You can try profitable solution like KDETools Zimbra to Gmail Converter Tool is the greatest tool for import Zimbra to Gmail. Some additional features are:

• Directly import Zimbra to Gmail, G Suite, Google Drive and etc.
• This application import Zimbra to other file formats like PST, OLM, NSF, MBOX, PDF, EML, EMLX, HTML, etc.
• This application does not make any changes while migrating.
• This application directly import Zimbra file to Office 365 and Exchange Server account.
• This application has Fast conversion of data without losing any data.
• This application shows a free preview of the data before the conversion process.
• This application works on all versions of Windows, including 7, 8, 8.1, XP, and 10.

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