How to migrate Zimbra to Office 365
I would like to suggest commercial solution like Zimbra to Office 365 Converter Software. This tool gives you a faster process to export Zimbra file to Office 365 and Exchange Server. This software export Zimbra items such as emails, appointments, contacts, tasks list, journals, notes, and etc. This application export Zimbra file to Office 365 and multiple file-formats including EML, MSG, EMLX, vCard, vCal, an etc.
Read more: https://www.kdetools.com/blog/migrate-zimbra-to-office-365-directly.html

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John Merritt commented
To migrate Zimbra to Office 365 safely and securely, you can take the help of a professional utility like Softaken TGZ to Office 365 Importer Software. This utility smoothly migrates any size of Zimbra TGZ files into any Office 365 Account directly. This expert utility supports all versions of Zimbra Desktop TGZ files. Also, this application is useful for all users whether they are technically inclined or not. Furthermore, this importer tool works effortlessly in all the editions of Windows OS.
Read More: https://www.softaken.com/tgz-to-office-365-importer