I would like to suggest a commercial solution like TGZ to Outlook Converter Software. This tool import TGZ items like emails, contacts, journals, notes, etc. This app import TGZ to Outlook and various file formats including PST, EML, MSG, EMLX, vCard, vCal, etc.
Read more:
http://www.olm-converter.com/tgz-extension/how-to-import-zimbra-tgz-to-pst-manually.html
