Try KDETools Zimbra to Gmail Migration Tool is the most capable tool to migrate Zimbra to Gmail account. Some features are:
• Zimbra to Gmail converter tool basically migrate Zimbra files to Gmail account, and other file formats such as G Suite, Google Drive and etc.
• Support numerous file formats such as PST, OLM, NSF, MBOX, PDF, EML, EMLX, HTML, etc.
• Migrate Zimbra file into Office 365 mailbox and Online Exchange this two format use for online Conversion.
• This tool also shows preview item before completing scanning process.
• You can mainly set off this tool in all versions of Windows such as 7, 8 and 8.1, XP, 10 and so on.
Read More: https://www.kdetools.com/zimbra/gmail/