You can try commercial solution like KDETools Zimbra to Outlook Converter Tool is the most powerful tool for migrating Zimbra to Outlook PST. Some additional features are:

Zimbra converter convert Zimbra TGZ file to PST other file formats like OLM, NSF, MBOX, PDF, EML, EMLX, HTML, etc.

This tool has Fast conversion of data without losing any data.

Corrupted file also transformed securely.

This tool works on all versions of Windows, including 7, 8, 8.1, XP, and 10.

Read More: https://www.kdetools.com/zimbra/