Bridge connection issues with Thunderbird, Outlook & Apple Mail

NOTE: Thunderbird 78.3.X doesn’t allow adding self-signed SMTP certificates. This causes an error when sending messages via Bridge. To work around this issue, temporarily set the SSL field to None instead of STARTTLS when setting up your account on Thunderbird.

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

Securing Proton 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 127.0.0.1). 

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 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 ProtonMail 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 ProtonMail account and click on the “ ” button in the lower left corner.

Screenshot of Accounts in Outlook for macOS.

Apple Mail

  1. Open Apple Mail.
  2. In the toolbar, select Mail and then click Accounts… 
  3. In the new window, select your ProtonMail account and remove it by clicking on the “” button in the lower left corner.

Screenshot of Apple Mail.
Screenshot of Internet Accounts in Apple Mail.

  1. Then, outside the app, open the Apple menu and click System Preferences
  2. In the new window, double-click Profiles.
  3. In the new window, select your ProtonMail account and remove it by clicking on the “” button in the lower left corner.

Screenshot of macOS Profiles.

Thunderbird

  1. Open Thunderbird.
  2. From the menu, select Tools, and then click Account Settings.
  3. In the new window, select your ProtonMail account, click on the Account Actions button and select Remove account.

Screenshot of Thunderbird.
Screenshot of Account Settings in Thunderbird.

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

Screenshot of Removing Account and Data in Thunderbird.

2. Clear cache inside Bridge

  1. Open Proton Bridge.
  2. Go to Settings.
  3. Select Clear Cache.

This will cause Bridge to restart.

Screenshot of clearing Proton Bridge's cache.

3. Retry the setup process

Follow one of our easy step-by-step guides to successfully complete your setup. 

Still encountering problems setting up your Mail client with Proton Bridge? Contact our support team or check out some of the relevant articles below.

Relevant Articles 

Invalid password while setting up Email client
Bridge port already occupied error
Adding multiple accounts to Bridge