"],"Black Friday":["Black Friday"],"No ads. Privacy by default.":["Geen advertenties. Standaard privacy."],"People before profits":["Mensen vóór winst"],"Security through transparency":["Veiligheid door openheid"],"The best Proton Mail ${ BLACK_FRIDAY } deals":["De beste ${ BLACK_FRIDAY }-deals voor Proton Mail"],"The world’s only community- supported email service":["'s Werelds enige door de community ondersteunde e-mailservice"]},"specialoffer:limited":{"${ hours } hour":["${ hours } uur","${ hours } uur"],"${ hoursLeft }, ${ minutesLeft } and ${ secondsLeft } left":["Nog ${ hoursLeft }, ${ minutesLeft } en ${ secondsLeft } resterend"],"${ minutes } minute":["${ minutes } minuut","${ minutes } minuten"],"${ seconds } second":["${ seconds } seconde","${ seconds } seconden"],"Limited time offer":["Aanbieding beperkt geldig"]},"specialoffer:listitem":{"Create multiple addresses":["Maak meerdere e-mailadressen aan"],"Hide-my-email aliases":["Hide-my-email-aliassen"],"Quickly unsubscribe from newsletters":["Meld u eenvoudig af voor nieuwsbrieven"],"Use your own domain name":["Gebruik uw eigen domeinnaam"]},"specialoffer:logos":{"As featured in":["Zoals te lezen in"]},"specialoffer:metadescription":{"Get an encrypted email that protects your privacy":["Kies voor beveiligde e-mail die uw privacy beschermt"]},"specialoffer:metatitle":{"Proton Mail Black Friday Sale - Up to 40% off":["Proton Mail Black Friday Sale - Tot 40% korting"]},"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.":["Profiteer tijdens Black Friday van wel 40% korting op Proton Mail-abonnementen. Bekijk geweldige aanbiedingen voor onze veilige, end-to-end versleutelde e-mailabonnementen."]},"specialoffer:newmetatitle":{"Proton Mail Black Friday sale | Up to 40% off secure email":["Proton Mail Black Friday Sale | Tot 40% korting op veilige e-mail"]},"specialoffer:note":{"* Billed at ${ TOTAL_SUM } for the first year":["*U betaalt ${ TOTAL_SUM } voor het eerste jaar"],"*Billed at ${ TOTAL_SUM } for the first 2 years":["*U betaalt ${ TOTAL_SUM } voor de eerste 2 jaar"],"30-day money-back guarantee":["30 dagen niet-goed-geld-terug-garantie"],"Billed at ${ TOTAL_SUM } for the first 2 years":["U betaalt ${ TOTAL_SUM } voor de eerste 2 jaar"],"Billed at ${ TOTAL_SUM } for the first year":["U betaalt ${ TOTAL_SUM } voor het eerste jaar"],"You save ${ SAVE_SUM }":["U bespaart ${ SAVE_SUM }"]},"specialoffer:off":{"${ DISCOUNT } off":["−${ DISCOUNT }"],"${ PERCENT_OFF } off":["−${ PERCENT_OFF }"]},"specialoffer:testimonial":{"I love my ProtonMail":["Ik ben fan van ProtonMail"],"My favorite email service":["Mijn favoriete e-mailservice"],"Thanks Proton for keeping us all safe in the complicated internet universe.":["Proton houdt ons allemaal veilig in het complexe internetuniversum."],"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":["Je krijgt waarvoor je betaalt. In het geval van Big Tech betekent 'gratis' dat je wordt gebruikt. Ik ben gestopt met Gmail en overgestapt op @ProtonMail"]},"specialoffer:time":{"Days":["Dagen"],"Hours":["Uur"],"Min":["Min"]},"specialoffer:title":{"And much more":["En nog veel meer"],"Make your inbox yours":["Personaliseer uw inbox"],"Safe from trackers":["Beschermd tegen trackers"],"Stay organized":["Houd overzicht"],"Black Friday email deals":["Black Friday-deals voor e-mail"],"Don’t just take our word for it":["U hoeft ons niet te geloven"],"Our story":["Ons verhaal"],"Transfer your data from Google in one click":["Zet uw gegevens van Google over met één klik"]},"specialoffer:tooltip":{"Access blocked content and browse privately. Includes ${ TOTAL_SERVERS }+ servers in ${ TOTAL_COUNTRIES }+ countries, connect up to 10 devices, access worldwide streaming services, malware and ad-blocker, and more.":["Bekijk geblokkeerde inhoud en surf privé. Met ${ TOTAL_SERVERS } servers in meer dan ${ TOTAL_COUNTRIES } landen, verbinding met maximaal 10 apparaten, wereldwijd toegang tot streamingdiensten, malware- en advertentieblokkering, en meer."],"Easily share your calendar with your family, friends or colleagues, and view external calendars.":["Deel uw agenda eenvoudig met uw familie, vrienden of collega's, en bekijk externe agenda's."],"Includes support for 1 custom email domain, 10 email addresses, 10 hide-my-email aliases, calendar sharing, and more.":["Ondersteuning voor 1 aangepast e-maildomein, 10 e-mailadressen, 10 hide-my-email-aliassen, gedeelde agenda's en meer."],"Includes support for 3 custom email domains, 15 email addresses, unlimited hide-my-email aliases, calendar sharing, and more.":["Ondersteuning voor 3 aangepaste e-maildomeinen, 15 e-mailadressen, onbeperkt hide-my-email-aliassen, gedeelde agenda's en meer."],"Manage up to 25 calendars, mobile apps, secured with end-to-end encryption, 1-click calendar import from Google, and more.":["Beheer tot 25 agenda's, mobiele apps, beveiligd met end-to-end versleuteling, agenda's van Google importeren met 1 klik, en meer."]},"Status Banner":{"At the moment we are experiencing issues with the Proton VPN service":["Momenteel werkt de dienst van Proton VPN niet naar behoren"],"Learn more":["Meer informatie"]},"Status banner":{"Learn more":["Meer informatie"],"Please note that at the moment we are experiencing issues with the ${ issues[0] } service.":["We ondervinden op dit moment problemen met de ${ issues[0] }service."],"We are experiencing issues with one or more services at the moment.":["We ondervinden momenteel problemen met een of meer services."]},"suggestions":{"Suggestions":["Suggesties"]},"Support":{"Sub category":["Subcategorie","Subcategorieën"]},"Support article":{"${ readingTime } min":["${ readingTime } min","${ readingTime } min"],"Category":["Categorie","Categorieën"],"Didn’t find what you were looking for?":["Niet gevonden wat u zocht?"],"General contact":["Algemene contactgegevens"],"Get help":["Krijg hulp"],"Legal contact":["Contactgegevens voor juridische zaken"],"Media contact":["Contactgegevens voor media"],"Partnerships contact":["Contactgegevens voor partnerschappen"],"Reading":["Lezen"]},"Support categories":{"Browse Proton product support":["Zoeken in Proton-productondersteuning"]},"Support category":{"There is no article in this category yet.":["Er zijn nog geen artikelen in deze categorie."]},"Support troubleshooting":{"--- Select ---":["--- Selecteren ---"],"Adding and importing contacts":["Contactpersonen toevoegen en importeren"],"App version":["App-versie"],"Automatically save contacts":["Contactpersonen automatisch opslaan"],"Bridge connection issues with Outlook, Apple Mail or Thunderbird":["Verbindingsproblemen Bridge met Outlook, Apple Mail of Thunderbird"],"Browser":["Browser"],"Check if this helps":["Kijk of dit helpt"],"Choose a category for your question":["Kies een categorie voor uw vraag"],"Connectivity errors on Android and iOS":["Verbindingsfouten op Android en iOS"],"Contacts":["Contactpersonen"],"Custom domain":["Aangepast domein"],"Desktop notifications":["Desktopmeldingen"],"Did this solve your issue ?":["Heeft dit uw probleem opgelost?"],"Difference between Combined Addresses Mode and Split Addresses Mode":["Verschil tussen de modus Gecombineerde adressen en de modus Gesplitste adressen"],"Differences between addresses, aliases, and sub-users":["Verschillen tussen adressen, aliassen en sub-gebruikers"],"Email notifications":["E-mailmeldingen"],"Email tracking protection":["E-mailbescherming tegen tracking"],"Encryption":["Versleuteling"],"Encryption keys management":["Versleutelingscodes beheren"],"Faster assistance is just a few clicks away — please make your selections":["Snellere ondersteuning binnen een paar klikken — maak uw keuze"],"How to avoid receiving spam messages":["Spamberichten ontvangen voorkomen"],"How to block unwanted email":["Ongewenste e-mails blokkeren"],"How to configure your email client for Bridge":["E-mailclient voor Bridge instellen"],"How to create contact groups":["Groepen voor contactpersonen aanmaken"],"How to create or edit CSV contacts":["CVS-contactgegevens aanmaken of aanpassen"],"How to install Proton Mail Bridge":["Proton Mail Bridge installeren"],"How to merge duplicate contacts":["Duplicaten van contactpersonen samenvoegen"],"How to send encrypted messages to external users":["Versleutelde berichten verzenden naar externe gebruikers"],"How to set up a custom domain":["Aanmaken aangepast domein"],"How to unsubscribe from Apple’s TestFlight notification emails":["Hoe u zich afmeldt voor de TestFlight notificatie e-mails van Apple"],"How to use auto-reply":["Automatisch antwoord gebruiken"],"How to use filters":["Filters gebruiken"],"How to use folders and labels":["Gebruikmaken van mappen en labels"],"How to use PGP encryption":["PGP-versleuteling gebruiken"],"Invalid password error while setting email client for Bridge":["Ongeldig wachtwoord bij instellen e-mailclient voor Bridge"],"Login security notification alerts":["Beveiligingswaarschuwingen bij inloggen"],"Manage mailbox appearance":["Mailboxweergave beheren"],"Mobile connectivity and synchronization":["Mobiele verbinding en synchronisatie"],"No, contact support":["Nee, contact opnemen met ondersteuning"],"Notifications":["Meldingen"],"Other":["Overig"],"Problems with deleting messages":["Probleemoplossing voor verwijderde berichten"],"Problems with moving messages":["Probleemoplossing voor verplaatsen berichten"],"Problems with read/unread message status":["Probleemoplossing met berichtstatus gelezen/ongelezen"],"Proton Mail Bridge":["Proton Mail Bridge"],"Proton Mail settings":["Proton Mail-instellingen"],"Push notifications not arriving":["Pushmeldingen komen niet aan"],"Sending and receiving messages":["Berichten verzenden en ontvangen"],"Sending and receiving messages limitations":["Limitaties op berichten verzenden en ontvangen"],"Sending and receiving troubleshooting":["Probleemoplossing verzenden en ontvangen"],"Spam filtering, Allow and Block lists":["Spam filteren, geaccepteerde en blokkeringslijsten"],"Sub-users and organizations":["Sub-gebruikers en organisaties"],"Thank you for your feedback":["Bedankt voor uw feedback"],"Troubleshooting":["Probleemoplossing"],"Verify custom domain records & anti-spoofing":["Verifieer aangepaste domeingegevens en anti-spoofing"],"What can we help with ?":["Waar mogen we u bij helpen?"],"What if your domain records fail (TXT, MX, SPF, DKIM, DMARC)":["Problemen met mislukte domeinrecords oplossen (TXT, MX, SPF, DKIM, DMARC)"],"What is encrypted on Proton Mail":["Wat is versleuteld bij Proton Mail"],"Yes":["Ja"]},"support_modal_search_query":{"How to use a custom domain?":["Gebruik van een aangepast domein"],"Search query":["Zoekopdracht"]},"support_modal_search_result":{"Search result":["Zoekresultaat"]},"support_modal_title":{"Blog search":["Blogs zoeken"],"Support search":["Ondersteuning zoeken"]},"support_search_button":{"Search":["Zoeken"]},"support_search_i_am_looking_for":{"I'm looking for":["Ik ben op zoek naar"]},"SupportForm":{"For a faster resolution, please report the issue from the Bridge app: Help > Report a problem.":["Om problemen sneller op te lossen, meldt u het via de Bridge-app: Help > Een probleem melden."],"Information":["Informatie"]},"SupportForm:option":{"Account Security":["Accountbeveiliging"],"Contacts":["Contactpersonen"],"Custom email domain":["Aangepast e-maildomein"],"Email delivery and Spam":["E-maillevering en spam"],"Encryption":["Versleuteling"],"Login and password":["Inlognaam en wachtwoord"],"Merge aliases and accounts":["Aliassen en accounts samenvoegen"],"Migrate to Proton":["Migreren naar Proton"],"Notifications":["Meldingen"],"Other":["Overig"],"Plans and billing":["Abonnementen en facturering"],"Proton for Business":["Proton for Business"],"Sign up":["Inschrijven"],"Storage":["Opslag"],"Users, addresses, and identities":["Gebruikers, adressen en identiteiten"]},"SupportForm:optionIntro":{"Select a topic":["Kies een onderwerp"]},"swiss_baseed_feature":{"Swiss based":["Gevestigd in Zwitserland"]},"Testimonial":{"Awards":["Awards"],"Customers":["Klanten"],"Featured":["Featured"],"Go to testimonial source":["Naar bron van testimonial"],"Reviews":["Reviews"],"Videos":["Video's"]},"Text":{"Find the plan that's right for you":["Vind het abonnement dat bij u past"],"If you need help, check out our ${ supportLink }.":["Bekijk onze ${ supportLink } als u hulp nodig hebt."],"The page you’re looking for might have been removed, or it could be an\nold link.":["De pagina waarnaar u op zoek bent, is mogelijk verwijderd, of u gebruikt een oude koppeling."]},"Title":{"On this page":["Op deze pagina"],"Related articles":["Gerelateerde artikelen"],"Share ${ thisPage }":["${ thisPage } delen"],"Thank you!":["Bedankt!"],"this page":["deze pagina"]},"Tooltip":{"More information":["Meer informatie"]},"tooltip_calendar":{"Create up to 20 custom & shareable encrypted calendars. On top of that, add up to 5 calendars from friends, family, colleagues, and organizations.":["Maak tot 20 aangepaste en deelbare versleutelde agenda's aan. Voeg daar bovenop tot 5 agenda's toe van vrienden, familie, collega's en organisaties."]},"tooltip_vpn":{"Access blocked content and browse privately. Includes ${ TOTAL_SERVERS }+ servers in ${ TOTAL_COUNTRIES }+ countries, highest VPN speed, ${ TOTAL_VPN_CONNECTIONS } VPN connections, worldwide streaming services, malware and ad-blocker, and more.":["Bekijk geblokkeerde inhoud en surf privé. Met meer dan ${ TOTAL_SERVERS } servers in meer dan ${ TOTAL_COUNTRIES } landen, de hoogste VPN-snelheid, ${ TOTAL_VPN_CONNECTIONS } VPN-verbindingen, wereldwijde streamingdiensten, malware- en advertentieblokkering, en meer."],"Access blocked content and browse privately. Includes ${ TOTAL_SERVERS }+ servers in ${ TOTAL_COUNTRIES }+ countries, highest VPN speed, 10 VPN connections, worldwide streaming services, malware and ad-blocker, and more.":["Bekijk geblokkeerde inhoud en surf privé. Met meer dan ${ TOTAL_SERVERS } servers in meer dan ${ TOTAL_COUNTRIES } landen, de hoogste VPN-snelheid, 10 VPN-verbindingen, wereldwijde streamingdiensten, malware- en advertentieblokkering, en meer."]},"version_history_label":{"Version history":["Versiegeschiedenis"]},"version_history_tooltip":{"Store up to ${ versionHistoryNumber } versions of each file for up to ${ years } years":["Bewaar tot ${ versionHistoryNumber } versies van elk bestand tot wel ${ years } jaar"]},"VideoModal":{"Get started in 2 minutes":["In 2 minuten aan de slag"]},"videosButtonLabel":{"Get started with videos":["Aan de slag met video's"]},"vpn_features_link":{"View VPN plans":["VPN-abonnementen bekijken"]},"vpn_features_useCase":{"Access blocked content and browse privately":["Bekijk geblokkeerde inhoud en surf privé"]}}},"unleashApi":"https://account.proton.me/api"};
// We need to import data (the framework context) from the server
// This Astro feature with define:vars works well but creates an inline script
// So we can't directly import the initFramework helper, we have to store the context
window.frameworkContext = frameworkContext;
})();
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(new window).
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(new window). 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(new window) 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(new window) and macOS(new window) 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(new window) 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(new window). Thank you for your support.
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