Port already occupied error (Proton Mail Bridge)

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Common issues and questions

Ports are the virtual endpoints of a network connection. All kinds of networked programs use the ports on your device to connect with the internet, including Proton Mail Bridge(new window).

Bridge uses ports 1143 and 1025 by default. But sometimes one or both of these ports are already in use by another application, such as voice over IP, streaming media apps, another email service, etc. If that happens, you will see a “port already occupied” error.

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The error message may appear before you configure your email client or at any point afterward if another app begins using the Bridge ports.

The first step to resolving this issue is to change the port numbers used by Bridge.

Changing port numbers in Bridge

To assign Bridge new port numbers, go to Settings Advanced settings Change SMTP/IMAP Ports.

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From there, you can increase the port number by one (i.e. 1144 for IMAP / 1026 for SMTP).

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If you receive the error again, continue to increase the port numbers incrementally until you no longer receive the error.

Updating port numbers in client settings

If you have not yet configured your email client, follow the instructions for your client(new window). The client configuration will automatically identify the ports Bridge is using. There’s nothing more you need to do.

However, if you have already completed client configuration, then you will need to update the ports in your client settings. This process is slightly different for each client.

Thunderbird

1. Right-click on the account address on the left side.

2. Select Settings Server settings. There you can change ports.

Outlook

1. Click on File Account settings.

2. Select your email address and click Change, and go to More Settings → Advanced. There you can change ports.

Apple Mail

1. Since this step is configured automatically in Apple Mail, you’ll need to first change the ports in the Bridge app via Settings Advanced settings Change SMTP/IMAP Ports.

2. Then set up your account with Apple Mail by clicking on Bridge. Under your account username, click on Configure Apple Mail and the port numbers will be updated automatically.

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