Copyright (c) 2026 Proton AG
This repository holds the Proton Mail Bridge application. For a detailed build information see BUILDS. The license can be found in LICENSE file, for more licensing information see COPYING_NOTES. For contribution policy see CONTRIBUTING.
Proton Mail Bridge for e-mail clients.
When launched, Bridge will initialize local IMAP/SMTP servers and render its GUI.
To configure an e-mail client, first log in using your Proton Mail 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 Proton Mail 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.
The launcher is a binary used to run the Proton Mail Bridge.
The Official distribution of the Proton Mail Bridge application contains both a launcher and the app itself. The launcher is installed in a protected area of the system (i.e. an area accessible only with admin privileges) and is used to run the app. The launcher ensures that nobody tampered with the app's files by verifying their signature using a hardcoded public key. App files are placed in regular userspace and are signed by Proton's private key. This feature enables the app to securely update itself automatically without asking the user for a password.
You need to have a keychain in order to run Proton Mail Bridge. On Mac or
Windows, Bridge uses native credential managers. On Linux, use secret-service freedesktop.org API
(e.g. Gnome keyring)
or
pass. We are working on allowing other secret
services (e.g. KeepassXC), but for now only gnome-keyring is usable without
major problems.
APP_VERSION: set the bridge app version used during testing or buildingPROTONMAIL_ENV: when set to dev it is not using Sentry to report crashesVERBOSITY: set log level used during test time and by the makefileTEST_ENV: set which env to use (fake or live)TEST_ACCOUNTS: set JSON file with configured accountsTAGS: set build tags for testsFEATURES: set feature dir, file or scenario to testThere are now three types of system folders which Bridge recognises:
| Windows | Mac | Linux | Linux (XDG) | |
|---|---|---|---|---|
| config | %APPDATA%\protonmail\bridge-v3 | ~/Library/Application Support/protonmail/bridge-v3 | ~/.config/protonmail/bridge-v3 | $XDG_CONFIG_HOME/protonmail/bridge-v3 |
| cache | %LOCALAPPDATA%\protonmail\bridge-v3 | ~/Library/Caches/protonmail/bridge-v3 | ~/.cache/protonmail/bridge-v3 | $XDG_CACHE_HOME/protonmail/bridge-v3 |
| data | %APPDATA%\protonmail\bridge-v3 | ~/Library/Application Support/protonmail/bridge-v3 | ~/.local/share/protonmail/bridge-v3 | $XDG_DATA_HOME/protonmail/bridge-v3 |
| temp | %LOCALAPPDATA%\Temp | $TMPDIR if non-empty, else /tmp | $TMPDIR if non-empty, else /tmp | $TMPDIR if non-empty, else /tmp |
| Base Dir | Path | |
|---|---|---|
| bridge lock file | cache | bridge.lock |
| bridge-gui lock file | cache | bridge-gui.lock |
| vault | config | vault.enc |
| gRPC server json | config | grpcServerConfig.json |
| gRPC client json | config | grpcClientConfig_.json |
| gRPC Focus server json | config | grpcFocusServerConfig.json |
| Logs | data | logs |
| gluon DB | data | gluon/backend/db |
| gluon messages | data | gluon/backend/store |
| Update files | data | updates |
| sentry cache | data | sentry_cache |
| Mac/Linux File Socket | temp | bridge{4_DIGITS} |
$ claude mcp add proton-bridge \
-- python -m otcore.mcp_server <graph>