I would like to recommend you to download Vartika Zimbra to Office 365 Converter to import Zimbra to Office 365 account without any data loss. The tool maintains Zimbra items such as emails, contacts, calendar, notes, tasks, and etc You can get an easy migration of all your emails, contacts, tasks, journals, notes, attachments, etc. from TGZ file to PST, EML, EMLX, MBOX, PDF, HTML, MHTML format. And you can export Zimbra files to cloud-based mail, like Yahoo, Gmail, G Suite, Office 365, and Hotmail Account. 

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