Mozilla Thunderbird stores the text content of emails and other various settings in mbox files. These files are stored for each of your Thunderbird profiles in a collective folder called "Profiles." Mbox files can be imported and exported by simply downloading a Thunderbird add-on.
Go to the ImportExport Tools website (see "References"). Right click on the download link and select "Save Target/Link As."
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Save the XPI file to your computer's hard disk. Remember the save location.
Launch Thunderbird. Select "Add-ons" from the "Tools" menu.
Select "Extensions" in the new window. Click "Install."
Navigate to your saved ImportExport Tools XPI file and click "Open."
Click "Install Now" and close Thunderbird.
Restart Thunderbird. Select "Import/Export in mbox/eml format" from the "Tools" menu. Click "Import mbox file."
Navigate to the mbox file you want to import and click "Open."