If you want to migrate Zimbra file to PST then you can try any commercial application like KDETools Zimbra to PST Converter. Some features are:

Export Zimbra file to PST and additional file format such as EML, EMLX, HTML, PDF and etc.

This tool also migrate Zimbra file to Gmail, G Suit, Google Drive and etc.

This application shows a preview of Zimbra emails, contacts, calendars, briefcase, and all before conversion.

This application maintain folder Structure during the conversion process.

This application in all versions of Windows such as 7, 8 and 8.1, XP, 10 and so on.

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