In the How to Download Google Data from Spinbackup to a Local Device article, you learned the steps to download one item, several items, and the entire Google application. If you download several Gmail messages or the entire application, the downloaded items will be in MBOX format. So, you need to use the Import-Export Tools Add-On on Thunderbird.
1. First, download the free Thunderbird email application.
2. Download the Import-Export Tools Add-On from https://addons.mozilla.org/en-US/thunderbird/addon/importexporttools/.
3. Open Thunderbird, press the Tools menu, and click Add-ons. The Add-ons Manager tab will open.
4. Press the settings button next to the add-on search field and select Install Add-on From File. Choose the downloaded file.
5. You will need to restart Thunderbird. Next, the add-on will be installed. Press the Tools menu and click Import-Export Tools. Then select Import mbox file. Choose import and press Ok. Select the required folders from the unpacked archive downloaded from Spinbackup.
Please note: The mbox file can be imported only in the Local folders subfolder.
Now, you can view and use all downloaded messages.