Proton Mail Bridge is a desktop connector that lets paid Proton Mail users securely access encrypted mail through compatible IMAP and SMTP clients while encryption and decryption remain handled locally.
Proton Mail Bridge lets paid Proton Mail users connect encrypted accounts to desktop email clients that rely on IMAP and SMTP. Instead of exposing Proton’s encrypted mailbox directly to a conventional client, the application creates local mail servers on the computer and handles encryption or decryption between that client and Proton’s servers. Proton Mail Bridge works with supported clients such as Outlook and Thunderbird on Windows, allowing users to keep familiar desktop workflows while retaining Proton’s server-side privacy model. After signing in, users copy the mailbox credentials generated by Bridge into their email client. The application must keep running for new mail to synchronize and outgoing messages to be sent.
Proton Mail Bridge communicates with the email client only through local interfaces, while its connection to Proton services remains encrypted over the network. It generates separate mailbox credentials for the client, so users should not enter their normal Proton Account password into IMAP or SMTP settings. People who review setup instructions in Google can keep browser activity separate while Bridge manages local mailbox access and encryption. A local encrypted cache improves synchronization performance and can be moved from the default storage location through Bridge settings. Users can also choose between combined and split address modes when an account has multiple addresses, although switching modes may require reconfiguring those accounts inside the desktop mail client.
Proton Mail Bridge is most useful when a user wants Proton Mail privacy without giving up a mature desktop client’s offline storage, search, rules, extensions, or familiar interface. Incoming encrypted messages are retrieved from Proton and decrypted locally before the mail client accesses them through Bridge’s localhost IMAP server; outgoing messages travel through the local SMTP service, where Bridge applies the appropriate Proton encryption behavior before delivery. The local cache is encrypted by Bridge, but the connected email client may store downloaded messages unencrypted, so device and disk security still matter. Proton Mail Bridge uses the operating system credential store on Windows to protect sensitive local data and requires that credential mechanism to remain available. Version 3.25.0 is a security-focused stable release that also improves error reporting and fixes crash and update-cleanup issues. Proton recommends updating to version 3.25 or newer because of significant security improvements included in this release.
Proton Mail Bridge creates local IMAP and SMTP services that desktop email clients use instead of connecting directly to Proton’s encrypted mailbox servers. The local connection is restricted to the computer and protected with TLS by default. This design lets standard mail applications exchange messages while Bridge performs the encryption-related work they cannot handle themselves.
Each mailbox receives credentials generated specifically for the local Bridge connection rather than reusing the Proton Account password. Proton Mail Bridge displays the username, password, host, and port values required by the email client. If an account is removed and added again, users may need to update stored client credentials with the newly generated values.
Proton Mail Bridge stores synchronized message data in an encrypted local cache to improve reliability and communication with the connected email client. The cache location can be changed from Bridge settings when storage organization requires it. Encryption protects Bridge’s cached copy, although a separate email client may maintain its own locally stored messages under different security controls.
Accounts with multiple Proton addresses can use combined or split address modes. Combined mode places messages for the account’s addresses into shared mailbox folders, while split mode exposes addresses separately to the client. Proton Mail Bridge defaults to combined mode, and changing an already configured mailbox to split mode can require removing and re-adding accounts in the client.
Proton Mail Bridge is designed for desktop clients that support IMAP and SMTP. Proton officially tests several Outlook versions and Thunderbird on Windows, with additional supported clients on macOS and Linux. Other standards-compatible clients may work, but Proton warns that behavior can vary because different applications implement IMAP differently and unsupported clients receive more limited troubleshooting support.
Bridge can download and install updates automatically in the background, helping users stay on maintained releases without repeatedly fetching installers. Proton Mail Bridge also provides a manual update path if automatic updating does not complete. Version 3.25.0 includes significant security improvements, clearer errors, crash fixes, and cleanup for temporary files left by previous update operations.
The built-in Repair function can reload configured accounts, refresh cached data, and download mail again when synchronization problems or local conflicts appear. Proton Mail Bridge also exposes settings for moving the cache and adjusting local connection ports. These controls give users recovery options before resorting to a complete uninstall and manual removal of Bridge configuration data.
Proton Mail Bridge includes a command-line interface for users who prefer terminal-based management instead of the graphical window. Available commands cover Bridge and account operations documented by Proton, while the desktop application remains the normal path for guided setup. CLI access is useful on supported systems where administrators or advanced users want a more direct management workflow.
Proton Mail Bridge connects a paid Proton Mail account to compatible desktop email clients using local IMAP and SMTP services. It decrypts incoming mail locally for the client and handles outgoing messages before they are sent through Proton. This allows applications such as supported Outlook versions and Thunderbird to work with Proton Mail without connecting directly to the encrypted mailbox infrastructure.
No. Proton currently makes Bridge available only with paid plans that include Proton Mail. A user on the free plan must upgrade to an eligible paid subscription before signing in to the application. The exact plans and entitlements can change, so account eligibility should be checked in the current Proton plan information before installation or deployment.
No. Bridge provides local IMAP and SMTP services rather than POP3. IMAP handles synchronized mailbox access and SMTP handles outgoing mail, which allows a desktop client to work with Proton Mail while Bridge performs local encryption and decryption. Users who want local copies can download mail through their email client and use that client’s export or archival features.
The main window can be closed, but Proton Mail Bridge must continue running in the background for the connected email client to send and synchronize new messages. If the user signs out of the Proton account in Bridge or exits the application completely, the mail client cannot connect through its local IMAP and SMTP services until Bridge is running and authenticated again.
Bridge encrypts its own local message cache, and sensitive local data is protected using the operating system’s credential storage. However, the connected desktop email client may store downloaded messages locally in unencrypted form. Users handling sensitive mail should therefore protect the Windows account, maintain device security, and consider full-disk encryption rather than assuming every local copy is encrypted.
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