If you want to migrate Zimbra to Gmail then you can try third-party software like Zimbra to Gmail Migration Tool. The software easily migrate Zimbra to Gmail, G Suite, Google Drive and etc. The software also migrates Zimbra to different file formats such as PST, MBOX, EML, EMLX, HTML, PDF, NSF, OLM and etc. The application allows the user to migrate the oversized Zimbra files to Gmail without any data loss.
Read More: https://www.kdetools.com/zimbra/gmail/