You can use Advance software like KDETools Zimbra to Office 365 Converter tool.
Some main features are:
• This tool is quickly import Zimbra file to Office 365 without facing any hassle.
• This application also simply import Zimbra file to Gmail, Exchange Server and etc without any hassle.
• This software also import Zimbra files to Office 365 and other file formats such as PST, MBOX, NSF, EML, EMLX, PDF, HTML, etc.
This tool shows free preview of the data before the conversion process.
Read More: https://www.kdetools.com/zimbra/office-365/