You can convert Zimbra to Office 365, you can try manual solutions and third-party solutions. KDETools Zimbra to Office 365 Converter is the most recommended software that easily convert Zimbra files to PST, MSG, EML, HTML and PDF file format. The tool carefully export emails, email properties, and attachments to Outlook PST.
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https://www.kdetools.com/zimbra/office-365.html