While roundcube doesn't offer the function to export all email, it will usually allow you to connect a desktop mail client via IMAP with that functionality.

I recommend using an open source mail client such as [[https://www.thunderbird.net/en-US/|Thunderbird]], as it's free and well supported.

  - Download and install Thunderbird
  - Use IMAP to connect to your email 
    - Example settings: {{ ::imap-example-settings.png?400 |}}
  - Wait for emails to download
  - In the top menu bar, go to Tools > Export to export all emails