I would like to suggest you safe application Zimbra to Office 365 Converter Tool to import Zimbra to Office 365 file format.
Features:
• Support numerous file formats such as PST, MBOX, PDF, EML, EMLX, HTML, etc.
• This application directly import Zimbra file to Office 365 and Exchange Server account.
• This application allows all MS Outlook version such as 2019, 2016, 2013, 2010, 2007, 2003 and etc.
Read more: https://www.kdetools.com/zimbra/office-365.html