Go to http://www.zmigrator.com/mozilla-thunderbird/ to download Zimbra to Thunderbird migration tool to convert TGZ files

to MBOX format.

Run Zimbra to Thunderbird Converter Software.

Click on Add Files or Add Folders to browse TGZ file / folder and press Open to load data in software panel.

Select required folders to migrate in Thunderbird format and click on any email to read information with attachments.

Click on Convert button to continue the process, select MBOX format and press Convert button to start the process.

This software also gives separate option to convert Zimbra contacts to Thunderbird as showing in screenshot.

Showing a message Conversion completed successfully

Now run Mozilla Thunderbird and select ImportExport option to import resultant MBOX files in Thunderbird

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