We highly recommend you download the MailsDaddy Zimbra Converter tool to export data from TGZ to PT format. It manages all folder structures, headers, inline images, contacts, calendars, tasks, etc. in a new PST file. The free demo version of the software converts up to 20 emails from each folder.
Read more: https://www.mailsdaddy.com/blogs/native-method-to-backup-zimbra-mailbox-in-local-drive/