I would like to suggest gainful software like KDETools Zimbra to Gmail Converter.
Features such as:
• This tool easily convert Zimbra to Gmail, G Suite, Google Drive and etc.
• This tool also simply convert Zimbra file to Office 365and Exchange Server without any hassle.
• This tool has batch conversion option.
• This tool easily convert multiple file formats such as PST, MBOX, OLM, EML, EMLX, HTML, and etc.
Read More: https://www.kdetools.com/zimbra/gmail/