ProtonMail Bridge

Copyright (c) 2020 Proton Technologies AG

This repository holds the ProtonMail Bridge application. For a detailed build information see BUILDS. For licensing information see COPYING. For contribution policy see CONTRIBUTING.

Description

ProtonMail Bridge for e-mail clients.

When launched, Bridge will initialize local IMAP/SMTP servers and render its GUI.

To configure an e-mail client, firstly log in using your ProtonMail credentials. Open your e-mail client and add a new account using the settings which are located in the Bridge GUI. The client will only be able to sync with your ProtonMail account when the Bridge is running, thus the option to start Bridge on startup is enabled by default.

When the main window is closed, Bridge will continue to run in the background.

More details on the public website.

Keychain

You need to have a keychain in order to run the ProtonMail Bridge. On Mac or Windows, Bridge uses native credential managers. On Linux, use Gnome keyring or pass.

Environment Variables

Bridge application

• BRIDGESTRICTMODE: tells bridge to turn on bbolt's "strict mode" which checks the database after every Commit. Set to 1 to enable.

Dev build or run

• BRIDGE_VERSION: set the bridge app version used during testing or building
• PROTONMAIL_ENV: when set to dev it is not using Sentry to report crashes
• VERBOSITY: set log level used during test time and by the makefile

Integration testing

• TEST_ENV: set which env to use (fake or live)
• TEST_ACCOUNTS: set JSON file with configured accounts
• TAGS: set build tags for tests
• FEATURES: set feature dir, file or scenario to test

Files

Database

The database stores metadata necessary for presenting messages and mailboxes to an email client:

• Linux: ~/.cache/protonmail/bridge/<cacheVersion>/mailbox-<userID>.db (unless XDG_CACHE_HOME is set, in which case that is used as your ~)
• macOS: ~/Library/Caches/protonmail/bridge/<cacheVersion>/mailbox-<userID>.db
• Windows: %LOCALAPPDATA%\protonmail\bridge\<cacheVersion>\mailbox-<userID>.db

Preferences

User preferences are stored in json at the following location:

• Linux: ~/.cache/protonmail/bridge/<cacheVersion>/prefs.json (unless XDG_CACHE_HOME is set, in which case that is used as your ~)
• macOS: ~/Library/Caches/protonmail/bridge/<cacheVersion>/prefs.json
• Windows: %LOCALAPPDATA%\protonmail\bridge\<cacheVersion>\prefs.json

IMAP Cache

The currently subscribed mailboxes are held in a json file:

• Linux: ~/.cache/protonmail/bridge/<cacheVersion>/user_info.json (unless XDG_CACHE_HOME is set, in which case that is used as your ~)
• macOS: ~/Library/Caches/protonmail/bridge/<cacheVersion>/user_info.json
• Windows: %LOCALAPPDATA%\protonmail\bridge\<cacheVersion>\user_info.json

Lock file

Bridge utilises an on-disk lock to ensure only one instance is run at once. The lock file is here:

• Linux: ~/.cache/protonmail/bridge/<cacheVersion>/bridge.lock (unless XDG_CACHE_HOME is set, in which case that is used as your ~)
• macOS: ~/Library/Caches/protonmail/bridge/<cacheVersion>/bridge.lock
• Windows: %LOCALAPPDATA%\protonmail\bridge\<cacheVersion>\bridge.lock

TLS Certificate and Key

When bridge first starts, it generates a unique TLS certificate and key file at the following locations:

• Linux: ~/.config/protonmail/bridge/{cert,key}.pem (unless XDG_CONFIG_HOME is set, in which case that is used as your ~/.config)
• macOS: ~/Library/ApplicationSupport/protonmail/bridge/{cert,key}.pem
• Windows: %APPDATA%\protonmail\bridge\{cert,key}.pem