Proton Mail Bridge connection issues with Thunderbird, Outlook, and Apple Mail

5 mins
Common issues and questions

In this article, we explain how Bridge secures its connection to your local email client and how to troubleshoot the most common errors.

Securing the Bridge to client connection 

Bridge sends your decrypted data to your chosen email client on a restricted communication channel that never leaves your device (via the loopback/localhost interface on 

Additionally, Bridge, by default, adds a layer of encryption (STARTTLS or SSL) to prevent unauthorized apps on your device from monitoring the local data that is exchanged. This is done using a self-signed TLS/SSL certificate that Bridge generates when you first set up the app. 

How to troubleshoot connection errors between your Client and Bridge

Sometimes the email client will fail to connect properly to Bridge, in which case Bridge will show a warning message similar to “Bridge failed to connect to your email client”. 

In this case, we recommend you begin troubleshooting by first trying the following three steps: 

  1. Remove any Proton accounts from your email client.
  2. Clear the cache inside Bridge.
  3. Retry the setup process.

1. Removing any Proton accounts from your email client

Outlook on Windows:

  1. Open Outlook.
  2. Open the File menu.
  3. Click on Account Settings, and select Account Settings in the dropdown menu. 
  4. In the new window, select your Proton Mail account and click Remove.

Screenshot of Outlook in Windows.
Screenshot of Account Settings in Outlook for Windows.

Outlook for macOS:

  1. Open Outlook.
  2. Inside the top menu bar, select Tools, and then select Accounts
  3. In the new window, select your Proton Mail account and click on the “ ” button in the lower left corner.

Screenshot of Accounts in Outlook for macOS.

Apple Mail

  1. Open the macOS System Settings, search for Profiles, and select Install, view, or remove configuration profiles.
  2. Select the account you wish to remove and click. Confirm yout choice when asked.


1. Open Thunderbird.

2. Click the Menu icon at the top-right -> Account Settings (or click Account Settings directly).

3. In the new window, select your Proton Mail account, click on the Account Actions button and select Remove account.

Screenshot of Account Settings in Thunderbird.

4. Make sure the “Remove account information” and “Remove message data” fields are checked. Click Remove.

Screenshot of Removing Account and Data in Thunderbird.

2. Delete your account from the Bridge to reset the message cache

1. Open Proton Mail Bridge.

2. Select your account from the left side.

3. Click the Trash icon to remove it from the Bridge.

4. Once the account is removed, you’ll need to log in again.

3. Retry the setup process

Follow one of our easy step-by-step guides(new window) to successfully complete your setup. 

Still encountering problems setting up your email client with Bridge? Contact our Support team(new window) or check out some of the relevant articles below.

Relevant articles 

Invalid password while setting up email client(new window)
Port already occupied error (Proton Mail Bridge)(new window)
Adding multiple accounts to Proton Mail Bridge(new window)

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